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 <h1>Source Level Debugging with LLVM</h1>
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 <h2><a name="introduction">Introduction</a></h2>
72 <!-- *********************************************************************** -->
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
81 for C/C++ looks like.</p>
83 <!-- ======================================================================= -->
85 <a name="phil">Philosophy behind LLVM debugging information</a>
90 <p>The idea of the LLVM debugging information is to capture how the important
91 pieces of the source-language's Abstract Syntax Tree map onto LLVM code.
92 Several design aspects have shaped the solution that appears here. The
93 important ones are:</p>
96 <li>Debugging information should have very little impact on the rest of the
97 compiler. No transformations, analyses, or code generators should need to
98 be modified because of debugging information.</li>
100 <li>LLVM optimizations should interact in <a href="#debugopt">well-defined and
101 easily described ways</a> with the debugging information.</li>
103 <li>Because LLVM is designed to support arbitrary programming languages,
104 LLVM-to-LLVM tools should not need to know anything about the semantics of
105 the source-level-language.</li>
107 <li>Source-level languages are often <b>widely</b> different from one another.
108 LLVM should not put any restrictions of the flavor of the source-language,
109 and the debugging information should work with any language.</li>
111 <li>With code generator support, it should be possible to use an LLVM compiler
112 to compile a program to native machine code and standard debugging
113 formats. This allows compatibility with traditional machine-code level
114 debuggers, like GDB or DBX.</li>
117 <p>The approach used by the LLVM implementation is to use a small set
118 of <a href="#format_common_intrinsics">intrinsic functions</a> to define a
119 mapping between LLVM program objects and the source-level objects. The
120 description of the source-level program is maintained in LLVM metadata
121 in an <a href="#ccxx_frontend">implementation-defined format</a>
122 (the C/C++ front-end currently uses working draft 7 of
123 the <a href="http://www.eagercon.com/dwarf/dwarf3std.htm">DWARF 3
126 <p>When a program is being debugged, a debugger interacts with the user and
127 turns the stored debug information into source-language specific information.
128 As such, a debugger must be aware of the source-language, and is thus tied to
129 a specific language or family of languages.</p>
133 <!-- ======================================================================= -->
135 <a name="consumers">Debug information consumers</a>
140 <p>The role of debug information is to provide meta information normally
141 stripped away during the compilation process. This meta information provides
142 an LLVM user a relationship between generated code and the original program
145 <p>Currently, debug information is consumed by DwarfDebug to produce dwarf
146 information used by the gdb debugger. Other targets could use the same
147 information to produce stabs or other debug forms.</p>
149 <p>It would also be reasonable to use debug information to feed profiling tools
150 for analysis of generated code, or, tools for reconstructing the original
151 source from generated code.</p>
153 <p>TODO - expound a bit more.</p>
157 <!-- ======================================================================= -->
159 <a name="debugopt">Debugging optimized code</a>
164 <p>An extremely high priority of LLVM debugging information is to make it
165 interact well with optimizations and analysis. In particular, the LLVM debug
166 information provides the following guarantees:</p>
169 <li>LLVM debug information <b>always provides information to accurately read
170 the source-level state of the program</b>, regardless of which LLVM
171 optimizations have been run, and without any modification to the
172 optimizations themselves. However, some optimizations may impact the
173 ability to modify the current state of the program with a debugger, such
174 as setting program variables, or calling functions that have been
177 <li>As desired, LLVM optimizations can be upgraded to be aware of the LLVM
178 debugging information, allowing them to update the debugging information
179 as they perform aggressive optimizations. This means that, with effort,
180 the LLVM optimizers could optimize debug code just as well as non-debug
183 <li>LLVM debug information does not prevent optimizations from
184 happening (for example inlining, basic block reordering/merging/cleanup,
185 tail duplication, etc).</li>
187 <li>LLVM debug information is automatically optimized along with the rest of
188 the program, using existing facilities. For example, duplicate
189 information is automatically merged by the linker, and unused information
190 is automatically removed.</li>
193 <p>Basically, the debug information allows you to compile a program with
194 "<tt>-O0 -g</tt>" and get full debug information, allowing you to arbitrarily
195 modify the program as it executes from a debugger. Compiling a program with
196 "<tt>-O3 -g</tt>" gives you full debug information that is always available
197 and accurate for reading (e.g., you get accurate stack traces despite tail
198 call elimination and inlining), but you might lose the ability to modify the
199 program and call functions where were optimized out of the program, or
200 inlined away completely.</p>
202 <p><a href="TestingGuide.html#quicktestsuite">LLVM test suite</a> provides a
203 framework to test optimizer's handling of debugging information. It can be
206 <div class="doc_code">
208 % cd llvm/projects/test-suite/MultiSource/Benchmarks # or some other level
213 <p>This will test impact of debugging information on optimization passes. If
214 debugging information influences optimization passes then it will be reported
215 as a failure. See <a href="TestingGuide.html">TestingGuide</a> for more
216 information on LLVM test infrastructure and how to run various tests.</p>
222 <!-- *********************************************************************** -->
224 <a name="format">Debugging information format</a>
226 <!-- *********************************************************************** -->
230 <p>LLVM debugging information has been carefully designed to make it possible
231 for the optimizer to optimize the program and debugging information without
232 necessarily having to know anything about debugging information. In
233 particular, the use of metadata avoids duplicated debugging information from
234 the beginning, and the global dead code elimination pass automatically
235 deletes debugging information for a function if it decides to delete the
238 <p>To do this, most of the debugging information (descriptors for types,
239 variables, functions, source files, etc) is inserted by the language
240 front-end in the form of LLVM metadata. </p>
242 <p>Debug information is designed to be agnostic about the target debugger and
243 debugging information representation (e.g. DWARF/Stabs/etc). It uses a
244 generic pass to decode the information that represents variables, types,
245 functions, namespaces, etc: this allows for arbitrary source-language
246 semantics and type-systems to be used, as long as there is a module
247 written for the target debugger to interpret the information. </p>
249 <p>To provide basic functionality, the LLVM debugger does have to make some
250 assumptions about the source-level language being debugged, though it keeps
251 these to a minimum. The only common features that the LLVM debugger assumes
252 exist are <a href="#format_files">source files</a>,
253 and <a href="#format_global_variables">program objects</a>. These abstract
254 objects are used by a debugger to form stack traces, show information about
255 local variables, etc.</p>
257 <p>This section of the documentation first describes the representation aspects
258 common to any source-language. The <a href="#ccxx_frontend">next section</a>
259 describes the data layout conventions used by the C and C++ front-ends.</p>
261 <!-- ======================================================================= -->
263 <a name="debug_info_descriptors">Debug information descriptors</a>
268 <p>In consideration of the complexity and volume of debug information, LLVM
269 provides a specification for well formed debug descriptors. </p>
271 <p>Consumers of LLVM debug information expect the descriptors for program
272 objects to start in a canonical format, but the descriptors can include
273 additional information appended at the end that is source-language
274 specific. All LLVM debugging information is versioned, allowing backwards
275 compatibility in the case that the core structures need to change in some
276 way. Also, all debugging information objects start with a tag to indicate
277 what type of object it is. The source-language is allowed to define its own
278 objects, by using unreserved tag numbers. We recommend using with tags in
279 the range 0x1000 through 0x2000 (there is a defined enum DW_TAG_user_base =
282 <p>The fields of debug descriptors used internally by LLVM
283 are restricted to only the simple data types <tt>i32</tt>, <tt>i1</tt>,
284 <tt>float</tt>, <tt>double</tt>, <tt>mdstring</tt> and <tt>mdnode</tt>. </p>
286 <div class="doc_code">
295 <p><a name="LLVMDebugVersion">The first field of a descriptor is always an
296 <tt>i32</tt> containing a tag value identifying the content of the
297 descriptor. The remaining fields are specific to the descriptor. The values
298 of tags are loosely bound to the tag values of DWARF information entries.
299 However, that does not restrict the use of the information supplied to DWARF
300 targets. To facilitate versioning of debug information, the tag is augmented
301 with the current debug version (LLVMDebugVersion = 8 << 16 or
302 0x80000 or 524288.)</a></p>
304 <p>The details of the various descriptors follow.</p>
306 <!-- ======================================================================= -->
308 <a name="format_compile_units">Compile unit descriptors</a>
313 <div class="doc_code">
316 i32, ;; Tag = 17 + <a href="#LLVMDebugVersion">LLVMDebugVersion</a>
317 ;; (DW_TAG_compile_unit)
318 i32, ;; Unused field.
319 i32, ;; DWARF language identifier (ex. DW_LANG_C89)
320 metadata, ;; Source file name
321 metadata, ;; Source file directory (includes trailing slash)
322 metadata ;; Producer (ex. "4.0.1 LLVM (LLVM research group)")
323 i1, ;; True if this is a main compile unit.
324 i1, ;; True if this is optimized.
326 i32 ;; Runtime version
331 <p>These descriptors contain a source language ID for the file (we use the DWARF
332 3.0 ID numbers, such as <tt>DW_LANG_C89</tt>, <tt>DW_LANG_C_plus_plus</tt>,
333 <tt>DW_LANG_Cobol74</tt>, etc), three strings describing the filename,
334 working directory of the compiler, and an identifier string for the compiler
335 that produced it.</p>
337 <p>Compile unit descriptors provide the root context for objects declared in a
338 specific compilation unit. File descriptors are defined using this context.
339 These descriptors are collected by a named metadata
340 <tt>!llvm.dbg.cu</tt>.
344 <!-- ======================================================================= -->
346 <a name="format_files">File descriptors</a>
351 <div class="doc_code">
354 i32, ;; Tag = 41 + <a href="#LLVMDebugVersion">LLVMDebugVersion</a>
355 ;; (DW_TAG_file_type)
356 metadata, ;; Source file name
357 metadata, ;; Source file directory (includes trailing slash)
358 metadata ;; Reference to compile unit where defined
363 <p>These descriptors contain information for a file. Global variables and top
364 level functions would be defined using this context.k File descriptors also
365 provide context for source line correspondence. </p>
367 <p>Each input file is encoded as a separate file descriptor in LLVM debugging
368 information output. Each file descriptor would be defined using a
373 <!-- ======================================================================= -->
375 <a name="format_global_variables">Global variable descriptors</a>
380 <div class="doc_code">
383 i32, ;; Tag = 52 + <a href="#LLVMDebugVersion">LLVMDebugVersion</a>
385 i32, ;; Unused field.
386 metadata, ;; Reference to context descriptor
388 metadata, ;; Display name (fully qualified C++ name)
389 metadata, ;; MIPS linkage name (for C++)
390 metadata, ;; Reference to file where defined
391 i32, ;; Line number where defined
392 metadata, ;; Reference to type descriptor
393 i1, ;; True if the global is local to compile unit (static)
394 i1, ;; True if the global is defined in the compile unit (not extern)
395 {}* ;; Reference to the global variable
400 <p>These descriptors provide debug information about globals variables. The
401 provide details such as name, type and where the variable is defined. All
402 global variables are collected by named metadata <tt>!llvm.dbg.gv</tt>.</p>
406 <!-- ======================================================================= -->
408 <a name="format_subprograms">Subprogram descriptors</a>
413 <div class="doc_code">
416 i32, ;; Tag = 46 + <a href="#LLVMDebugVersion">LLVMDebugVersion</a>
417 ;; (DW_TAG_subprogram)
418 i32, ;; Unused field.
419 metadata, ;; Reference to context descriptor
421 metadata, ;; Display name (fully qualified C++ name)
422 metadata, ;; MIPS linkage name (for C++)
423 metadata, ;; Reference to file where defined
424 i32, ;; Line number where defined
425 metadata, ;; Reference to type descriptor
426 i1, ;; True if the global is local to compile unit (static)
427 i1, ;; True if the global is defined in the compile unit (not extern)
428 i32, ;; Virtuality, e.g. dwarf::DW_VIRTUALITY__virtual
429 i32, ;; Index into a virtual function
430 metadata, ;; indicates which base type contains the vtable pointer for the
434 Function *,;; Pointer to LLVM function
435 metadata, ;; Lists function template parameters
436 metadata ;; Function declaration descriptor
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.
444 All subprogram descriptors are collected by a named metadata
445 <tt>!llvm.dbg.sp</tt>.
450 <!-- ======================================================================= -->
452 <a name="format_blocks">Block descriptors</a>
457 <div class="doc_code">
460 i32, ;; Tag = 11 + <a href="#LLVMDebugVersion">LLVMDebugVersion</a> (DW_TAG_lexical_block)
461 metadata,;; Reference to context descriptor
463 i32, ;; Column number
464 metadata,;; Reference to source file
465 i32 ;; Unique ID to identify blocks from a template function
470 <p>These descriptors provide debug information about nested blocks within a
471 subprogram. The line number and column numbers are used to dinstinguish
472 two lexical blocks at same depth. </p>
476 <!-- ======================================================================= -->
478 <a name="format_basic_type">Basic type descriptors</a>
483 <div class="doc_code">
486 i32, ;; Tag = 36 + <a href="#LLVMDebugVersion">LLVMDebugVersion</a>
487 ;; (DW_TAG_base_type)
488 metadata, ;; Reference to context (typically a compile unit)
489 metadata, ;; Name (may be "" for anonymous types)
490 metadata, ;; Reference to file where defined (may be NULL)
491 i32, ;; Line number where defined (may be 0)
493 i64, ;; Alignment in bits
494 i64, ;; Offset in bits
496 i32 ;; DWARF type encoding
501 <p>These descriptors define primitive types used in the code. Example int, bool
502 and float. The context provides the scope of the type, which is usually the
503 top level. Since basic types are not usually user defined the compile unit
504 and line number can be left as NULL and 0. The size, alignment and offset
505 are expressed in bits and can be 64 bit values. The alignment is used to
506 round the offset when embedded in a
507 <a href="#format_composite_type">composite type</a> (example to keep float
508 doubles on 64 bit boundaries.) The offset is the bit offset if embedded in
509 a <a href="#format_composite_type">composite type</a>.</p>
511 <p>The type encoding provides the details of the type. The values are typically
512 one of the following:</p>
514 <div class="doc_code">
520 DW_ATE_signed_char = 6
522 DW_ATE_unsigned_char = 8
528 <!-- ======================================================================= -->
530 <a name="format_derived_type">Derived type descriptors</a>
535 <div class="doc_code">
538 i32, ;; Tag (see below)
539 metadata, ;; Reference to context
540 metadata, ;; Name (may be "" for anonymous types)
541 metadata, ;; Reference to file where defined (may be NULL)
542 i32, ;; Line number where defined (may be 0)
544 i64, ;; Alignment in bits
545 i64, ;; Offset in bits
546 metadata, ;; Reference to type derived from
547 metadata, ;; (optional) Name of the Objective C property assoicated with
548 ;; Objective-C an ivar
549 metadata, ;; (optional) Name of the Objective C property getter selector.
550 metadata, ;; (optional) Name of the Objective C property setter selector.
551 i32 ;; (optional) Objective C property attributes.
556 <p>These descriptors are used to define types derived from other types. The
557 value of the tag varies depending on the meaning. The following are possible
560 <div class="doc_code">
562 DW_TAG_formal_parameter = 5
564 DW_TAG_pointer_type = 15
565 DW_TAG_reference_type = 16
567 DW_TAG_const_type = 38
568 DW_TAG_volatile_type = 53
569 DW_TAG_restrict_type = 55
573 <p><tt>DW_TAG_member</tt> is used to define a member of
574 a <a href="#format_composite_type">composite type</a>
575 or <a href="#format_subprograms">subprogram</a>. The type of the member is
576 the <a href="#format_derived_type">derived
577 type</a>. <tt>DW_TAG_formal_parameter</tt> is used to define a member which
578 is a formal argument of a subprogram.</p>
580 <p><tt>DW_TAG_typedef</tt> is used to provide a name for the derived type.</p>
582 <p><tt>DW_TAG_pointer_type</tt>,<tt>DW_TAG_reference_type</tt>,
583 <tt>DW_TAG_const_type</tt>, <tt>DW_TAG_volatile_type</tt>
584 and <tt>DW_TAG_restrict_type</tt> are used to qualify
585 the <a href="#format_derived_type">derived type</a>. </p>
587 <p><a href="#format_derived_type">Derived type</a> location can be determined
588 from the compile unit and line number. The size, alignment and offset are
589 expressed in bits and can be 64 bit values. The alignment is used to round
590 the offset when embedded in a <a href="#format_composite_type">composite
591 type</a> (example to keep float doubles on 64 bit boundaries.) The offset is
592 the bit offset if embedded in a <a href="#format_composite_type">composite
595 <p>Note that the <tt>void *</tt> type is expressed as a type derived from NULL.
600 <!-- ======================================================================= -->
602 <a name="format_composite_type">Composite type descriptors</a>
607 <div class="doc_code">
610 i32, ;; Tag (see below)
611 metadata, ;; Reference to context
612 metadata, ;; Name (may be "" for anonymous types)
613 metadata, ;; Reference to file where defined (may be NULL)
614 i32, ;; Line number where defined (may be 0)
616 i64, ;; Alignment in bits
617 i64, ;; Offset in bits
619 metadata, ;; Reference to type derived from
620 metadata, ;; Reference to array of member descriptors
621 i32 ;; Runtime languages
626 <p>These descriptors are used to define types that are composed of 0 or more
627 elements. The value of the tag varies depending on the meaning. The following
628 are possible tag values:</p>
630 <div class="doc_code">
632 DW_TAG_array_type = 1
633 DW_TAG_enumeration_type = 4
634 DW_TAG_structure_type = 19
635 DW_TAG_union_type = 23
636 DW_TAG_vector_type = 259
637 DW_TAG_subroutine_type = 21
638 DW_TAG_inheritance = 28
642 <p>The vector flag indicates that an array type is a native packed vector.</p>
644 <p>The members of array types (tag = <tt>DW_TAG_array_type</tt>) or vector types
645 (tag = <tt>DW_TAG_vector_type</tt>) are <a href="#format_subrange">subrange
646 descriptors</a>, each representing the range of subscripts at that level of
649 <p>The members of enumeration types (tag = <tt>DW_TAG_enumeration_type</tt>) are
650 <a href="#format_enumeration">enumerator descriptors</a>, each representing
651 the definition of enumeration value for the set. All enumeration type
652 descriptors are collected by named metadata <tt>!llvm.dbg.enum</tt>.</p>
654 <p>The members of structure (tag = <tt>DW_TAG_structure_type</tt>) or union (tag
655 = <tt>DW_TAG_union_type</tt>) types are any one of
656 the <a href="#format_basic_type">basic</a>,
657 <a href="#format_derived_type">derived</a>
658 or <a href="#format_composite_type">composite</a> type descriptors, each
659 representing a field member of the structure or union.</p>
661 <p>For C++ classes (tag = <tt>DW_TAG_structure_type</tt>), member descriptors
662 provide information about base classes, static members and member
663 functions. If a member is a <a href="#format_derived_type">derived type
664 descriptor</a> and has a tag of <tt>DW_TAG_inheritance</tt>, then the type
665 represents a base class. If the member of is
666 a <a href="#format_global_variables">global variable descriptor</a> then it
667 represents a static member. And, if the member is
668 a <a href="#format_subprograms">subprogram descriptor</a> then it represents
669 a member function. For static members and member
670 functions, <tt>getName()</tt> returns the members link or the C++ mangled
671 name. <tt>getDisplayName()</tt> the simplied version of the name.</p>
673 <p>The first member of subroutine (tag = <tt>DW_TAG_subroutine_type</tt>) type
674 elements is the return type for the subroutine. The remaining elements are
675 the formal arguments to the subroutine.</p>
677 <p><a href="#format_composite_type">Composite type</a> location can be
678 determined from the compile unit and line number. The size, alignment and
679 offset are expressed in bits and can be 64 bit values. The alignment is used
680 to round the offset when embedded in
681 a <a href="#format_composite_type">composite type</a> (as an example, to keep
682 float doubles on 64 bit boundaries.) The offset is the bit offset if embedded
683 in a <a href="#format_composite_type">composite type</a>.</p>
687 <!-- ======================================================================= -->
689 <a name="format_subrange">Subrange descriptors</a>
694 <div class="doc_code">
697 i32, ;; Tag = 33 + <a href="#LLVMDebugVersion">LLVMDebugVersion</a> (DW_TAG_subrange_type)
704 <p>These descriptors are used to define ranges of array subscripts for an array
705 <a href="#format_composite_type">composite type</a>. The low value defines
706 the lower bounds typically zero for C/C++. The high value is the upper
707 bounds. Values are 64 bit. High - low + 1 is the size of the array. If low
708 > high the array bounds are not included in generated debugging information.
713 <!-- ======================================================================= -->
715 <a name="format_enumeration">Enumerator descriptors</a>
720 <div class="doc_code">
723 i32, ;; Tag = 40 + <a href="#LLVMDebugVersion">LLVMDebugVersion</a>
724 ;; (DW_TAG_enumerator)
731 <p>These descriptors are used to define members of an
732 enumeration <a href="#format_composite_type">composite type</a>, it
733 associates the name to the value.</p>
737 <!-- ======================================================================= -->
739 <a name="format_variables">Local variables</a>
744 <div class="doc_code">
747 i32, ;; Tag (see below)
750 metadata, ;; Reference to file where defined
751 i32, ;; 24 bit - Line number where defined
752 ;; 8 bit - Argument number. 1 indicates 1st argument.
753 metadata, ;; Type descriptor
755 metadata ;; (optional) Reference to inline location
760 <p>These descriptors are used to define variables local to a sub program. The
761 value of the tag depends on the usage of the variable:</p>
763 <div class="doc_code">
765 DW_TAG_auto_variable = 256
766 DW_TAG_arg_variable = 257
767 DW_TAG_return_variable = 258
771 <p>An auto variable is any variable declared in the body of the function. An
772 argument variable is any variable that appears as a formal argument to the
773 function. A return variable is used to track the result of a function and
774 has no source correspondent.</p>
776 <p>The context is either the subprogram or block where the variable is defined.
777 Name the source variable name. Compile unit and line indicate where the
778 variable was defined. Type descriptor defines the declared type of the
785 <!-- ======================================================================= -->
787 <a name="format_common_intrinsics">Debugger intrinsic functions</a>
792 <p>LLVM uses several intrinsic functions (name prefixed with "llvm.dbg") to
793 provide debug information at various points in generated code.</p>
795 <!-- ======================================================================= -->
797 <a name="format_common_declare">llvm.dbg.declare</a>
802 void %<a href="#format_common_declare">llvm.dbg.declare</a>(metadata, metadata)
805 <p>This intrinsic provides information about a local element (ex. variable.) The
806 first argument is metadata holding alloca for the variable. The
807 second argument is metadata containing description of the variable. </p>
810 <!-- ======================================================================= -->
812 <a name="format_common_value">llvm.dbg.value</a>
817 void %<a href="#format_common_value">llvm.dbg.value</a>(metadata, i64, metadata)
820 <p>This intrinsic provides information when a user source variable is set to a
821 new value. The first argument is the new value (wrapped as metadata). The
822 second argument is the offset in the user source variable where the new value
823 is written. The third argument is metadata containing description of the
824 user source variable. </p>
829 <!-- ======================================================================= -->
831 <a name="format_common_lifetime">Object lifetimes and scoping</a>
835 <p>In many languages, the local variables in functions can have their lifetimes
836 or scopes limited to a subset of a function. In the C family of languages,
837 for example, variables are only live (readable and writable) within the
838 source block that they are defined in. In functional languages, values are
839 only readable after they have been defined. Though this is a very obvious
840 concept, it is non-trivial to model in LLVM, because it has no notion of
841 scoping in this sense, and does not want to be tied to a language's scoping
844 <p>In order to handle this, the LLVM debug format uses the metadata attached to
845 llvm instructions to encode line number and scoping information. Consider
846 the following C fragment, for example:</p>
848 <div class="doc_code">
862 <p>Compiled to LLVM, this function would be represented like this:</p>
864 <div class="doc_code">
866 define void @foo() nounwind ssp {
868 %X = alloca i32, align 4 ; <i32*> [#uses=4]
869 %Y = alloca i32, align 4 ; <i32*> [#uses=4]
870 %Z = alloca i32, align 4 ; <i32*> [#uses=3]
871 %0 = bitcast i32* %X to {}* ; <{}*> [#uses=1]
872 call void @llvm.dbg.declare(metadata !{i32 * %X}, metadata !0), !dbg !7
873 store i32 21, i32* %X, !dbg !8
874 %1 = bitcast i32* %Y to {}* ; <{}*> [#uses=1]
875 call void @llvm.dbg.declare(metadata !{i32 * %Y}, metadata !9), !dbg !10
876 store i32 22, i32* %Y, !dbg !11
877 %2 = bitcast i32* %Z to {}* ; <{}*> [#uses=1]
878 call void @llvm.dbg.declare(metadata !{i32 * %Z}, metadata !12), !dbg !14
879 store i32 23, i32* %Z, !dbg !15
880 %tmp = load i32* %X, !dbg !16 ; <i32> [#uses=1]
881 %tmp1 = load i32* %Y, !dbg !16 ; <i32> [#uses=1]
882 %add = add nsw i32 %tmp, %tmp1, !dbg !16 ; <i32> [#uses=1]
883 store i32 %add, i32* %Z, !dbg !16
884 %tmp2 = load i32* %Y, !dbg !17 ; <i32> [#uses=1]
885 store i32 %tmp2, i32* %X, !dbg !17
889 declare void @llvm.dbg.declare(metadata, metadata) nounwind readnone
891 !0 = metadata !{i32 459008, metadata !1, metadata !"X",
892 metadata !3, i32 2, metadata !6}; [ DW_TAG_auto_variable ]
893 !1 = metadata !{i32 458763, metadata !2}; [DW_TAG_lexical_block ]
894 !2 = metadata !{i32 458798, i32 0, metadata !3, metadata !"foo", metadata !"foo",
895 metadata !"foo", metadata !3, i32 1, metadata !4,
896 i1 false, i1 true}; [DW_TAG_subprogram ]
897 !3 = metadata !{i32 458769, i32 0, i32 12, metadata !"foo.c",
898 metadata !"/private/tmp", metadata !"clang 1.1", i1 true,
899 i1 false, metadata !"", i32 0}; [DW_TAG_compile_unit ]
900 !4 = metadata !{i32 458773, metadata !3, metadata !"", null, i32 0, i64 0, i64 0,
901 i64 0, i32 0, null, metadata !5, i32 0}; [DW_TAG_subroutine_type ]
902 !5 = metadata !{null}
903 !6 = metadata !{i32 458788, metadata !3, metadata !"int", metadata !3, i32 0,
904 i64 32, i64 32, i64 0, i32 0, i32 5}; [DW_TAG_base_type ]
905 !7 = metadata !{i32 2, i32 7, metadata !1, null}
906 !8 = metadata !{i32 2, i32 3, metadata !1, null}
907 !9 = metadata !{i32 459008, metadata !1, metadata !"Y", metadata !3, i32 3,
908 metadata !6}; [ DW_TAG_auto_variable ]
909 !10 = metadata !{i32 3, i32 7, metadata !1, null}
910 !11 = metadata !{i32 3, i32 3, metadata !1, null}
911 !12 = metadata !{i32 459008, metadata !13, metadata !"Z", metadata !3, i32 5,
912 metadata !6}; [ DW_TAG_auto_variable ]
913 !13 = metadata !{i32 458763, metadata !1}; [DW_TAG_lexical_block ]
914 !14 = metadata !{i32 5, i32 9, metadata !13, null}
915 !15 = metadata !{i32 5, i32 5, metadata !13, null}
916 !16 = metadata !{i32 6, i32 5, metadata !13, null}
917 !17 = metadata !{i32 8, i32 3, metadata !1, null}
918 !18 = metadata !{i32 9, i32 1, metadata !2, null}
922 <p>This example illustrates a few important details about LLVM debugging
923 information. In particular, it shows how the <tt>llvm.dbg.declare</tt>
924 intrinsic and location information, which are attached to an instruction,
925 are applied together to allow a debugger to analyze the relationship between
926 statements, variable definitions, and the code used to implement the
929 <div class="doc_code">
931 call void @llvm.dbg.declare(metadata, metadata !0), !dbg !7
935 <p>The first intrinsic
936 <tt>%<a href="#format_common_declare">llvm.dbg.declare</a></tt>
937 encodes debugging information for the variable <tt>X</tt>. The metadata
938 <tt>!dbg !7</tt> attached to the intrinsic provides scope information for the
939 variable <tt>X</tt>.</p>
941 <div class="doc_code">
943 !7 = metadata !{i32 2, i32 7, metadata !1, null}
944 !1 = metadata !{i32 458763, metadata !2}; [DW_TAG_lexical_block ]
945 !2 = metadata !{i32 458798, i32 0, metadata !3, metadata !"foo",
946 metadata !"foo", metadata !"foo", metadata !3, i32 1,
947 metadata !4, i1 false, i1 true}; [DW_TAG_subprogram ]
951 <p>Here <tt>!7</tt> is metadata providing location information. It has four
952 fields: line number, column number, scope, and original scope. The original
953 scope represents inline location if this instruction is inlined inside a
954 caller, and is null otherwise. In this example, scope is encoded by
955 <tt>!1</tt>. <tt>!1</tt> represents a lexical block inside the scope
956 <tt>!2</tt>, where <tt>!2</tt> is a
957 <a href="#format_subprograms">subprogram descriptor</a>. This way the
958 location information attached to the intrinsics indicates that the
959 variable <tt>X</tt> is declared at line number 2 at a function level scope in
960 function <tt>foo</tt>.</p>
962 <p>Now lets take another example.</p>
964 <div class="doc_code">
966 call void @llvm.dbg.declare(metadata, metadata !12), !dbg !14
970 <p>The second intrinsic
971 <tt>%<a href="#format_common_declare">llvm.dbg.declare</a></tt>
972 encodes debugging information for variable <tt>Z</tt>. The metadata
973 <tt>!dbg !14</tt> attached to the intrinsic provides scope information for
974 the variable <tt>Z</tt>.</p>
976 <div class="doc_code">
978 !13 = metadata !{i32 458763, metadata !1}; [DW_TAG_lexical_block ]
979 !14 = metadata !{i32 5, i32 9, metadata !13, null}
983 <p>Here <tt>!14</tt> indicates that <tt>Z</tt> is declared at line number 5 and
984 column number 9 inside of lexical scope <tt>!13</tt>. The lexical scope
985 itself resides inside of lexical scope <tt>!1</tt> described above.</p>
987 <p>The scope information attached with each instruction provides a
988 straightforward way to find instructions covered by a scope.</p>
994 <!-- *********************************************************************** -->
996 <a name="ccxx_frontend">C/C++ front-end specific debug information</a>
998 <!-- *********************************************************************** -->
1002 <p>The C and C++ front-ends represent information about the program in a format
1003 that is effectively identical
1004 to <a href="http://www.eagercon.com/dwarf/dwarf3std.htm">DWARF 3.0</a> in
1005 terms of information content. This allows code generators to trivially
1006 support native debuggers by generating standard dwarf information, and
1007 contains enough information for non-dwarf targets to translate it as
1010 <p>This section describes the forms used to represent C and C++ programs. Other
1011 languages could pattern themselves after this (which itself is tuned to
1012 representing programs in the same way that DWARF 3 does), or they could
1013 choose to provide completely different forms if they don't fit into the DWARF
1014 model. As support for debugging information gets added to the various LLVM
1015 source-language front-ends, the information used should be documented
1018 <p>The following sections provide examples of various C/C++ constructs and the
1019 debug information that would best describe those constructs.</p>
1021 <!-- ======================================================================= -->
1023 <a name="ccxx_compile_units">C/C++ source file information</a>
1028 <p>Given the source files <tt>MySource.cpp</tt> and <tt>MyHeader.h</tt> located
1029 in the directory <tt>/Users/mine/sources</tt>, the following code:</p>
1031 <div class="doc_code">
1033 #include "MyHeader.h"
1035 int main(int argc, char *argv[]) {
1041 <p>a C/C++ front-end would generate the following descriptors:</p>
1043 <div class="doc_code">
1047 ;; Define the compile unit for the main source file "/Users/mine/sources/MySource.cpp".
1052 i32 4, ;; Language Id
1053 metadata !"MySource.cpp",
1054 metadata !"/Users/mine/sources",
1055 metadata !"4.2.1 (Based on Apple Inc. build 5649) (LLVM build 00)",
1056 i1 true, ;; Main Compile Unit
1057 i1 false, ;; Optimized compile unit
1058 metadata !"", ;; Compiler flags
1059 i32 0} ;; Runtime version
1062 ;; Define the file for the file "/Users/mine/sources/MySource.cpp".
1066 metadata !"MySource.cpp",
1067 metadata !"/Users/mine/sources",
1068 metadata !2 ;; Compile unit
1072 ;; Define the file for the file "/Users/mine/sources/Myheader.h"
1076 metadata !"Myheader.h"
1077 metadata !"/Users/mine/sources",
1078 metadata !2 ;; Compile unit
1085 <p>llvm::Instruction provides easy access to metadata attached with an
1086 instruction. One can extract line number information encoded in LLVM IR
1087 using <tt>Instruction::getMetadata()</tt> and
1088 <tt>DILocation::getLineNumber()</tt>.
1090 if (MDNode *N = I->getMetadata("dbg")) { // Here I is an LLVM instruction
1091 DILocation Loc(N); // DILocation is in DebugInfo.h
1092 unsigned Line = Loc.getLineNumber();
1093 StringRef File = Loc.getFilename();
1094 StringRef Dir = Loc.getDirectory();
1099 <!-- ======================================================================= -->
1101 <a name="ccxx_global_variable">C/C++ global variable information</a>
1106 <p>Given an integer global variable declared as follows:</p>
1108 <div class="doc_code">
1114 <p>a C/C++ front-end would generate the following descriptors:</p>
1116 <div class="doc_code">
1119 ;; Define the global itself.
1121 %MyGlobal = global int 100
1124 ;; List of debug info of globals
1126 !llvm.dbg.gv = !{!0}
1129 ;; Define the global variable descriptor. Note the reference to the global
1130 ;; variable anchor and the global variable itself.
1135 metadata !1, ;; Context
1136 metadata !"MyGlobal", ;; Name
1137 metadata !"MyGlobal", ;; Display Name
1138 metadata !"MyGlobal", ;; Linkage Name
1139 metadata !3, ;; Compile Unit
1140 i32 1, ;; Line Number
1141 metadata !4, ;; Type
1142 i1 false, ;; Is a local variable
1143 i1 true, ;; Is this a definition
1144 i32* @MyGlobal ;; The global variable
1148 ;; Define the basic type of 32 bit signed integer. Note that since int is an
1149 ;; intrinsic type the source file is NULL and line 0.
1153 metadata !1, ;; Context
1154 metadata !"int", ;; Name
1155 metadata !1, ;; File
1156 i32 0, ;; Line number
1157 i64 32, ;; Size in Bits
1158 i64 32, ;; Align in Bits
1159 i64 0, ;; Offset in Bits
1169 <!-- ======================================================================= -->
1171 <a name="ccxx_subprogram">C/C++ function information</a>
1176 <p>Given a function declared as follows:</p>
1178 <div class="doc_code">
1180 int main(int argc, char *argv[]) {
1186 <p>a C/C++ front-end would generate the following descriptors:</p>
1188 <div class="doc_code">
1191 ;; Define the anchor for subprograms. Note that the second field of the
1192 ;; anchor is 46, which is the same as the tag for subprograms
1193 ;; (46 = DW_TAG_subprogram.)
1198 metadata !1, ;; Context
1199 metadata !"main", ;; Name
1200 metadata !"main", ;; Display name
1201 metadata !"main", ;; Linkage name
1202 metadata !1, ;; File
1203 i32 1, ;; Line number
1204 metadata !4, ;; Type
1205 i1 false, ;; Is local
1206 i1 true, ;; Is definition
1207 i32 0, ;; Virtuality attribute, e.g. pure virtual function
1208 i32 0, ;; Index into virtual table for C++ methods
1209 i32 0, ;; Type that holds virtual table.
1211 i1 false, ;; True if this function is optimized
1212 Function *, ;; Pointer to llvm::Function
1213 null ;; Function template parameters
1216 ;; Define the subprogram itself.
1218 define i32 @main(i32 %argc, i8** %argv) {
1226 <!-- ======================================================================= -->
1228 <a name="ccxx_basic_types">C/C++ basic types</a>
1233 <p>The following are the basic type descriptors for C/C++ core types:</p>
1235 <!-- ======================================================================= -->
1237 <a name="ccxx_basic_type_bool">bool</a>
1242 <div class="doc_code">
1246 metadata !1, ;; Context
1247 metadata !"bool", ;; Name
1248 metadata !1, ;; File
1249 i32 0, ;; Line number
1250 i64 8, ;; Size in Bits
1251 i64 8, ;; Align in Bits
1252 i64 0, ;; Offset in Bits
1261 <!-- ======================================================================= -->
1263 <a name="ccxx_basic_char">char</a>
1268 <div class="doc_code">
1272 metadata !1, ;; Context
1273 metadata !"char", ;; Name
1274 metadata !1, ;; File
1275 i32 0, ;; Line number
1276 i64 8, ;; Size in Bits
1277 i64 8, ;; Align in Bits
1278 i64 0, ;; Offset in Bits
1287 <!-- ======================================================================= -->
1289 <a name="ccxx_basic_unsigned_char">unsigned char</a>
1294 <div class="doc_code">
1298 metadata !1, ;; Context
1299 metadata !"unsigned char",
1300 metadata !1, ;; File
1301 i32 0, ;; Line number
1302 i64 8, ;; Size in Bits
1303 i64 8, ;; Align in Bits
1304 i64 0, ;; Offset in Bits
1313 <!-- ======================================================================= -->
1315 <a name="ccxx_basic_short">short</a>
1320 <div class="doc_code">
1324 metadata !1, ;; Context
1325 metadata !"short int",
1326 metadata !1, ;; File
1327 i32 0, ;; Line number
1328 i64 16, ;; Size in Bits
1329 i64 16, ;; Align in Bits
1330 i64 0, ;; Offset in Bits
1339 <!-- ======================================================================= -->
1341 <a name="ccxx_basic_unsigned_short">unsigned short</a>
1346 <div class="doc_code">
1350 metadata !1, ;; Context
1351 metadata !"short unsigned int",
1352 metadata !1, ;; File
1353 i32 0, ;; Line number
1354 i64 16, ;; Size in Bits
1355 i64 16, ;; Align in Bits
1356 i64 0, ;; Offset in Bits
1365 <!-- ======================================================================= -->
1367 <a name="ccxx_basic_int">int</a>
1372 <div class="doc_code">
1376 metadata !1, ;; Context
1377 metadata !"int", ;; Name
1378 metadata !1, ;; File
1379 i32 0, ;; Line number
1380 i64 32, ;; Size in Bits
1381 i64 32, ;; Align in Bits
1382 i64 0, ;; Offset in Bits
1390 <!-- ======================================================================= -->
1392 <a name="ccxx_basic_unsigned_int">unsigned int</a>
1397 <div class="doc_code">
1401 metadata !1, ;; Context
1402 metadata !"unsigned int",
1403 metadata !1, ;; File
1404 i32 0, ;; Line number
1405 i64 32, ;; Size in Bits
1406 i64 32, ;; Align in Bits
1407 i64 0, ;; Offset in Bits
1416 <!-- ======================================================================= -->
1418 <a name="ccxx_basic_long_long">long long</a>
1423 <div class="doc_code">
1427 metadata !1, ;; Context
1428 metadata !"long long int",
1429 metadata !1, ;; File
1430 i32 0, ;; Line number
1431 i64 64, ;; Size in Bits
1432 i64 64, ;; Align in Bits
1433 i64 0, ;; Offset in Bits
1442 <!-- ======================================================================= -->
1444 <a name="ccxx_basic_unsigned_long_long">unsigned long long</a>
1449 <div class="doc_code">
1453 metadata !1, ;; Context
1454 metadata !"long long unsigned int",
1455 metadata !1, ;; File
1456 i32 0, ;; Line number
1457 i64 64, ;; Size in Bits
1458 i64 64, ;; Align in Bits
1459 i64 0, ;; Offset in Bits
1468 <!-- ======================================================================= -->
1470 <a name="ccxx_basic_float">float</a>
1475 <div class="doc_code">
1479 metadata !1, ;; Context
1481 metadata !1, ;; File
1482 i32 0, ;; Line number
1483 i64 32, ;; Size in Bits
1484 i64 32, ;; Align in Bits
1485 i64 0, ;; Offset in Bits
1494 <!-- ======================================================================= -->
1496 <a name="ccxx_basic_double">double</a>
1501 <div class="doc_code">
1505 metadata !1, ;; Context
1506 metadata !"double",;; Name
1507 metadata !1, ;; File
1508 i32 0, ;; Line number
1509 i64 64, ;; Size in Bits
1510 i64 64, ;; Align in Bits
1511 i64 0, ;; Offset in Bits
1522 <!-- ======================================================================= -->
1524 <a name="ccxx_derived_types">C/C++ derived types</a>
1529 <p>Given the following as an example of C/C++ derived type:</p>
1531 <div class="doc_code">
1533 typedef const int *IntPtr;
1537 <p>a C/C++ front-end would generate the following descriptors:</p>
1539 <div class="doc_code">
1542 ;; Define the typedef "IntPtr".
1546 metadata !1, ;; Context
1547 metadata !"IntPtr", ;; Name
1548 metadata !3, ;; File
1549 i32 0, ;; Line number
1550 i64 0, ;; Size in bits
1551 i64 0, ;; Align in bits
1552 i64 0, ;; Offset in bits
1554 metadata !4 ;; Derived From type
1558 ;; Define the pointer type.
1562 metadata !1, ;; Context
1563 metadata !"", ;; Name
1564 metadata !1, ;; File
1565 i32 0, ;; Line number
1566 i64 64, ;; Size in bits
1567 i64 64, ;; Align in bits
1568 i64 0, ;; Offset in bits
1570 metadata !5 ;; Derived From type
1573 ;; Define the const type.
1577 metadata !1, ;; Context
1578 metadata !"", ;; Name
1579 metadata !1, ;; File
1580 i32 0, ;; Line number
1581 i64 32, ;; Size in bits
1582 i64 32, ;; Align in bits
1583 i64 0, ;; Offset in bits
1585 metadata !6 ;; Derived From type
1588 ;; Define the int type.
1592 metadata !1, ;; Context
1593 metadata !"int", ;; Name
1594 metadata !1, ;; File
1595 i32 0, ;; Line number
1596 i64 32, ;; Size in bits
1597 i64 32, ;; Align in bits
1598 i64 0, ;; Offset in bits
1607 <!-- ======================================================================= -->
1609 <a name="ccxx_composite_types">C/C++ struct/union types</a>
1614 <p>Given the following as an example of C/C++ struct type:</p>
1616 <div class="doc_code">
1626 <p>a C/C++ front-end would generate the following descriptors:</p>
1628 <div class="doc_code">
1631 ;; Define basic type for unsigned int.
1635 metadata !1, ;; Context
1636 metadata !"unsigned int",
1637 metadata !1, ;; File
1638 i32 0, ;; Line number
1639 i64 32, ;; Size in Bits
1640 i64 32, ;; Align in Bits
1641 i64 0, ;; Offset in Bits
1646 ;; Define composite type for struct Color.
1650 metadata !1, ;; Context
1651 metadata !"Color", ;; Name
1652 metadata !1, ;; Compile unit
1653 i32 1, ;; Line number
1654 i64 96, ;; Size in bits
1655 i64 32, ;; Align in bits
1656 i64 0, ;; Offset in bits
1658 null, ;; Derived From
1659 metadata !3, ;; Elements
1660 i32 0 ;; Runtime Language
1664 ;; Define the Red field.
1668 metadata !1, ;; Context
1669 metadata !"Red", ;; Name
1670 metadata !1, ;; File
1671 i32 2, ;; Line number
1672 i64 32, ;; Size in bits
1673 i64 32, ;; Align in bits
1674 i64 0, ;; Offset in bits
1676 metadata !5 ;; Derived From type
1680 ;; Define the Green field.
1684 metadata !1, ;; Context
1685 metadata !"Green", ;; Name
1686 metadata !1, ;; File
1687 i32 3, ;; Line number
1688 i64 32, ;; Size in bits
1689 i64 32, ;; Align in bits
1690 i64 32, ;; Offset in bits
1692 metadata !5 ;; Derived From type
1696 ;; Define the Blue field.
1700 metadata !1, ;; Context
1701 metadata !"Blue", ;; Name
1702 metadata !1, ;; File
1703 i32 4, ;; Line number
1704 i64 32, ;; Size in bits
1705 i64 32, ;; Align in bits
1706 i64 64, ;; Offset in bits
1708 metadata !5 ;; Derived From type
1712 ;; Define the array of fields used by the composite type Color.
1714 !3 = metadata !{metadata !4, metadata !6, metadata !7}
1720 <!-- ======================================================================= -->
1722 <a name="ccxx_enumeration_types">C/C++ enumeration types</a>
1727 <p>Given the following as an example of C/C++ enumeration type:</p>
1729 <div class="doc_code">
1739 <p>a C/C++ front-end would generate the following descriptors:</p>
1741 <div class="doc_code">
1744 ;; Define composite type for enum Trees
1748 metadata !1, ;; Context
1749 metadata !"Trees", ;; Name
1750 metadata !1, ;; File
1751 i32 1, ;; Line number
1752 i64 32, ;; Size in bits
1753 i64 32, ;; Align in bits
1754 i64 0, ;; Offset in bits
1756 null, ;; Derived From type
1757 metadata !3, ;; Elements
1758 i32 0 ;; Runtime language
1762 ;; Define the array of enumerators used by composite type Trees.
1764 !3 = metadata !{metadata !4, metadata !5, metadata !6}
1767 ;; Define Spruce enumerator.
1769 !4 = metadata !{i32 524328, metadata !"Spruce", i64 100}
1772 ;; Define Oak enumerator.
1774 !5 = metadata !{i32 524328, metadata !"Oak", i64 200}
1777 ;; Define Maple enumerator.
1779 !6 = metadata !{i32 524328, metadata !"Maple", i64 300}
1788 <!-- *********************************************************************** -->
1792 <a href="http://jigsaw.w3.org/css-validator/check/referer"><img
1793 src="http://jigsaw.w3.org/css-validator/images/vcss-blue" alt="Valid CSS"></a>
1794 <a href="http://validator.w3.org/check/referer"><img
1795 src="http://www.w3.org/Icons/valid-html401-blue" alt="Valid HTML 4.01"></a>
1797 <a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
1798 <a href="http://llvm.org/">LLVM Compiler Infrastructure</a><br>
1799 Last modified: $Date$