1 <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
2 "http://www.w3.org/TR/html4/strict.dtd">
5 <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
6 <title>Source Level Debugging with LLVM</title>
7 <link rel="stylesheet" href="llvm.css" type="text/css">
11 <div class="doc_title">Source Level Debugging with LLVM</div>
13 <table class="layout" style="width:100%">
17 <li><a href="#introduction">Introduction</a>
19 <li><a href="#phil">Philosophy behind LLVM debugging information</a></li>
20 <li><a href="#consumers">Debug information consumers</a></li>
21 <li><a href="#debugopt">Debugging optimized code</a></li>
23 <li><a href="#format">Debugging information format</a>
25 <li><a href="#debug_info_descriptors">Debug information descriptors</a>
27 <li><a href="#format_compile_units">Compile unit descriptors</a></li>
28 <li><a href="#format_files">File descriptors</a></li>
29 <li><a href="#format_global_variables">Global variable descriptors</a></li>
30 <li><a href="#format_subprograms">Subprogram descriptors</a></li>
31 <li><a href="#format_blocks">Block descriptors</a></li>
32 <li><a href="#format_basic_type">Basic type descriptors</a></li>
33 <li><a href="#format_derived_type">Derived type descriptors</a></li>
34 <li><a href="#format_composite_type">Composite type descriptors</a></li>
35 <li><a href="#format_subrange">Subrange descriptors</a></li>
36 <li><a href="#format_enumeration">Enumerator descriptors</a></li>
37 <li><a href="#format_variables">Local variables</a></li>
39 <li><a href="#format_common_intrinsics">Debugger intrinsic functions</a>
41 <li><a href="#format_common_declare">llvm.dbg.declare</a></li>
42 <li><a href="#format_common_value">llvm.dbg.value</a></li>
45 <li><a href="#format_common_lifetime">Object lifetimes and scoping</a></li>
46 <li><a href="#ccxx_frontend">C/C++ front-end specific debug information</a>
48 <li><a href="#ccxx_compile_units">C/C++ source file information</a></li>
49 <li><a href="#ccxx_global_variable">C/C++ global variable information</a></li>
50 <li><a href="#ccxx_subprogram">C/C++ function information</a></li>
51 <li><a href="#ccxx_basic_types">C/C++ basic types</a></li>
52 <li><a href="#ccxx_derived_types">C/C++ derived types</a></li>
53 <li><a href="#ccxx_composite_types">C/C++ struct/union types</a></li>
54 <li><a href="#ccxx_enumeration_types">C/C++ enumeration types</a></li>
59 <img src="img/venusflytrap.jpg" alt="A leafy and green bug eater" width="247"
64 <div class="doc_author">
65 <p>Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a>
66 and <a href="mailto:jlaskey@mac.com">Jim Laskey</a></p>
70 <!-- *********************************************************************** -->
71 <div class="doc_section"><a name="introduction">Introduction</a></div>
72 <!-- *********************************************************************** -->
74 <div class="doc_text">
76 <p>This document is the central repository for all information pertaining to
77 debug information in LLVM. It describes the <a href="#format">actual format
78 that the LLVM debug information</a> takes, which is useful for those
79 interested in creating front-ends or dealing directly with the information.
80 Further, this document provides specific examples of what debug information
85 <!-- ======================================================================= -->
86 <div class="doc_subsection">
87 <a name="phil">Philosophy behind LLVM debugging information</a>
90 <div class="doc_text">
92 <p>The idea of the LLVM debugging information is to capture how the important
93 pieces of the source-language's Abstract Syntax Tree map onto LLVM code.
94 Several design aspects have shaped the solution that appears here. The
95 important ones are:</p>
98 <li>Debugging information should have very little impact on the rest of the
99 compiler. No transformations, analyses, or code generators should need to
100 be modified because of debugging information.</li>
102 <li>LLVM optimizations should interact in <a href="#debugopt">well-defined and
103 easily described ways</a> with the debugging information.</li>
105 <li>Because LLVM is designed to support arbitrary programming languages,
106 LLVM-to-LLVM tools should not need to know anything about the semantics of
107 the source-level-language.</li>
109 <li>Source-level languages are often <b>widely</b> different from one another.
110 LLVM should not put any restrictions of the flavor of the source-language,
111 and the debugging information should work with any language.</li>
113 <li>With code generator support, it should be possible to use an LLVM compiler
114 to compile a program to native machine code and standard debugging
115 formats. This allows compatibility with traditional machine-code level
116 debuggers, like GDB or DBX.</li>
119 <p>The approach used by the LLVM implementation is to use a small set
120 of <a href="#format_common_intrinsics">intrinsic functions</a> to define a
121 mapping between LLVM program objects and the source-level objects. The
122 description of the source-level program is maintained in LLVM metadata
123 in an <a href="#ccxx_frontend">implementation-defined format</a>
124 (the C/C++ front-end currently uses working draft 7 of
125 the <a href="http://www.eagercon.com/dwarf/dwarf3std.htm">DWARF 3
128 <p>When a program is being debugged, a debugger interacts with the user and
129 turns the stored debug information into source-language specific information.
130 As such, a debugger must be aware of the source-language, and is thus tied to
131 a specific language or family of languages.</p>
135 <!-- ======================================================================= -->
136 <div class="doc_subsection">
137 <a name="consumers">Debug information consumers</a>
140 <div class="doc_text">
142 <p>The role of debug information is to provide meta information normally
143 stripped away during the compilation process. This meta information provides
144 an LLVM user a relationship between generated code and the original program
147 <p>Currently, debug information is consumed by the DwarfWriter to produce dwarf
148 information used by the gdb debugger. Other targets could use the same
149 information to produce stabs or other debug forms.</p>
151 <p>It would also be reasonable to use debug information to feed profiling tools
152 for analysis of generated code, or, tools for reconstructing the original
153 source from generated code.</p>
155 <p>TODO - expound a bit more.</p>
159 <!-- ======================================================================= -->
160 <div class="doc_subsection">
161 <a name="debugopt">Debugging optimized code</a>
164 <div class="doc_text">
166 <p>An extremely high priority of LLVM debugging information is to make it
167 interact well with optimizations and analysis. In particular, the LLVM debug
168 information provides the following guarantees:</p>
171 <li>LLVM debug information <b>always provides information to accurately read
172 the source-level state of the program</b>, regardless of which LLVM
173 optimizations have been run, and without any modification to the
174 optimizations themselves. However, some optimizations may impact the
175 ability to modify the current state of the program with a debugger, such
176 as setting program variables, or calling functions that have been
179 <li>LLVM optimizations gracefully interact with debugging information. If
180 they are not aware of debug information, they are automatically disabled
181 as necessary in the cases that would invalidate the debug info. This
182 retains the LLVM features, making it easy to write new
183 transformations.</li>
185 <li>As desired, LLVM optimizations can be upgraded to be aware of the LLVM
186 debugging information, allowing them to update the debugging information
187 as they perform aggressive optimizations. This means that, with effort,
188 the LLVM optimizers could optimize debug code just as well as non-debug
191 <li>LLVM debug information does not prevent many important optimizations from
192 happening (for example inlining, basic block reordering/merging/cleanup,
193 tail duplication, etc), further reducing the amount of the compiler that
194 eventually is "aware" of debugging information.</li>
196 <li>LLVM debug information is automatically optimized along with the rest of
197 the program, using existing facilities. For example, duplicate
198 information is automatically merged by the linker, and unused information
199 is automatically removed.</li>
202 <p>Basically, the debug information allows you to compile a program with
203 "<tt>-O0 -g</tt>" and get full debug information, allowing you to arbitrarily
204 modify the program as it executes from a debugger. Compiling a program with
205 "<tt>-O3 -g</tt>" gives you full debug information that is always available
206 and accurate for reading (e.g., you get accurate stack traces despite tail
207 call elimination and inlining), but you might lose the ability to modify the
208 program and call functions where were optimized out of the program, or
209 inlined away completely.</p>
211 <p><a href="TestingGuide.html#quicktestsuite">LLVM test suite</a> provides a
212 framework to test optimizer's handling of debugging information. It can be
215 <div class="doc_code">
217 % cd llvm/projects/test-suite/MultiSource/Benchmarks # or some other level
222 <p>This will test impact of debugging information on optimization passes. If
223 debugging information influences optimization passes then it will be reported
224 as a failure. See <a href="TestingGuide.html">TestingGuide</a> for more
225 information on LLVM test infrastructure and how to run various tests.</p>
229 <!-- *********************************************************************** -->
230 <div class="doc_section">
231 <a name="format">Debugging information format</a>
233 <!-- *********************************************************************** -->
235 <div class="doc_text">
237 <p>LLVM debugging information has been carefully designed to make it possible
238 for the optimizer to optimize the program and debugging information without
239 necessarily having to know anything about debugging information. In
240 particular, the use of metadata avoids duplicated debugging information from
241 the beginning, and the global dead code elimination pass automatically
242 deletes debugging information for a function if it decides to delete the
245 <p>To do this, most of the debugging information (descriptors for types,
246 variables, functions, source files, etc) is inserted by the language
247 front-end in the form of LLVM metadata. </p>
249 <p>Debug information is designed to be agnostic about the target debugger and
250 debugging information representation (e.g. DWARF/Stabs/etc). It uses a
251 generic pass to decode the information that represents variables, types,
252 functions, namespaces, etc: this allows for arbitrary source-language
253 semantics and type-systems to be used, as long as there is a module
254 written for the target debugger to interpret the information. </p>
256 <p>To provide basic functionality, the LLVM debugger does have to make some
257 assumptions about the source-level language being debugged, though it keeps
258 these to a minimum. The only common features that the LLVM debugger assumes
259 exist are <a href="#format_files">source files</a>,
260 and <a href="#format_global_variables">program objects</a>. These abstract
261 objects are used by a debugger to form stack traces, show information about
262 local variables, etc.</p>
264 <p>This section of the documentation first describes the representation aspects
265 common to any source-language. The <a href="#ccxx_frontend">next section</a>
266 describes the data layout conventions used by the C and C++ front-ends.</p>
270 <!-- ======================================================================= -->
271 <div class="doc_subsection">
272 <a name="debug_info_descriptors">Debug information descriptors</a>
275 <div class="doc_text">
277 <p>In consideration of the complexity and volume of debug information, LLVM
278 provides a specification for well formed debug descriptors. </p>
280 <p>Consumers of LLVM debug information expect the descriptors for program
281 objects to start in a canonical format, but the descriptors can include
282 additional information appended at the end that is source-language
283 specific. All LLVM debugging information is versioned, allowing backwards
284 compatibility in the case that the core structures need to change in some
285 way. Also, all debugging information objects start with a tag to indicate
286 what type of object it is. The source-language is allowed to define its own
287 objects, by using unreserved tag numbers. We recommend using with tags in
288 the range 0x1000 through 0x2000 (there is a defined enum DW_TAG_user_base =
291 <p>The fields of debug descriptors used internally by LLVM
292 are restricted to only the simple data types <tt>int</tt>, <tt>uint</tt>,
293 <tt>bool</tt>, <tt>float</tt>, <tt>double</tt>, <tt>mdstring</tt> and
294 <tt>mdnode</tt>. </p>
296 <div class="doc_code">
305 <p><a name="LLVMDebugVersion">The first field of a descriptor is always an
306 <tt>uint</tt> containing a tag value identifying the content of the
307 descriptor. The remaining fields are specific to the descriptor. The values
308 of tags are loosely bound to the tag values of DWARF information entries.
309 However, that does not restrict the use of the information supplied to DWARF
310 targets. To facilitate versioning of debug information, the tag is augmented
311 with the current debug version (LLVMDebugVersion = 8 << 16 or 0x80000 or
314 <p>The details of the various descriptors follow.</p>
318 <!-- ======================================================================= -->
319 <div class="doc_subsubsection">
320 <a name="format_compile_units">Compile unit descriptors</a>
323 <div class="doc_text">
325 <div class="doc_code">
328 i32, ;; Tag = 17 + <a href="#LLVMDebugVersion">LLVMDebugVersion</a>
329 ;; (DW_TAG_compile_unit)
330 i32, ;; Unused field.
331 i32, ;; DWARF language identifier (ex. DW_LANG_C89)
332 metadata, ;; Source file name
333 metadata, ;; Source file directory (includes trailing slash)
334 metadata ;; Producer (ex. "4.0.1 LLVM (LLVM research group)")
335 i1, ;; True if this is a main compile unit.
336 i1, ;; True if this is optimized.
338 i32 ;; Runtime version
343 <p>These descriptors contain a source language ID for the file (we use the DWARF
344 3.0 ID numbers, such as <tt>DW_LANG_C89</tt>, <tt>DW_LANG_C_plus_plus</tt>,
345 <tt>DW_LANG_Cobol74</tt>, etc), three strings describing the filename,
346 working directory of the compiler, and an identifier string for the compiler
347 that produced it.</p>
349 <p>Compile unit descriptors provide the root context for objects declared in a
350 specific compilation unit. File descriptors are defined using this context.</p>
354 <!-- ======================================================================= -->
355 <div class="doc_subsubsection">
356 <a name="format_files">File descriptors</a>
359 <div class="doc_text">
361 <div class="doc_code">
364 i32, ;; Tag = 41 + <a href="#LLVMDebugVersion">LLVMDebugVersion</a>
365 ;; (DW_TAG_file_type)
366 metadata, ;; Source file name
367 metadata, ;; Source file directory (includes trailing slash)
368 metadata ;; Reference to compile unit where defined
373 <p>These descriptors contain information for a file. Global variables and top
374 level functions would be defined using this context.k File descriptors also
375 provide context for source line correspondence. </p>
377 <p>Each input file is encoded as a separate file descriptor in LLVM debugging
378 information output. Each file descriptor would be defined using a
383 <!-- ======================================================================= -->
384 <div class="doc_subsubsection">
385 <a name="format_global_variables">Global variable descriptors</a>
388 <div class="doc_text">
390 <div class="doc_code">
393 i32, ;; Tag = 52 + <a href="#LLVMDebugVersion">LLVMDebugVersion</a>
395 i32, ;; Unused field.
396 metadata, ;; Reference to context descriptor
398 metadata, ;; Display name (fully qualified C++ name)
399 metadata, ;; MIPS linkage name (for C++)
400 metadata, ;; Reference to file where defined
401 i32, ;; Line number where defined
402 metadata, ;; Reference to type descriptor
403 i1, ;; True if the global is local to compile unit (static)
404 i1, ;; True if the global is defined in the compile unit (not extern)
405 { }* ;; Reference to the global variable
410 <p>These descriptors provide debug information about globals variables. The
411 provide details such as name, type and where the variable is defined.</p>
415 <!-- ======================================================================= -->
416 <div class="doc_subsubsection">
417 <a name="format_subprograms">Subprogram descriptors</a>
420 <div class="doc_text">
422 <div class="doc_code">
425 i32, ;; Tag = 46 + <a href="#LLVMDebugVersion">LLVMDebugVersion</a>
426 ;; (DW_TAG_subprogram)
427 i32, ;; Unused field.
428 metadata, ;; Reference to context descriptor
430 metadata, ;; Display name (fully qualified C++ name)
431 metadata, ;; MIPS linkage name (for C++)
432 metadata, ;; Reference to file where defined
433 i32, ;; Line number where defined
434 metadata, ;; Reference to type descriptor
435 i1, ;; True if the global is local to compile unit (static)
436 i1 ;; True if the global is defined in the compile unit (not extern)
441 <p>These descriptors provide debug information about functions, methods and
442 subprograms. They provide details such as name, return types and the source
443 location where the subprogram is defined.</p>
447 <!-- ======================================================================= -->
448 <div class="doc_subsubsection">
449 <a name="format_blocks">Block descriptors</a>
452 <div class="doc_text">
454 <div class="doc_code">
457 i32, ;; Tag = 13 + <a href="#LLVMDebugVersion">LLVMDebugVersion</a> (DW_TAG_lexical_block)
458 metadata ;; Reference to context descriptor
463 <p>These descriptors provide debug information about nested blocks within a
464 subprogram. The array of member descriptors is used to define local
465 variables and deeper nested blocks.</p>
469 <!-- ======================================================================= -->
470 <div class="doc_subsubsection">
471 <a name="format_basic_type">Basic type descriptors</a>
474 <div class="doc_text">
476 <div class="doc_code">
479 i32, ;; Tag = 36 + <a href="#LLVMDebugVersion">LLVMDebugVersion</a>
480 ;; (DW_TAG_base_type)
481 metadata, ;; Reference to context (typically a compile unit)
482 metadata, ;; Name (may be "" for anonymous types)
483 metadata, ;; Reference to file where defined (may be NULL)
484 i32, ;; Line number where defined (may be 0)
486 i64, ;; Alignment in bits
487 i64, ;; Offset in bits
489 i32 ;; DWARF type encoding
494 <p>These descriptors define primitive types used in the code. Example int, bool
495 and float. The context provides the scope of the type, which is usually the
496 top level. Since basic types are not usually user defined the compile unit
497 and line number can be left as NULL and 0. The size, alignment and offset
498 are expressed in bits and can be 64 bit values. The alignment is used to
499 round the offset when embedded in a
500 <a href="#format_composite_type">composite type</a> (example to keep float
501 doubles on 64 bit boundaries.) The offset is the bit offset if embedded in
502 a <a href="#format_composite_type">composite type</a>.</p>
504 <p>The type encoding provides the details of the type. The values are typically
505 one of the following:</p>
507 <div class="doc_code">
513 DW_ATE_signed_char = 6
515 DW_ATE_unsigned_char = 8
521 <!-- ======================================================================= -->
522 <div class="doc_subsubsection">
523 <a name="format_derived_type">Derived type descriptors</a>
526 <div class="doc_text">
528 <div class="doc_code">
531 i32, ;; Tag (see below)
532 metadata, ;; Reference to context
533 metadata, ;; Name (may be "" for anonymous types)
534 metadata, ;; Reference to file where defined (may be NULL)
535 i32, ;; Line number where defined (may be 0)
537 i32, ;; Alignment in bits
538 i32, ;; Offset in bits
539 metadata ;; Reference to type derived from
544 <p>These descriptors are used to define types derived from other types. The
545 value of the tag varies depending on the meaning. The following are possible
548 <div class="doc_code">
550 DW_TAG_formal_parameter = 5
552 DW_TAG_pointer_type = 15
553 DW_TAG_reference_type = 16
555 DW_TAG_const_type = 38
556 DW_TAG_volatile_type = 53
557 DW_TAG_restrict_type = 55
561 <p><tt>DW_TAG_member</tt> is used to define a member of
562 a <a href="#format_composite_type">composite type</a>
563 or <a href="#format_subprograms">subprogram</a>. The type of the member is
564 the <a href="#format_derived_type">derived
565 type</a>. <tt>DW_TAG_formal_parameter</tt> is used to define a member which
566 is a formal argument of a subprogram.</p>
568 <p><tt>DW_TAG_typedef</tt> is used to provide a name for the derived type.</p>
570 <p><tt>DW_TAG_pointer_type</tt>,<tt>DW_TAG_reference_type</tt>,
571 <tt>DW_TAG_const_type</tt>, <tt>DW_TAG_volatile_type</tt>
572 and <tt>DW_TAG_restrict_type</tt> are used to qualify
573 the <a href="#format_derived_type">derived type</a>. </p>
575 <p><a href="#format_derived_type">Derived type</a> location can be determined
576 from the compile unit and line number. The size, alignment and offset are
577 expressed in bits and can be 64 bit values. The alignment is used to round
578 the offset when embedded in a <a href="#format_composite_type">composite
579 type</a> (example to keep float doubles on 64 bit boundaries.) The offset is
580 the bit offset if embedded in a <a href="#format_composite_type">composite
583 <p>Note that the <tt>void *</tt> type is expressed as a
584 <tt>llvm.dbg.derivedtype.type</tt> with tag of <tt>DW_TAG_pointer_type</tt>
585 and <tt>NULL</tt> derived type.</p>
589 <!-- ======================================================================= -->
590 <div class="doc_subsubsection">
591 <a name="format_composite_type">Composite type descriptors</a>
594 <div class="doc_text">
596 <div class="doc_code">
599 i32, ;; Tag (see below)
600 metadata, ;; Reference to context
601 metadata, ;; Name (may be "" for anonymous types)
602 metadata, ;; Reference to file where defined (may be NULL)
603 i32, ;; Line number where defined (may be 0)
605 i64, ;; Alignment in bits
606 i64, ;; Offset in bits
608 metadata, ;; Reference to type derived from
609 metadata, ;; Reference to array of member descriptors
610 i32 ;; Runtime languages
615 <p>These descriptors are used to define types that are composed of 0 or more
616 elements. The value of the tag varies depending on the meaning. The following
617 are possible tag values:</p>
619 <div class="doc_code">
621 DW_TAG_array_type = 1
622 DW_TAG_enumeration_type = 4
623 DW_TAG_structure_type = 19
624 DW_TAG_union_type = 23
625 DW_TAG_vector_type = 259
626 DW_TAG_subroutine_type = 21
627 DW_TAG_inheritance = 28
631 <p>The vector flag indicates that an array type is a native packed vector.</p>
633 <p>The members of array types (tag = <tt>DW_TAG_array_type</tt>) or vector types
634 (tag = <tt>DW_TAG_vector_type</tt>) are <a href="#format_subrange">subrange
635 descriptors</a>, each representing the range of subscripts at that level of
638 <p>The members of enumeration types (tag = <tt>DW_TAG_enumeration_type</tt>) are
639 <a href="#format_enumeration">enumerator descriptors</a>, each representing
640 the definition of enumeration value for the set.</p>
642 <p>The members of structure (tag = <tt>DW_TAG_structure_type</tt>) or union (tag
643 = <tt>DW_TAG_union_type</tt>) types are any one of
644 the <a href="#format_basic_type">basic</a>,
645 <a href="#format_derived_type">derived</a>
646 or <a href="#format_composite_type">composite</a> type descriptors, each
647 representing a field member of the structure or union.</p>
649 <p>For C++ classes (tag = <tt>DW_TAG_structure_type</tt>), member descriptors
650 provide information about base classes, static members and member
651 functions. If a member is a <a href="#format_derived_type">derived type
652 descriptor</a> and has a tag of <tt>DW_TAG_inheritance</tt>, then the type
653 represents a base class. If the member of is
654 a <a href="#format_global_variables">global variable descriptor</a> then it
655 represents a static member. And, if the member is
656 a <a href="#format_subprograms">subprogram descriptor</a> then it represents
657 a member function. For static members and member
658 functions, <tt>getName()</tt> returns the members link or the C++ mangled
659 name. <tt>getDisplayName()</tt> the simplied version of the name.</p>
661 <p>The first member of subroutine (tag = <tt>DW_TAG_subroutine_type</tt>) type
662 elements is the return type for the subroutine. The remaining elements are
663 the formal arguments to the subroutine.</p>
665 <p><a href="#format_composite_type">Composite type</a> location can be
666 determined from the compile unit and line number. The size, alignment and
667 offset are expressed in bits and can be 64 bit values. The alignment is used
668 to round the offset when embedded in
669 a <a href="#format_composite_type">composite type</a> (as an example, to keep
670 float doubles on 64 bit boundaries.) The offset is the bit offset if embedded
671 in a <a href="#format_composite_type">composite type</a>.</p>
675 <!-- ======================================================================= -->
676 <div class="doc_subsubsection">
677 <a name="format_subrange">Subrange descriptors</a>
680 <div class="doc_text">
682 <div class="doc_code">
684 %<a href="#format_subrange">llvm.dbg.subrange.type</a> = type {
685 i32, ;; Tag = 33 + <a href="#LLVMDebugVersion">LLVMDebugVersion</a> (DW_TAG_subrange_type)
692 <p>These descriptors are used to define ranges of array subscripts for an array
693 <a href="#format_composite_type">composite type</a>. The low value defines
694 the lower bounds typically zero for C/C++. The high value is the upper
695 bounds. Values are 64 bit. High - low + 1 is the size of the array. If low
696 == high the array will be unbounded.</p>
700 <!-- ======================================================================= -->
701 <div class="doc_subsubsection">
702 <a name="format_enumeration">Enumerator descriptors</a>
705 <div class="doc_text">
707 <div class="doc_code">
710 i32, ;; Tag = 40 + <a href="#LLVMDebugVersion">LLVMDebugVersion</a>
711 ;; (DW_TAG_enumerator)
718 <p>These descriptors are used to define members of an
719 enumeration <a href="#format_composite_type">composite type</a>, it
720 associates the name to the value.</p>
724 <!-- ======================================================================= -->
725 <div class="doc_subsubsection">
726 <a name="format_variables">Local variables</a>
729 <div class="doc_text">
731 <div class="doc_code">
734 i32, ;; Tag (see below)
737 metadata, ;; Reference to file where defined
738 i32, ;; Line number where defined
739 metadata ;; Type descriptor
744 <p>These descriptors are used to define variables local to a sub program. The
745 value of the tag depends on the usage of the variable:</p>
747 <div class="doc_code">
749 DW_TAG_auto_variable = 256
750 DW_TAG_arg_variable = 257
751 DW_TAG_return_variable = 258
755 <p>An auto variable is any variable declared in the body of the function. An
756 argument variable is any variable that appears as a formal argument to the
757 function. A return variable is used to track the result of a function and
758 has no source correspondent.</p>
760 <p>The context is either the subprogram or block where the variable is defined.
761 Name the source variable name. Compile unit and line indicate where the
762 variable was defined. Type descriptor defines the declared type of the
767 <!-- ======================================================================= -->
768 <div class="doc_subsection">
769 <a name="format_common_intrinsics">Debugger intrinsic functions</a>
772 <div class="doc_text">
774 <p>LLVM uses several intrinsic functions (name prefixed with "llvm.dbg") to
775 provide debug information at various points in generated code.</p>
779 <!-- ======================================================================= -->
780 <div class="doc_subsubsection">
781 <a name="format_common_declare">llvm.dbg.declare</a>
784 <div class="doc_text">
786 void %<a href="#format_common_declare">llvm.dbg.declare</a>( { } *, metadata )
789 <p>This intrinsic provides information about a local element (ex. variable.) The
790 first argument is the alloca for the variable, cast to a <tt>{ }*</tt>. The
792 the <tt>%<a href="#format_variables">llvm.dbg.variable</a></tt> containing
793 the description of the variable. </p>
797 <!-- ======================================================================= -->
798 <div class="doc_subsubsection">
799 <a name="format_common_value">llvm.dbg.value</a>
802 <div class="doc_text">
804 void %<a href="#format_common_value">llvm.dbg.value</a>( metadata, i64, metadata )
807 <p>This intrinsic provides information when a user source variable is set to a
808 new value. The first argument is the new value (wrapped as metadata). The
809 second argument is the offset in the user source variable where the new value
810 is written. The third argument is
811 the <tt>%<a href="#format_variables">llvm.dbg.variable</a></tt> containing
812 the description of the user source variable. </p>
816 <!-- ======================================================================= -->
817 <div class="doc_subsection">
818 <a name="format_common_lifetime">Object lifetimes and scoping</a>
821 <div class="doc_text">
822 <p>In many languages, the local variables in functions can have their lifetimes
823 or scopes limited to a subset of a function. In the C family of languages,
824 for example, variables are only live (readable and writable) within the
825 source block that they are defined in. In functional languages, values are
826 only readable after they have been defined. Though this is a very obvious
827 concept, it is non-trivial to model in LLVM, because it has no notion of
828 scoping in this sense, and does not want to be tied to a language's scoping
831 <p>In order to handle this, the LLVM debug format uses the metadata attached to
832 llvm instructions to encode line nuber and scoping information. Consider the
833 following C fragment, for example:</p>
835 <div class="doc_code">
849 <p>Compiled to LLVM, this function would be represented like this:</p>
851 <div class="doc_code">
853 define void @foo() nounwind ssp {
855 %X = alloca i32, align 4 ; <i32*> [#uses=4]
856 %Y = alloca i32, align 4 ; <i32*> [#uses=4]
857 %Z = alloca i32, align 4 ; <i32*> [#uses=3]
858 %0 = bitcast i32* %X to { }* ; <{ }*> [#uses=1]
859 call void @llvm.dbg.declare({ }* %0, metadata !0), !dbg !7
860 store i32 21, i32* %X, !dbg !8
861 %1 = bitcast i32* %Y to { }* ; <{ }*> [#uses=1]
862 call void @llvm.dbg.declare({ }* %1, metadata !9), !dbg !10
863 store i32 22, i32* %Y, !dbg !11
864 %2 = bitcast i32* %Z to { }* ; <{ }*> [#uses=1]
865 call void @llvm.dbg.declare({ }* %2, metadata !12), !dbg !14
866 store i32 23, i32* %Z, !dbg !15
867 %tmp = load i32* %X, !dbg !16 ; <i32> [#uses=1]
868 %tmp1 = load i32* %Y, !dbg !16 ; <i32> [#uses=1]
869 %add = add nsw i32 %tmp, %tmp1, !dbg !16 ; <i32> [#uses=1]
870 store i32 %add, i32* %Z, !dbg !16
871 %tmp2 = load i32* %Y, !dbg !17 ; <i32> [#uses=1]
872 store i32 %tmp2, i32* %X, !dbg !17
876 declare void @llvm.dbg.declare({ }*, metadata) nounwind readnone
878 !0 = metadata !{i32 459008, metadata !1, metadata !"X",
879 metadata !3, i32 2, metadata !6}; [ DW_TAG_auto_variable ]
880 !1 = metadata !{i32 458763, metadata !2}; [DW_TAG_lexical_block ]
881 !2 = metadata !{i32 458798, i32 0, metadata !3, metadata !"foo", metadata !"foo",
882 metadata !"foo", metadata !3, i32 1, metadata !4,
883 i1 false, i1 true}; [DW_TAG_subprogram ]
884 !3 = metadata !{i32 458769, i32 0, i32 12, metadata !"foo.c",
885 metadata !"/private/tmp", metadata !"clang 1.1", i1 true,
886 i1 false, metadata !"", i32 0}; [DW_TAG_compile_unit ]
887 !4 = metadata !{i32 458773, metadata !3, metadata !"", null, i32 0, i64 0, i64 0,
888 i64 0, i32 0, null, metadata !5, i32 0}; [DW_TAG_subroutine_type ]
889 !5 = metadata !{null}
890 !6 = metadata !{i32 458788, metadata !3, metadata !"int", metadata !3, i32 0,
891 i64 32, i64 32, i64 0, i32 0, i32 5}; [DW_TAG_base_type ]
892 !7 = metadata !{i32 2, i32 7, metadata !1, null}
893 !8 = metadata !{i32 2, i32 3, metadata !1, null}
894 !9 = metadata !{i32 459008, metadata !1, metadata !"Y", metadata !3, i32 3,
895 metadata !6}; [ DW_TAG_auto_variable ]
896 !10 = metadata !{i32 3, i32 7, metadata !1, null}
897 !11 = metadata !{i32 3, i32 3, metadata !1, null}
898 !12 = metadata !{i32 459008, metadata !13, metadata !"Z", metadata !3, i32 5,
899 metadata !6}; [ DW_TAG_auto_variable ]
900 !13 = metadata !{i32 458763, metadata !1}; [DW_TAG_lexical_block ]
901 !14 = metadata !{i32 5, i32 9, metadata !13, null}
902 !15 = metadata !{i32 5, i32 5, metadata !13, null}
903 !16 = metadata !{i32 6, i32 5, metadata !13, null}
904 !17 = metadata !{i32 8, i32 3, metadata !1, null}
905 !18 = metadata !{i32 9, i32 1, metadata !2, null}
909 <p>This example illustrates a few important details about LLVM debugging
910 information. In particular, it shows how the <tt>llvm.dbg.declare</tt>
911 intrinsic and location information, which are attached to an instruction,
912 are applied together to allow a debugger to analyze the relationship between
913 statements, variable definitions, and the code used to implement the
916 <div class="doc_code">
918 call void @llvm.dbg.declare({ }* %0, metadata !0), !dbg !7
922 <p>The first intrinsic
923 <tt>%<a href="#format_common_declare">llvm.dbg.declare</a></tt>
924 encodes debugging information for the variable <tt>X</tt>. The metadata
925 <tt>!dbg !7</tt> attached to the intrinsic provides scope information for the
926 variable <tt>X</tt>.</p>
928 <div class="doc_code">
930 !7 = metadata !{i32 2, i32 7, metadata !1, null}
931 !1 = metadata !{i32 458763, metadata !2}; [DW_TAG_lexical_block ]
932 !2 = metadata !{i32 458798, i32 0, metadata !3, metadata !"foo",
933 metadata !"foo", metadata !"foo", metadata !3, i32 1,
934 metadata !4, i1 false, i1 true}; [DW_TAG_subprogram ]
938 <p>Here <tt>!7</tt> is metadata providing location information. It has four
939 fields: line number, column number, scope, and original scope. The original
940 scope represents inline location if this instruction is inlined inside a
941 caller, and is null otherwise. In this example, scope is encoded by
942 <tt>!1</tt>. <tt>!1</tt> represents a lexical block inside the scope
943 <tt>!2</tt>, where <tt>!2</tt> is a
944 <a href="#format_subprograms">subprogram descriptor</a>. This way the
945 location information attached to the intrinsics indicates that the
946 variable <tt>X</tt> is declared at line number 2 at a function level scope in
947 function <tt>foo</tt>.</p>
949 <p>Now lets take another example.</p>
951 <div class="doc_code">
953 call void @llvm.dbg.declare({ }* %2, metadata !12), !dbg !14
957 <p>The second intrinsic
958 <tt>%<a href="#format_common_declare">llvm.dbg.declare</a></tt>
959 encodes debugging information for variable <tt>Z</tt>. The metadata
960 <tt>!dbg !14</tt> attached to the intrinsic provides scope information for
961 the variable <tt>Z</tt>.</p>
963 <div class="doc_code">
965 !13 = metadata !{i32 458763, metadata !1}; [DW_TAG_lexical_block ]
966 !14 = metadata !{i32 5, i32 9, metadata !13, null}
970 <p>Here <tt>!14</tt> indicates that <tt>Z</tt> is declared at line number 5 and
971 column number 9 inside of lexical scope <tt>!13</tt>. The lexical scope
972 itself resides inside of lexical scope <tt>!1</tt> described above.</p>
974 <p>The scope information attached with each instruction provides a
975 straightforward way to find instructions covered by a scope.</p>
979 <!-- *********************************************************************** -->
980 <div class="doc_section">
981 <a name="ccxx_frontend">C/C++ front-end specific debug information</a>
983 <!-- *********************************************************************** -->
985 <div class="doc_text">
987 <p>The C and C++ front-ends represent information about the program in a format
988 that is effectively identical
989 to <a href="http://www.eagercon.com/dwarf/dwarf3std.htm">DWARF 3.0</a> in
990 terms of information content. This allows code generators to trivially
991 support native debuggers by generating standard dwarf information, and
992 contains enough information for non-dwarf targets to translate it as
995 <p>This section describes the forms used to represent C and C++ programs. Other
996 languages could pattern themselves after this (which itself is tuned to
997 representing programs in the same way that DWARF 3 does), or they could
998 choose to provide completely different forms if they don't fit into the DWARF
999 model. As support for debugging information gets added to the various LLVM
1000 source-language front-ends, the information used should be documented
1003 <p>The following sections provide examples of various C/C++ constructs and the
1004 debug information that would best describe those constructs.</p>
1008 <!-- ======================================================================= -->
1009 <div class="doc_subsection">
1010 <a name="ccxx_compile_units">C/C++ source file information</a>
1013 <div class="doc_text">
1015 <p>Given the source files <tt>MySource.cpp</tt> and <tt>MyHeader.h</tt> located
1016 in the directory <tt>/Users/mine/sources</tt>, the following code:</p>
1018 <div class="doc_code">
1020 #include "MyHeader.h"
1022 int main(int argc, char *argv[]) {
1028 <p>a C/C++ front-end would generate the following descriptors:</p>
1030 <div class="doc_code">
1034 ;; Define the compile unit for the main source file "/Users/mine/sources/MySource.cpp".
1039 i32 4, ;; Language Id
1040 metadata !"MySource.cpp",
1041 metadata !"/Users/mine/sources",
1042 metadata !"4.2.1 (Based on Apple Inc. build 5649) (LLVM build 00)",
1043 i1 true, ;; Main Compile Unit
1044 i1 false, ;; Optimized compile unit
1045 metadata !"", ;; Compiler flags
1046 i32 0} ;; Runtime version
1049 ;; Define the file for the file "/Users/mine/sources/MySource.cpp".
1053 metadata !"MySource.cpp",
1054 metadata !"/Users/mine/sources",
1055 metadata !3 ;; Compile unit
1059 ;; Define the file for the file "/Users/mine/sources/Myheader.h"
1063 metadata !"Myheader.h"
1064 metadata !"/Users/mine/sources",
1065 metadata !3 ;; Compile unit
1072 <p>llvm::Instruction provides easy access to metadata attached with an
1073 instruction. One can extract line number information encoded in LLVM IR
1074 using <tt>Instruction::getMetadata()</tt> and
1075 <tt>DILocation::getLineNumber()</tt>.
1077 if (MDNode *N = I->getMetadata("dbg")) { // Here I is an LLVM instruction
1078 DILocation Loc(N); // DILocation is in DebugInfo.h
1079 unsigned Line = Loc.getLineNumber();
1080 StringRef File = Loc.getFilename();
1081 StringRef Dir = Loc.getDirectory();
1086 <!-- ======================================================================= -->
1087 <div class="doc_subsection">
1088 <a name="ccxx_global_variable">C/C++ global variable information</a>
1091 <div class="doc_text">
1093 <p>Given an integer global variable declared as follows:</p>
1095 <div class="doc_code">
1101 <p>a C/C++ front-end would generate the following descriptors:</p>
1103 <div class="doc_code">
1106 ;; Define the global itself.
1108 %MyGlobal = global int 100
1111 ;; List of debug info of globals
1113 !llvm.dbg.gv = !{!0}
1116 ;; Define the global variable descriptor. Note the reference to the global
1117 ;; variable anchor and the global variable itself.
1122 metadata !1, ;; Context
1123 metadata !"MyGlobal", ;; Name
1124 metadata !"MyGlobal", ;; Display Name
1125 metadata !"MyGlobal", ;; Linkage Name
1126 metadata !3, ;; Compile Unit
1127 i32 1, ;; Line Number
1128 metadata !4, ;; Type
1129 i1 false, ;; Is a local variable
1130 i1 true, ;; Is this a definition
1131 i32* @MyGlobal ;; The global variable
1135 ;; Define the basic type of 32 bit signed integer. Note that since int is an
1136 ;; intrinsic type the source file is NULL and line 0.
1140 metadata !1, ;; Context
1141 metadata !"int", ;; Name
1142 metadata !1, ;; File
1143 i32 0, ;; Line number
1144 i64 32, ;; Size in Bits
1145 i64 32, ;; Align in Bits
1146 i64 0, ;; Offset in Bits
1156 <!-- ======================================================================= -->
1157 <div class="doc_subsection">
1158 <a name="ccxx_subprogram">C/C++ function information</a>
1161 <div class="doc_text">
1163 <p>Given a function declared as follows:</p>
1165 <div class="doc_code">
1167 int main(int argc, char *argv[]) {
1173 <p>a C/C++ front-end would generate the following descriptors:</p>
1175 <div class="doc_code">
1178 ;; Define the anchor for subprograms. Note that the second field of the
1179 ;; anchor is 46, which is the same as the tag for subprograms
1180 ;; (46 = DW_TAG_subprogram.)
1185 metadata !1, ;; Context
1186 metadata !"main", ;; Name
1187 metadata !"main", ;; Display name
1188 metadata !"main", ;; Linkage name
1189 metadata !1, ;; File
1190 i32 1, ;; Line number
1191 metadata !4, ;; Type
1192 i1 false, ;; Is local
1193 i1 true ;; Is definition
1196 ;; Define the subprogram itself.
1198 define i32 @main(i32 %argc, i8** %argv) {
1206 <!-- ======================================================================= -->
1207 <div class="doc_subsection">
1208 <a name="ccxx_basic_types">C/C++ basic types</a>
1211 <div class="doc_text">
1213 <p>The following are the basic type descriptors for C/C++ core types:</p>
1217 <!-- ======================================================================= -->
1218 <div class="doc_subsubsection">
1219 <a name="ccxx_basic_type_bool">bool</a>
1222 <div class="doc_text">
1224 <div class="doc_code">
1228 metadata !1, ;; Context
1229 metadata !"bool", ;; Name
1230 metadata !1, ;; File
1231 i32 0, ;; Line number
1232 i64 8, ;; Size in Bits
1233 i64 8, ;; Align in Bits
1234 i64 0, ;; Offset in Bits
1243 <!-- ======================================================================= -->
1244 <div class="doc_subsubsection">
1245 <a name="ccxx_basic_char">char</a>
1248 <div class="doc_text">
1250 <div class="doc_code">
1254 metadata !1, ;; Context
1255 metadata !"char", ;; Name
1256 metadata !1, ;; File
1257 i32 0, ;; Line number
1258 i64 8, ;; Size in Bits
1259 i64 8, ;; Align in Bits
1260 i64 0, ;; Offset in Bits
1269 <!-- ======================================================================= -->
1270 <div class="doc_subsubsection">
1271 <a name="ccxx_basic_unsigned_char">unsigned char</a>
1274 <div class="doc_text">
1276 <div class="doc_code">
1280 metadata !1, ;; Context
1281 metadata !"unsigned char",
1282 metadata !1, ;; File
1283 i32 0, ;; Line number
1284 i64 8, ;; Size in Bits
1285 i64 8, ;; Align in Bits
1286 i64 0, ;; Offset in Bits
1295 <!-- ======================================================================= -->
1296 <div class="doc_subsubsection">
1297 <a name="ccxx_basic_short">short</a>
1300 <div class="doc_text">
1302 <div class="doc_code">
1306 metadata !1, ;; Context
1307 metadata !"short int",
1308 metadata !1, ;; File
1309 i32 0, ;; Line number
1310 i64 16, ;; Size in Bits
1311 i64 16, ;; Align in Bits
1312 i64 0, ;; Offset in Bits
1321 <!-- ======================================================================= -->
1322 <div class="doc_subsubsection">
1323 <a name="ccxx_basic_unsigned_short">unsigned short</a>
1326 <div class="doc_text">
1328 <div class="doc_code">
1332 metadata !1, ;; Context
1333 metadata !"short unsigned int",
1334 metadata !1, ;; File
1335 i32 0, ;; Line number
1336 i64 16, ;; Size in Bits
1337 i64 16, ;; Align in Bits
1338 i64 0, ;; Offset in Bits
1347 <!-- ======================================================================= -->
1348 <div class="doc_subsubsection">
1349 <a name="ccxx_basic_int">int</a>
1352 <div class="doc_text">
1354 <div class="doc_code">
1358 metadata !1, ;; Context
1359 metadata !"int", ;; Name
1360 metadata !1, ;; File
1361 i32 0, ;; Line number
1362 i64 32, ;; Size in Bits
1363 i64 32, ;; Align in Bits
1364 i64 0, ;; Offset in Bits
1372 <!-- ======================================================================= -->
1373 <div class="doc_subsubsection">
1374 <a name="ccxx_basic_unsigned_int">unsigned int</a>
1377 <div class="doc_text">
1379 <div class="doc_code">
1383 metadata !1, ;; Context
1384 metadata !"unsigned int",
1385 metadata !1, ;; File
1386 i32 0, ;; Line number
1387 i64 32, ;; Size in Bits
1388 i64 32, ;; Align in Bits
1389 i64 0, ;; Offset in Bits
1398 <!-- ======================================================================= -->
1399 <div class="doc_subsubsection">
1400 <a name="ccxx_basic_long_long">long long</a>
1403 <div class="doc_text">
1405 <div class="doc_code">
1409 metadata !1, ;; Context
1410 metadata !"long long int",
1411 metadata !1, ;; File
1412 i32 0, ;; Line number
1413 i64 64, ;; Size in Bits
1414 i64 64, ;; Align in Bits
1415 i64 0, ;; Offset in Bits
1424 <!-- ======================================================================= -->
1425 <div class="doc_subsubsection">
1426 <a name="ccxx_basic_unsigned_long_long">unsigned long long</a>
1429 <div class="doc_text">
1431 <div class="doc_code">
1435 metadata !1, ;; Context
1436 metadata !"long long unsigned int",
1437 metadata !1, ;; File
1438 i32 0, ;; Line number
1439 i64 64, ;; Size in Bits
1440 i64 64, ;; Align in Bits
1441 i64 0, ;; Offset in Bits
1450 <!-- ======================================================================= -->
1451 <div class="doc_subsubsection">
1452 <a name="ccxx_basic_float">float</a>
1455 <div class="doc_text">
1457 <div class="doc_code">
1461 metadata !1, ;; Context
1463 metadata !1, ;; File
1464 i32 0, ;; Line number
1465 i64 32, ;; Size in Bits
1466 i64 32, ;; Align in Bits
1467 i64 0, ;; Offset in Bits
1476 <!-- ======================================================================= -->
1477 <div class="doc_subsubsection">
1478 <a name="ccxx_basic_double">double</a>
1481 <div class="doc_text">
1483 <div class="doc_code">
1487 metadata !1, ;; Context
1488 metadata !"double",;; Name
1489 metadata !1, ;; File
1490 i32 0, ;; Line number
1491 i64 64, ;; Size in Bits
1492 i64 64, ;; Align in Bits
1493 i64 0, ;; Offset in Bits
1502 <!-- ======================================================================= -->
1503 <div class="doc_subsection">
1504 <a name="ccxx_derived_types">C/C++ derived types</a>
1507 <div class="doc_text">
1509 <p>Given the following as an example of C/C++ derived type:</p>
1511 <div class="doc_code">
1513 typedef const int *IntPtr;
1517 <p>a C/C++ front-end would generate the following descriptors:</p>
1519 <div class="doc_code">
1522 ;; Define the typedef "IntPtr".
1526 metadata !1, ;; Context
1527 metadata !"IntPtr", ;; Name
1528 metadata !3, ;; File
1529 i32 0, ;; Line number
1530 i64 0, ;; Size in bits
1531 i64 0, ;; Align in bits
1532 i64 0, ;; Offset in bits
1534 metadata !4 ;; Derived From type
1538 ;; Define the pointer type.
1542 metadata !1, ;; Context
1543 metadata !"", ;; Name
1544 metadata !1, ;; File
1545 i32 0, ;; Line number
1546 i64 64, ;; Size in bits
1547 i64 64, ;; Align in bits
1548 i64 0, ;; Offset in bits
1550 metadata !5 ;; Derived From type
1553 ;; Define the const type.
1557 metadata !1, ;; Context
1558 metadata !"", ;; Name
1559 metadata !1, ;; File
1560 i32 0, ;; Line number
1561 i64 32, ;; Size in bits
1562 i64 32, ;; Align in bits
1563 i64 0, ;; Offset in bits
1565 metadata !6 ;; Derived From type
1568 ;; Define the int type.
1572 metadata !1, ;; Context
1573 metadata !"int", ;; Name
1574 metadata !1, ;; File
1575 i32 0, ;; Line number
1576 i64 32, ;; Size in bits
1577 i64 32, ;; Align in bits
1578 i64 0, ;; Offset in bits
1587 <!-- ======================================================================= -->
1588 <div class="doc_subsection">
1589 <a name="ccxx_composite_types">C/C++ struct/union types</a>
1592 <div class="doc_text">
1594 <p>Given the following as an example of C/C++ struct type:</p>
1596 <div class="doc_code">
1606 <p>a C/C++ front-end would generate the following descriptors:</p>
1608 <div class="doc_code">
1611 ;; Define basic type for unsigned int.
1615 metadata !1, ;; Context
1616 metadata !"unsigned int",
1617 metadata !1, ;; File
1618 i32 0, ;; Line number
1619 i64 32, ;; Size in Bits
1620 i64 32, ;; Align in Bits
1621 i64 0, ;; Offset in Bits
1626 ;; Define composite type for struct Color.
1630 metadata !1, ;; Context
1631 metadata !"Color", ;; Name
1632 metadata !1, ;; Compile unit
1633 i32 1, ;; Line number
1634 i64 96, ;; Size in bits
1635 i64 32, ;; Align in bits
1636 i64 0, ;; Offset in bits
1638 null, ;; Derived From
1639 metadata !3, ;; Elements
1640 i32 0 ;; Runtime Language
1644 ;; Define the Red field.
1648 metadata !1, ;; Context
1649 metadata !"Red", ;; Name
1650 metadata !1, ;; File
1651 i32 2, ;; Line number
1652 i64 32, ;; Size in bits
1653 i64 32, ;; Align in bits
1654 i64 0, ;; Offset in bits
1656 metadata !5 ;; Derived From type
1660 ;; Define the Green field.
1664 metadata !1, ;; Context
1665 metadata !"Green", ;; Name
1666 metadata !1, ;; File
1667 i32 3, ;; Line number
1668 i64 32, ;; Size in bits
1669 i64 32, ;; Align in bits
1670 i64 32, ;; Offset in bits
1672 metadata !5 ;; Derived From type
1676 ;; Define the Blue field.
1680 metadata !1, ;; Context
1681 metadata !"Blue", ;; Name
1682 metadata !1, ;; File
1683 i32 4, ;; Line number
1684 i64 32, ;; Size in bits
1685 i64 32, ;; Align in bits
1686 i64 64, ;; Offset in bits
1688 metadata !5 ;; Derived From type
1692 ;; Define the array of fields used by the composite type Color.
1694 !3 = metadata !{metadata !4, metadata !6, metadata !7}
1700 <!-- ======================================================================= -->
1701 <div class="doc_subsection">
1702 <a name="ccxx_enumeration_types">C/C++ enumeration types</a>
1705 <div class="doc_text">
1707 <p>Given the following as an example of C/C++ enumeration type:</p>
1709 <div class="doc_code">
1719 <p>a C/C++ front-end would generate the following descriptors:</p>
1721 <div class="doc_code">
1724 ;; Define composite type for enum Trees
1728 metadata !1, ;; Context
1729 metadata !"Trees", ;; Name
1730 metadata !1, ;; File
1731 i32 1, ;; Line number
1732 i64 32, ;; Size in bits
1733 i64 32, ;; Align in bits
1734 i64 0, ;; Offset in bits
1736 null, ;; Derived From type
1737 metadata !3, ;; Elements
1738 i32 0 ;; Runtime language
1742 ;; Define the array of enumerators used by composite type Trees.
1744 !3 = metadata !{metadata !4, metadata !5, metadata !6}
1747 ;; Define Spruce enumerator.
1749 !4 = metadata !{i32 524328, metadata !"Spruce", i64 100}
1752 ;; Define Oak enumerator.
1754 !5 = metadata !{i32 524328, metadata !"Oak", i64 200}
1757 ;; Define Maple enumerator.
1759 !6 = metadata !{i32 524328, metadata !"Maple", i64 300}
1766 <!-- *********************************************************************** -->
1770 <a href="http://jigsaw.w3.org/css-validator/check/referer"><img
1771 src="http://jigsaw.w3.org/css-validator/images/vcss-blue" alt="Valid CSS"></a>
1772 <a href="http://validator.w3.org/check/referer"><img
1773 src="http://www.w3.org/Icons/valid-html401-blue" alt="Valid HTML 4.01"></a>
1775 <a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
1776 <a href="http://llvm.org">LLVM Compiler Infrastructure</a><br>
1777 Last modified: $Date$