X-Git-Url: http://demsky.eecs.uci.edu/git/?a=blobdiff_plain;f=docs%2FSourceLevelDebugging.html;h=f1e1cd0285d88d2d11cf6cdd2529aa5772656b79;hb=3d793962becf3a345cfff96202f3c6c27a1fb5d4;hp=9e919bc2985df38eb92130c9cb4a6be3922959d1;hpb=789b45b066d3e0cbaec71aa1b8defd8fe7a55a36;p=oota-llvm.git diff --git a/docs/SourceLevelDebugging.html b/docs/SourceLevelDebugging.html index 9e919bc2985..f1e1cd0285d 100644 --- a/docs/SourceLevelDebugging.html +++ b/docs/SourceLevelDebugging.html @@ -25,6 +25,7 @@
  • Debug information descriptors
  • Debugger intrinsic functions
  • -
  • Representing stopping points in the - source program
  • +
  • Object lifetimes and scoping
  • C/C++ front-end specific debug information
    1. C/C++ source file information
    2. @@ -81,7 +78,7 @@ height="369"> that the LLVM debug information takes, which is useful for those interested in creating front-ends or dealing directly with the information. Further, this document provides specific examples of what debug information - for C/C++.

      + for C/C++ looks like.

      @@ -147,7 +144,7 @@ height="369"> an LLVM user a relationship between generated code and the original program source code.

      -

      Currently, debug information is consumed by the DwarfWriter to produce dwarf +

      Currently, debug information is consumed by DwarfDebug to produce dwarf information used by the gdb debugger. Other targets could use the same information to produce stabs or other debug forms.

      @@ -240,7 +237,7 @@ height="369">

      LLVM debugging information has been carefully designed to make it possible for the optimizer to optimize the program and debugging information without necessarily having to know anything about debugging information. In - particular, te use of metadadta avoids duplicated dubgging information from + particular, the use of metadata avoids duplicated debugging information from the beginning, and the global dead code elimination pass automatically deletes debugging information for a function if it decides to delete the function.

      @@ -259,7 +256,7 @@ height="369">

      To provide basic functionality, the LLVM debugger does have to make some assumptions about the source-level language being debugged, though it keeps these to a minimum. The only common features that the LLVM debugger assumes - exist are source files, + exist are source files, and program objects. These abstract objects are used by a debugger to form stack traces, show information about local variables, etc.

      @@ -292,27 +289,26 @@ height="369"> 0x1000.)

      The fields of debug descriptors used internally by LLVM - are restricted to only the simple data types int, uint, - bool, float, double, mdstring and - mdnode.

      + are restricted to only the simple data types i32, i1, + float, double, mdstring and mdnode.

       !1 = metadata !{
      -  uint,   ;; A tag
      +  i32,   ;; A tag
         ...
       }
       

      The first field of a descriptor is always an - uint containing a tag value identifying the content of the + i32 containing a tag value identifying the content of the descriptor. The remaining fields are specific to the descriptor. The values of tags are loosely bound to the tag values of DWARF information entries. However, that does not restrict the use of the information supplied to DWARF targets. To facilitate versioning of debug information, the tag is augmented - with the current debug version (LLVMDebugVersion = 7 << 16 or 0x70000 or - 458752.)

      + with the current debug version (LLVMDebugVersion = 8 << 16 or 0x80000 or + 524288.)

      The details of the various descriptors follow.

      @@ -350,18 +346,36 @@ height="369"> that produced it.

      Compile unit descriptors provide the root context for objects declared in a - specific source file. Global variables and top level functions would be - defined using this context. Compile unit descriptors also provide context - for source line correspondence.

      + specific compilation unit. File descriptors are defined using this context.

      -

      Each input file is encoded as a separate compile unit in LLVM debugging - information output. However, many target specific tool chains prefer to - encode only one compile unit in an object file. In this situation, the LLVM - code generator will include debugging information entities in the compile - unit that is marked as main compile unit. The code generator accepts maximum - one main compile unit per module. If a module does not contain any main - compile unit then the code generator will emit multiple compile units in the - output object file.

      + + + + + +
      + +
      +
      +!0 = metadata !{
      +  i32,       ;; Tag = 41 + LLVMDebugVersion 
      +             ;; (DW_TAG_file_type)
      +  metadata,  ;; Source file name
      +  metadata,  ;; Source file directory (includes trailing slash)
      +  metadata   ;; Reference to compile unit where defined
      +}
      +
      +
      + +

      These descriptors contain information for a file. Global variables and top + level functions would be defined using this context.k File descriptors also + provide context for source line correspondence.

      + +

      Each input file is encoded as a separate file descriptor in LLVM debugging + information output. Each file descriptor would be defined using a + compile unit.

      @@ -382,12 +396,12 @@ height="369"> metadata, ;; Name metadata, ;; Display name (fully qualified C++ name) metadata, ;; MIPS linkage name (for C++) - metadata, ;; Reference to compile unit where defined + metadata, ;; Reference to file where defined i32, ;; Line number where defined metadata, ;; Reference to type descriptor i1, ;; True if the global is local to compile unit (static) i1, ;; True if the global is defined in the compile unit (not extern) - { }* ;; Reference to the global variable + {}* ;; Reference to the global variable } @@ -414,11 +428,18 @@ provide details such as name, type and where the variable is defined.

      metadata, ;; Name metadata, ;; Display name (fully qualified C++ name) metadata, ;; MIPS linkage name (for C++) - metadata, ;; Reference to compile unit where defined + metadata, ;; Reference to file where defined i32, ;; Line number where defined metadata, ;; Reference to type descriptor i1, ;; True if the global is local to compile unit (static) i1 ;; True if the global is defined in the compile unit (not extern) + i32 ;; Virtuality, e.g. dwarf::DW_VIRTUALITY__virtual + i32 ;; Index into a virtual function + metadata, ;; indicates which base type contains the vtable pointer for the + ;; derived class + i1 ;; isArtificial + i1 ;; isOptimized + Function *;; Pointer to LLVM function } @@ -439,15 +460,19 @@ provide details such as name, type and where the variable is defined.

       !3 = metadata !{
      -  i32,     ;; Tag = 13 + LLVMDebugVersion (DW_TAG_lexical_block)
      -  metadata ;; Reference to context descriptor
      +  i32,     ;; Tag = 11 + LLVMDebugVersion (DW_TAG_lexical_block)
      +  metadata,;; Reference to context descriptor
      +  i32,     ;; Line number
      +  i32,     ;; Column number
      +  metadata,;; Reference to source file
      +  i32      ;; Unique ID to identify blocks from a template function
       }
       

      These descriptors provide debug information about nested blocks within a - subprogram. The array of member descriptors is used to define local - variables and deeper nested blocks.

      + subprogram. The line number and column numbers are used to dinstinguish + two lexical blocks at same depth.

      @@ -465,7 +490,7 @@ provide details such as name, type and where the variable is defined.

      ;; (DW_TAG_base_type) metadata, ;; Reference to context (typically a compile unit) metadata, ;; Name (may be "" for anonymous types) - metadata, ;; Reference to compile unit where defined (may be NULL) + metadata, ;; Reference to file where defined (may be NULL) i32, ;; Line number where defined (may be 0) i64, ;; Size in bits i64, ;; Alignment in bits @@ -516,11 +541,11 @@ DW_ATE_unsigned_char = 8 i32, ;; Tag (see below) metadata, ;; Reference to context metadata, ;; Name (may be "" for anonymous types) - metadata, ;; Reference to compile unit where defined (may be NULL) + metadata, ;; Reference to file where defined (may be NULL) i32, ;; Line number where defined (may be 0) - i32, ;; Size in bits - i32, ;; Alignment in bits - i32, ;; Offset in bits + i64, ;; Size in bits + i64, ;; Alignment in bits + i64, ;; Offset in bits metadata ;; Reference to type derived from } @@ -565,9 +590,8 @@ DW_TAG_restrict_type = 55 the bit offset if embedded in a composite type.

      -

      Note that the void * type is expressed as a - llvm.dbg.derivedtype.type with tag of DW_TAG_pointer_type - and NULL derived type.

      +

      Note that the void * type is expressed as a type derived from NULL. +

      @@ -584,7 +608,7 @@ DW_TAG_restrict_type = 55 i32, ;; Tag (see below) metadata, ;; Reference to context metadata, ;; Name (may be "" for anonymous types) - metadata, ;; Reference to compile unit where defined (may be NULL) + metadata, ;; Reference to file where defined (may be NULL) i32, ;; Line number where defined (may be 0) i64, ;; Size in bits i64, ;; Alignment in bits @@ -666,7 +690,7 @@ DW_TAG_inheritance = 28
      -%llvm.dbg.subrange.type = type {
      +!42 = metadata !{
         i32,    ;; Tag = 33 + LLVMDebugVersion (DW_TAG_subrange_type)
         i64,    ;; Low value
         i64     ;; High value
      @@ -719,8 +743,9 @@ DW_TAG_inheritance      = 28
         i32,      ;; Tag (see below)
         metadata, ;; Context
         metadata, ;; Name
      -  metadata, ;; Reference to compile unit where defined
      -  i32,      ;; Line number where defined
      +  metadata, ;; Reference to file where defined
      +  i32,      ;; 24 bit - Line number where defined
      +            ;; 8 bit - Argument number. 1 indicates 1st argument.
         metadata  ;; Type descriptor
       }
       
      @@ -763,272 +788,196 @@ DW_TAG_return_variable = 258
      -  void %llvm.dbg.stoppoint( uint, uint, metadata)
      +  void %llvm.dbg.declare(metadata, metadata)
       
      -

      This intrinsic is used to provide correspondence between the source file and - the generated code. The first argument is the line number (base 1), second - argument is the column number (0 if unknown) and the third argument the - source %llvm.dbg.compile_unit. - Code following a call to this intrinsic will - have been defined in close proximity of the line, column and file. This - information holds until the next call - to %lvm.dbg.stoppoint.

      - +

      This intrinsic provides information about a local element (ex. variable.) The + first argument is metadata holding alloca for the variable.. The + second argument is metadata containing description of the variable.

      -  void %llvm.dbg.func.start( metadata )
      +  void %llvm.dbg.value(metadata, i64, metadata)
       
      -

      This intrinsic is used to link the debug information - in %llvm.dbg.subprogram to the - function. It defines the beginning of the function's declarative region - (scope). It also implies a call to - %llvm.dbg.stoppoint which - defines a source line "stop point". The intrinsic should be called early in - the function after the all the alloca instructions. It should be paired off - with a closing - %llvm.dbg.region.end. - The function's single argument is - the %llvm.dbg.subprogram.type.

      - +

      This intrinsic provides information when a user source variable is set to a + new value. The first argument is the new value (wrapped as metadata). The + second argument is the offset in the user source variable where the new value + is written. The third argument is metadata containing description of the + user source variable.

      -
      - llvm.dbg.region.start +
      -
      -  void %llvm.dbg.region.start( metadata )
      -
      - -

      This intrinsic is used to define the beginning of a declarative scope (ex. - block) for local language elements. It should be paired off with a closing - %llvm.dbg.region.end. The - function's single argument is - the %llvm.dbg.block which is - starting.

      +

      In many languages, the local variables in functions can have their lifetimes + or scopes limited to a subset of a function. In the C family of languages, + for example, variables are only live (readable and writable) within the + source block that they are defined in. In functional languages, values are + only readable after they have been defined. Though this is a very obvious + concept, it is non-trivial to model in LLVM, because it has no notion of + scoping in this sense, and does not want to be tied to a language's scoping + rules.

      +

      In order to handle this, the LLVM debug format uses the metadata attached to + llvm instructions to encode line number and scoping information. Consider + the following C fragment, for example:

      +
      +
      +1.  void foo() {
      +2.    int X = 21;
      +3.    int Y = 22;
      +4.    {
      +5.      int Z = 23;
      +6.      Z = X;
      +7.    }
      +8.    X = Y;
      +9.  }
      +
      - - +

      Compiled to LLVM, this function would be represented like this:

      -
      +
      -  void %llvm.dbg.region.end( metadata )
      -
      - -

      This intrinsic is used to define the end of a declarative scope (ex. block) - for local language elements. It should be paired off with an - opening %llvm.dbg.region.start - or %llvm.dbg.func.start. - The function's single argument is either - the %llvm.dbg.block or - the %llvm.dbg.subprogram.type - which is ending.

      +define void @foo() nounwind ssp { +entry: + %X = alloca i32, align 4 ; <i32*> [#uses=4] + %Y = alloca i32, align 4 ; <i32*> [#uses=4] + %Z = alloca i32, align 4 ; <i32*> [#uses=3] + %0 = bitcast i32* %X to {}* ; <{}*> [#uses=1] + call void @llvm.dbg.declare(metadata !{i32 * %X}, metadata !0), !dbg !7 + store i32 21, i32* %X, !dbg !8 + %1 = bitcast i32* %Y to {}* ; <{}*> [#uses=1] + call void @llvm.dbg.declare(metadata !{i32 * %Y}, metadata !9), !dbg !10 + store i32 22, i32* %Y, !dbg !11 + %2 = bitcast i32* %Z to {}* ; <{}*> [#uses=1] + call void @llvm.dbg.declare(metadata !{i32 * %Z}, metadata !12), !dbg !14 + store i32 23, i32* %Z, !dbg !15 + %tmp = load i32* %X, !dbg !16 ; <i32> [#uses=1] + %tmp1 = load i32* %Y, !dbg !16 ; <i32> [#uses=1] + %add = add nsw i32 %tmp, %tmp1, !dbg !16 ; <i32> [#uses=1] + store i32 %add, i32* %Z, !dbg !16 + %tmp2 = load i32* %Y, !dbg !17 ; <i32> [#uses=1] + store i32 %tmp2, i32* %X, !dbg !17 + ret void, !dbg !18 +} +declare void @llvm.dbg.declare(metadata, metadata) nounwind readnone + +!0 = metadata !{i32 459008, metadata !1, metadata !"X", + metadata !3, i32 2, metadata !6}; [ DW_TAG_auto_variable ] +!1 = metadata !{i32 458763, metadata !2}; [DW_TAG_lexical_block ] +!2 = metadata !{i32 458798, i32 0, metadata !3, metadata !"foo", metadata !"foo", + metadata !"foo", metadata !3, i32 1, metadata !4, + i1 false, i1 true}; [DW_TAG_subprogram ] +!3 = metadata !{i32 458769, i32 0, i32 12, metadata !"foo.c", + metadata !"/private/tmp", metadata !"clang 1.1", i1 true, + i1 false, metadata !"", i32 0}; [DW_TAG_compile_unit ] +!4 = metadata !{i32 458773, metadata !3, metadata !"", null, i32 0, i64 0, i64 0, + i64 0, i32 0, null, metadata !5, i32 0}; [DW_TAG_subroutine_type ] +!5 = metadata !{null} +!6 = metadata !{i32 458788, metadata !3, metadata !"int", metadata !3, i32 0, + i64 32, i64 32, i64 0, i32 0, i32 5}; [DW_TAG_base_type ] +!7 = metadata !{i32 2, i32 7, metadata !1, null} +!8 = metadata !{i32 2, i32 3, metadata !1, null} +!9 = metadata !{i32 459008, metadata !1, metadata !"Y", metadata !3, i32 3, + metadata !6}; [ DW_TAG_auto_variable ] +!10 = metadata !{i32 3, i32 7, metadata !1, null} +!11 = metadata !{i32 3, i32 3, metadata !1, null} +!12 = metadata !{i32 459008, metadata !13, metadata !"Z", metadata !3, i32 5, + metadata !6}; [ DW_TAG_auto_variable ] +!13 = metadata !{i32 458763, metadata !1}; [DW_TAG_lexical_block ] +!14 = metadata !{i32 5, i32 9, metadata !13, null} +!15 = metadata !{i32 5, i32 5, metadata !13, null} +!16 = metadata !{i32 6, i32 5, metadata !13, null} +!17 = metadata !{i32 8, i32 3, metadata !1, null} +!18 = metadata !{i32 9, i32 1, metadata !2, null} +
      - - +

      This example illustrates a few important details about LLVM debugging + information. In particular, it shows how the llvm.dbg.declare + intrinsic and location information, which are attached to an instruction, + are applied together to allow a debugger to analyze the relationship between + statements, variable definitions, and the code used to implement the + function.

      -
      +
      -  void %llvm.dbg.declare( { } *, metadata )
      +call void @llvm.dbg.declare(metadata, metadata !0), !dbg !7   
       
      - -

      This intrinsic provides information about a local element (ex. variable.) The - first argument is the alloca for the variable, cast to a { }*. The - second argument is - the %llvm.dbg.variable containing - the description of the variable.

      -
      - - - -
      - -

      LLVM debugger "stop points" are a key part of the debugging representation - that allows the LLVM to maintain simple semantics - for debugging optimized code. The basic idea is that - the front-end inserts calls to - the %llvm.dbg.stoppoint - intrinsic function at every point in the program where a debugger should be - able to inspect the program (these correspond to places a debugger stops when - you "step" through it). The front-end can choose to place these as - fine-grained as it would like (for example, before every subexpression - evaluated), but it is recommended to only put them after every source - statement that includes executable code.

      - -

      Using calls to this intrinsic function to demark legal points for the - debugger to inspect the program automatically disables any optimizations that - could potentially confuse debugging information. To - non-debug-information-aware transformations, these calls simply look like - calls to an external function, which they must assume to do anything - (including reading or writing to any part of reachable memory). On the other - hand, it does not impact many optimizations, such as code motion of - non-trapping instructions, nor does it impact optimization of subexpressions, - code duplication transformations, or basic-block reordering - transformations.

      +

      The first intrinsic + %llvm.dbg.declare + encodes debugging information for the variable X. The metadata + !dbg !7 attached to the intrinsic provides scope information for the + variable X.

      +
      +
      +!7 = metadata !{i32 2, i32 7, metadata !1, null}
      +!1 = metadata !{i32 458763, metadata !2}; [DW_TAG_lexical_block ]
      +!2 = metadata !{i32 458798, i32 0, metadata !3, metadata !"foo", 
      +                metadata !"foo", metadata !"foo", metadata !3, i32 1, 
      +                metadata !4, i1 false, i1 true}; [DW_TAG_subprogram ]   
      +
      - - - -
      -

      In many languages, the local variables in functions can have their lifetime - or scope limited to a subset of a function. In the C family of languages, - for example, variables are only live (readable and writable) within the - source block that they are defined in. In functional languages, values are - only readable after they have been defined. Though this is a very obvious - concept, it is also non-trivial to model in LLVM, because it has no notion of - scoping in this sense, and does not want to be tied to a language's scoping - rules.

      +

      Here !7 is metadata providing location information. It has four + fields: line number, column number, scope, and original scope. The original + scope represents inline location if this instruction is inlined inside a + caller, and is null otherwise. In this example, scope is encoded by + !1. !1 represents a lexical block inside the scope + !2, where !2 is a + subprogram descriptor. This way the + location information attached to the intrinsics indicates that the + variable X is declared at line number 2 at a function level scope in + function foo.

      -

      In order to handle this, the LLVM debug format uses the notion of "regions" - of a function, delineated by calls to intrinsic functions. These intrinsic - functions define new regions of the program and indicate when the region - lifetime expires. Consider the following C fragment, for example:

      +

      Now lets take another example.

      -1.  void foo() {
      -2.    int X = ...;
      -3.    int Y = ...;
      -4.    {
      -5.      int Z = ...;
      -6.      ...
      -7.    }
      -8.    ...
      -9.  }
      +call void @llvm.dbg.declare(metadata, metadata !12), !dbg !14
       
      -

      Compiled to LLVM, this function would be represented like this:

      +

      The second intrinsic + %llvm.dbg.declare + encodes debugging information for variable Z. The metadata + !dbg !14 attached to the intrinsic provides scope information for + the variable Z.

      -void %foo() {
      -entry:
      -    %X = alloca int
      -    %Y = alloca int
      -    %Z = alloca int
      -    
      -    ...
      -    
      -    call void @llvm.dbg.func.start( metadata !0)
      -    
      -    call void @llvm.dbg.stoppoint( uint 2, uint 2, metadata !1)
      -    
      -    call void @llvm.dbg.declare({}* %X, ...)
      -    call void @llvm.dbg.declare({}* %Y, ...)
      -    
      -    ;; Evaluate expression on line 2, assigning to X.
      -    
      -    call void @llvm.dbg.stoppoint( uint 3, uint 2, metadata !1)
      -    
      -    ;; Evaluate expression on line 3, assigning to Y.
      -    
      -    call void @llvm.region.start()
      -    call void @llvm.dbg.stoppoint( uint 5, uint 4, metadata !1)
      -    call void @llvm.dbg.declare({}* %X, ...)
      -    
      -    ;; Evaluate expression on line 5, assigning to Z.
      -    
      -    call void @llvm.dbg.stoppoint( uint 7, uint 2, metadata !1)
      -    call void @llvm.region.end()
      -    
      -    call void @llvm.dbg.stoppoint( uint 9, uint 2, metadata !1)
      -    
      -    call void @llvm.region.end()
      -    
      -    ret void
      -}
      +!13 = metadata !{i32 458763, metadata !1}; [DW_TAG_lexical_block ]
      +!14 = metadata !{i32 5, i32 9, metadata !13, null}
       
      -

      This example illustrates a few important details about the LLVM debugging - information. In particular, it shows how the various intrinsics are applied - together to allow a debugger to analyze the relationship between statements, - variable definitions, and the code used to implement the function.

      - -

      The first - intrinsic %llvm.dbg.func.start - provides a link with the subprogram - descriptor containing the details of this function. This call also - defines the beginning of the function region, bounded by - the %llvm.region.end at the - end of the function. This region is used to bracket the lifetime of - variables declared within. For a function, this outer region defines a new - stack frame whose lifetime ends when the region is ended.

      - -

      It is possible to define inner regions for short term variables by using the - %llvm.region.start - and %llvm.region.end to - bound a region. The inner region in this example would be for the block - containing the declaration of Z.

      - -

      Using regions to represent the boundaries of source-level functions allow - LLVM interprocedural optimizations to arbitrarily modify LLVM functions - without having to worry about breaking mapping information between the LLVM - code and the and source-level program. In particular, the inliner requires - no modification to support inlining with debugging information: there is no - explicit correlation drawn between LLVM functions and their source-level - counterparts (note however, that if the inliner inlines all instances of a - non-strong-linkage function into its caller that it will not be possible for - the user to manually invoke the inlined function from a debugger).

      - -

      Once the function has been defined, - the stopping point - corresponding to line #2 (column #2) of the function is encountered. At this - point in the function, no local variables are live. As lines 2 and 3 - of the example are executed, their variable definitions are introduced into - the program using - %llvm.dbg.declare, without the - need to specify a new region. These variables do not require new regions to - be introduced because they go out of scope at the same point in the program: - line 9.

      - -

      In contrast, the Z variable goes out of scope at a different time, - on line 7. For this reason, it is defined within the inner region, which - kills the availability of Z before the code for line 8 is executed. - In this way, regions can support arbitrary source-language scoping rules, as - long as they can only be nested (ie, one scope cannot partially overlap with - a part of another scope).

      - -

      It is worth noting that this scoping mechanism is used to control scoping of - all declarations, not just variable declarations. For example, the scope of - a C++ using declaration is controlled with this and could change how name - lookup is performed.

      +

      Here !14 indicates that Z is declared at line number 5 and + column number 9 inside of lexical scope !13. The lexical scope + itself resides inside of lexical scope !1 described above.

      + +

      The scope information attached with each instruction provides a + straightforward way to find instructions covered by a scope.

      @@ -1087,10 +1036,10 @@ int main(int argc, char *argv[]) {
       ...
       ;;
      -;; Define the compile unit for the source file "/Users/mine/sources/MySource.cpp".
      +;; Define the compile unit for the main source file "/Users/mine/sources/MySource.cpp".
       ;;
      -!3 = metadata !{
      -  i32 458769,    ;; Tag
      +!2 = metadata !{
      +  i32 524305,    ;; Tag
         i32 0,         ;; Unused
         i32 4,         ;; Language Id
         metadata !"MySource.cpp", 
      @@ -1102,24 +1051,41 @@ int main(int argc, char *argv[]) {
         i32 0}         ;; Runtime version
       
       ;;
      -;; Define the compile unit for the header file "/Users/mine/sources/MyHeader.h".
      +;; Define the file for the file "/Users/mine/sources/MySource.cpp".
       ;;
       !1 = metadata !{
      -  i32 458769,    ;; Tag
      -  i32 0,         ;; Unused
      -  i32 4,         ;; Language Id
      -  metadata !"MyHeader.h", 
      +  i32 524329,    ;; Tag
      +  metadata !"MySource.cpp", 
         metadata !"/Users/mine/sources", 
      -  metadata !"4.2.1 (Based on Apple Inc. build 5649) (LLVM build 00)", 
      -  i1 false,      ;; Main Compile Unit
      -  i1 false,      ;; Optimized compile unit
      -  metadata !"",  ;; Compiler flags
      -  i32 0}         ;; Runtime version
      +  metadata !2    ;; Compile unit
      +}
      +
      +;;
      +;; Define the file for the file "/Users/mine/sources/Myheader.h"
      +;;
      +!3 = metadata !{
      +  i32 524329,    ;; Tag
      +  metadata !"Myheader.h"
      +  metadata !"/Users/mine/sources", 
      +  metadata !2    ;; Compile unit
      +}
       
       ...
       
      +

      llvm::Instruction provides easy access to metadata attached with an +instruction. One can extract line number information encoded in LLVM IR +using Instruction::getMetadata() and +DILocation::getLineNumber(). +

      + if (MDNode *N = I->getMetadata("dbg")) {  // Here I is an LLVM instruction
      +   DILocation Loc(N);                      // DILocation is in DebugInfo.h
      +   unsigned Line = Loc.getLineNumber();
      +   StringRef File = Loc.getFilename();
      +   StringRef Dir = Loc.getDirectory();
      + }
      +
      @@ -1156,15 +1122,15 @@ int MyGlobal = 100; ;; variable anchor and the global variable itself. ;; !0 = metadata !{ - i32 458804, ;; Tag + i32 524340, ;; Tag i32 0, ;; Unused metadata !1, ;; Context metadata !"MyGlobal", ;; Name metadata !"MyGlobal", ;; Display Name metadata !"MyGlobal", ;; Linkage Name - metadata !1, ;; Compile Unit + metadata !3, ;; Compile Unit i32 1, ;; Line Number - metadata !2, ;; Type + metadata !4, ;; Type i1 false, ;; Is a local variable i1 true, ;; Is this a definition i32* @MyGlobal ;; The global variable @@ -1174,11 +1140,11 @@ int MyGlobal = 100; ;; Define the basic type of 32 bit signed integer. Note that since int is an ;; intrinsic type the source file is NULL and line 0. ;; -!2 = metadata !{ - i32 458788, ;; Tag +!4 = metadata !{ + i32 524324, ;; Tag metadata !1, ;; Context metadata !"int", ;; Name - metadata !1, ;; Compile Unit + metadata !1, ;; File i32 0, ;; Line number i64 32, ;; Size in Bits i64 32, ;; Align in Bits @@ -1218,16 +1184,16 @@ int main(int argc, char *argv[]) { ;; anchor is 46, which is the same as the tag for subprograms ;; (46 = DW_TAG_subprogram.) ;; -!0 = metadata !{ - i32 458798, ;; Tag +!6 = metadata !{ + i32 524334, ;; Tag i32 0, ;; Unused metadata !1, ;; Context metadata !"main", ;; Name metadata !"main", ;; Display name metadata !"main", ;; Linkage name - metadata !1, ;; Compile unit + metadata !1, ;; File i32 1, ;; Line number - metadata !2, ;; Type + metadata !4, ;; Type i1 false, ;; Is local i1 true ;; Is definition } @@ -1263,10 +1229,10 @@ define i32 @main(i32 %argc, i8** %argv) {
       !2 = metadata !{
      -  i32 458788,        ;; Tag
      +  i32 524324,        ;; Tag
         metadata !1,       ;; Context
         metadata !"bool",  ;; Name
      -  metadata !1,       ;; Compile Unit
      +  metadata !1,       ;; File
         i32 0,             ;; Line number
         i64 8,             ;; Size in Bits
         i64 8,             ;; Align in Bits
      @@ -1289,10 +1255,10 @@ define i32 @main(i32 %argc, i8** %argv) {
       
       !2 = metadata !{
      -  i32 458788,        ;; Tag
      +  i32 524324,        ;; Tag
         metadata !1,       ;; Context
         metadata !"char",  ;; Name
      -  metadata !1,       ;; Compile Unit
      +  metadata !1,       ;; File
         i32 0,             ;; Line number
         i64 8,             ;; Size in Bits
         i64 8,             ;; Align in Bits
      @@ -1315,10 +1281,10 @@ define i32 @main(i32 %argc, i8** %argv) {
       
       !2 = metadata !{
      -  i32 458788,        ;; Tag
      +  i32 524324,        ;; Tag
         metadata !1,       ;; Context
         metadata !"unsigned char", 
      -  metadata !1,       ;; Compile Unit
      +  metadata !1,       ;; File
         i32 0,             ;; Line number
         i64 8,             ;; Size in Bits
         i64 8,             ;; Align in Bits
      @@ -1341,10 +1307,10 @@ define i32 @main(i32 %argc, i8** %argv) {
       
       !2 = metadata !{
      -  i32 458788,        ;; Tag
      +  i32 524324,        ;; Tag
         metadata !1,       ;; Context
         metadata !"short int",
      -  metadata !1,       ;; Compile Unit
      +  metadata !1,       ;; File
         i32 0,             ;; Line number
         i64 16,            ;; Size in Bits
         i64 16,            ;; Align in Bits
      @@ -1367,10 +1333,10 @@ define i32 @main(i32 %argc, i8** %argv) {
       
       !2 = metadata !{
      -  i32 458788,        ;; Tag
      +  i32 524324,        ;; Tag
         metadata !1,       ;; Context
         metadata !"short unsigned int",
      -  metadata !1,       ;; Compile Unit
      +  metadata !1,       ;; File
         i32 0,             ;; Line number
         i64 16,            ;; Size in Bits
         i64 16,            ;; Align in Bits
      @@ -1393,10 +1359,10 @@ define i32 @main(i32 %argc, i8** %argv) {
       
       !2 = metadata !{
      -  i32 458788,        ;; Tag
      +  i32 524324,        ;; Tag
         metadata !1,       ;; Context
         metadata !"int",   ;; Name
      -  metadata !1,       ;; Compile Unit
      +  metadata !1,       ;; File
         i32 0,             ;; Line number
         i64 32,            ;; Size in Bits
         i64 32,            ;; Align in Bits
      @@ -1418,10 +1384,10 @@ define i32 @main(i32 %argc, i8** %argv) {
       
       !2 = metadata !{
      -  i32 458788,        ;; Tag
      +  i32 524324,        ;; Tag
         metadata !1,       ;; Context
         metadata !"unsigned int",
      -  metadata !1,       ;; Compile Unit
      +  metadata !1,       ;; File
         i32 0,             ;; Line number
         i64 32,            ;; Size in Bits
         i64 32,            ;; Align in Bits
      @@ -1444,10 +1410,10 @@ define i32 @main(i32 %argc, i8** %argv) {
       
       !2 = metadata !{
      -  i32 458788,        ;; Tag
      +  i32 524324,        ;; Tag
         metadata !1,       ;; Context
         metadata !"long long int",
      -  metadata !1,       ;; Compile Unit
      +  metadata !1,       ;; File
         i32 0,             ;; Line number
         i64 64,            ;; Size in Bits
         i64 64,            ;; Align in Bits
      @@ -1470,10 +1436,10 @@ define i32 @main(i32 %argc, i8** %argv) {
       
       !2 = metadata !{
      -  i32 458788,        ;; Tag
      +  i32 524324,        ;; Tag
         metadata !1,       ;; Context
         metadata !"long long unsigned int",
      -  metadata !1,       ;; Compile Unit
      +  metadata !1,       ;; File
         i32 0,             ;; Line number
         i64 64,            ;; Size in Bits
         i64 64,            ;; Align in Bits
      @@ -1496,10 +1462,10 @@ define i32 @main(i32 %argc, i8** %argv) {
       
       !2 = metadata !{
      -  i32 458788,        ;; Tag
      +  i32 524324,        ;; Tag
         metadata !1,       ;; Context
         metadata !"float",
      -  metadata !1,       ;; Compile Unit
      +  metadata !1,       ;; File
         i32 0,             ;; Line number
         i64 32,            ;; Size in Bits
         i64 32,            ;; Align in Bits
      @@ -1522,10 +1488,10 @@ define i32 @main(i32 %argc, i8** %argv) {
       
       !2 = metadata !{
      -  i32 458788,        ;; Tag
      +  i32 524324,        ;; Tag
         metadata !1,       ;; Context
         metadata !"double",;; Name
      -  metadata !1,       ;; Compile Unit
      +  metadata !1,       ;; File
         i32 0,             ;; Line number
         i64 64,            ;; Size in Bits
         i64 64,            ;; Align in Bits
      @@ -1561,10 +1527,10 @@ typedef const int *IntPtr;
       ;; Define the typedef "IntPtr".
       ;;
       !2 = metadata !{
      -  i32 458774,          ;; Tag
      +  i32 524310,          ;; Tag
         metadata !1,         ;; Context
         metadata !"IntPtr",  ;; Name
      -  metadata !3,         ;; Compile unit
      +  metadata !3,         ;; File
         i32 0,               ;; Line number
         i64 0,               ;; Size in bits
         i64 0,               ;; Align in bits
      @@ -1577,10 +1543,10 @@ typedef const int *IntPtr;
       ;; Define the pointer type.
       ;;
       !4 = metadata !{
      -  i32 458767,          ;; Tag
      +  i32 524303,          ;; Tag
         metadata !1,         ;; Context
         metadata !"",        ;; Name
      -  metadata !1,         ;; Compile unit
      +  metadata !1,         ;; File
         i32 0,               ;; Line number
         i64 64,              ;; Size in bits
         i64 64,              ;; Align in bits
      @@ -1592,10 +1558,10 @@ typedef const int *IntPtr;
       ;; Define the const type.
       ;;
       !5 = metadata !{
      -  i32 458790,          ;; Tag
      +  i32 524326,          ;; Tag
         metadata !1,         ;; Context
         metadata !"",        ;; Name
      -  metadata !1,         ;; Compile unit
      +  metadata !1,         ;; File
         i32 0,               ;; Line number
         i64 32,              ;; Size in bits
         i64 32,              ;; Align in bits
      @@ -1607,10 +1573,10 @@ typedef const int *IntPtr;
       ;; Define the int type.
       ;;
       !6 = metadata !{
      -  i32 458788,          ;; Tag
      +  i32 524324,          ;; Tag
         metadata !1,         ;; Context
         metadata !"int",     ;; Name
      -  metadata !1,         ;; Compile unit
      +  metadata !1,         ;; File
         i32 0,               ;; Line number
         i64 32,              ;; Size in bits
         i64 32,              ;; Align in bits
      @@ -1650,10 +1616,10 @@ struct Color {
       ;; Define basic type for unsigned int.
       ;;
       !5 = metadata !{
      -  i32 458788,        ;; Tag
      +  i32 524324,        ;; Tag
         metadata !1,       ;; Context
         metadata !"unsigned int",
      -  metadata !1,       ;; Compile Unit
      +  metadata !1,       ;; File
         i32 0,             ;; Line number
         i64 32,            ;; Size in Bits
         i64 32,            ;; Align in Bits
      @@ -1665,7 +1631,7 @@ struct Color {
       ;; Define composite type for struct Color.
       ;;
       !2 = metadata !{
      -  i32 458771,        ;; Tag
      +  i32 524307,        ;; Tag
         metadata !1,       ;; Context
         metadata !"Color", ;; Name
         metadata !1,       ;; Compile unit
      @@ -1683,10 +1649,10 @@ struct Color {
       ;; Define the Red field.
       ;;
       !4 = metadata !{
      -  i32 458765,        ;; Tag
      +  i32 524301,        ;; Tag
         metadata !1,       ;; Context
         metadata !"Red",   ;; Name
      -  metadata !1,       ;; Compile Unit
      +  metadata !1,       ;; File
         i32 2,             ;; Line number
         i64 32,            ;; Size in bits
         i64 32,            ;; Align in bits
      @@ -1699,10 +1665,10 @@ struct Color {
       ;; Define the Green field.
       ;;
       !6 = metadata !{
      -  i32 458765,        ;; Tag
      +  i32 524301,        ;; Tag
         metadata !1,       ;; Context
         metadata !"Green", ;; Name
      -  metadata !1,       ;; Compile Unit
      +  metadata !1,       ;; File
         i32 3,             ;; Line number
         i64 32,            ;; Size in bits
         i64 32,            ;; Align in bits
      @@ -1715,10 +1681,10 @@ struct Color {
       ;; Define the Blue field.
       ;;
       !7 = metadata !{
      -  i32 458765,        ;; Tag
      +  i32 524301,        ;; Tag
         metadata !1,       ;; Context
         metadata !"Blue",  ;; Name
      -  metadata !1,       ;; Compile Unit
      +  metadata !1,       ;; File
         i32 4,             ;; Line number
         i64 32,            ;; Size in bits
         i64 32,            ;; Align in bits
      @@ -1763,10 +1729,10 @@ enum Trees {
       ;; Define composite type for enum Trees
       ;;
       !2 = metadata !{
      -  i32 458756,        ;; Tag
      +  i32 524292,        ;; Tag
         metadata !1,       ;; Context
         metadata !"Trees", ;; Name
      -  metadata !1,       ;; Compile unit
      +  metadata !1,       ;; File
         i32 1,             ;; Line number
         i64 32,            ;; Size in bits
         i64 32,            ;; Align in bits
      @@ -1785,17 +1751,17 @@ enum Trees {
       ;;
       ;; Define Spruce enumerator.
       ;;
      -!4 = metadata !{i32 458792, metadata !"Spruce", i64 100}
      +!4 = metadata !{i32 524328, metadata !"Spruce", i64 100}
       
       ;;
       ;; Define Oak enumerator.
       ;;
      -!5 = metadata !{i32 458792, metadata !"Oak", i64 200}
      +!5 = metadata !{i32 524328, metadata !"Oak", i64 200}
       
       ;;
       ;; Define Maple enumerator.
       ;;
      -!6 = metadata !{i32 458792, metadata !"Maple", i64 300}
      +!6 = metadata !{i32 524328, metadata !"Maple", i64 300}