[LLVMdev] How to get the variable mapping between the source and llvm bytecode

[Eli Friedman]

On Thu, May 13, 2010 at 1:47 PM, Kecheng <kecheng at cecs.pdx.edu> wrote:
> Hi,
>
> I want to know the variable mapping between the source and llvm bytecode. It
> seems that current llvm debugging information cannot provide this mapping
> directly.
>
> Here is my examples (llvm 2.7). In this exmaple, I want to know the mapping:
> tmp<--->%4. But current llvm's debugging information can only provide that
> the instruction "%4 = add nsw i32 %3, 2" is at line 3 in the C source. But
> since there're two "+" at line 3, I don't have a direct way to know which
> "+" is mapped to this "add". Is there any way I can derive the mapping based
> on current ddg infor? Thanks.

You want to map the "+" in the source to a specific "add" instruction?
 clang does provide column number info, though, which might help a
bit.  In general, though, debug info isn't rich enough to provide that
sort of mapping.  What are you trying to do?

-Eli

> **************
> C source
> **************
> int h (int j, int i) {
>     int tmp;
>     tmp = j+i+2;
>     return tmp;
> }
>
> **************
> .ll file
> **************
> ; ModuleID = 'simplecase.c'
> target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64"
> target triple = "x86_64-unknown-linux-gnu"
> define i32 @h(i32 %j, i32 %i) nounwind {
> entry:
>   %j_addr = alloca i32                            ; <i32*> [#uses=2]
>   %i_addr = alloca i32                            ; <i32*> [#uses=2]
>   %retval = alloca i32                            ; <i32*> [#uses=2]
>   %0 = alloca i32                                 ; <i32*> [#uses=2]
>   %tmp = alloca i32                               ; <i32*> [#uses=2]
>   %"alloca point" = bitcast i32 0 to i32          ; <i32> [#uses=0]
>   call void @llvm.dbg.declare(metadata !{i32* %j_addr}, metadata !0), !dbg !6
>   store i32 %j, i32* %j_addr
>   call void @llvm.dbg.declare(metadata !{i32* %i_addr}, metadata !7), !dbg !6
>   store i32 %i, i32* %i_addr
>   call void @llvm.dbg.declare(metadata !{i32* %tmp}, metadata !8), !dbg !10
>   %1 = load i32* %j_addr, align 4, !dbg !11       ; <i32> [#uses=1]
>   %2 = load i32* %i_addr, align 4, !dbg !11       ; <i32> [#uses=1]
>   %3 = add nsw i32 %1, %2, !dbg !11               ; <i32> [#uses=1]
>   %4 = add nsw i32 %3, 2, !dbg !11                ; <i32> [#uses=1]
>   store i32 %4, i32* %tmp, align 4, !dbg !11
>   %5 = load i32* %tmp, align 4, !dbg !12          ; <i32> [#uses=1]
>   store i32 %5, i32* %0, align 4, !dbg !12
>   %6 = load i32* %0, align 4, !dbg !12            ; <i32> [#uses=1]
>   store i32 %6, i32* %retval, align 4, !dbg !12
>   br label %return, !dbg !12
> return:                                           ; preds = %entry
>   %retval1 = load i32* %retval, !dbg !12          ; <i32> [#uses=1]
>   ret i32 %retval1, !dbg !12
> }
> declare void @llvm.dbg.declare(metadata, metadata) nounwind readnone
> !0 = metadata !{i32 459009, metadata !1, metadata !"j", metadata !2, i32 1, metadata !5} ; [ DW_TAG_arg_variable ]
> !1 = metadata !{i32 458798, i32 0, metadata !2, metadata !"h", metadata !"h", metadata !"h", metadata !2, i32 1, metadata !3, i1 false, i1 true, i32 0, i32 0, null, i1 false} ; [ DW_TAG_subprogram ]
> !2 = metadata !{i32 458769, i32 0, i32 1, metadata !"simplecase.c", metadata !"/home/kecheng/cases/v2.7/simplecase/", metadata !"4.2.1 (Based on Apple Inc. build 5658) (LLVM build)", i1 true, i1 false, metadata !"", i32 0} ; [ DW_TAG_compile_unit ]
> !3 = metadata !{i32 458773, metadata !2, metadata !"", metadata !2, i32 0, i64 0, i64 0, i64 0, i32 0, null, metadata !4, i32 0, null} ; [ DW_TAG_subroutine_type ]
> !4 = metadata !{metadata !5, metadata !5, metadata !5}
> !5 = metadata !{i32 458788, metadata !2, metadata !"int", metadata !2, i32 0, i64 32, i64 32, i64 0, i32 0, i32 5} ; [ DW_TAG_base_type ]
> !6 = metadata !{i32 1, i32 0, metadata !1, null}
> !7 = metadata !{i32 459009, metadata !1, metadata !"i", metadata !2, i32 1, metadata !5} ; [ DW_TAG_arg_variable ]
> !8 = metadata !{i32 459008, metadata !9, metadata !"tmp", metadata !2, i32 2, metadata !5} ; [ DW_TAG_auto_variable ]
> !9 = metadata !{i32 458763, metadata !1, i32 1, i32 0} ; [ DW_TAG_lexical_block ]
> !10 = metadata !{i32 1, i32 0, metadata !9, null}
> !11 = metadata !{i32 3, i32 0, metadata !9, null}
> !12 = metadata !{i32 4, i32 0, metadata !9, null}
>
> Best,
>
> Kecheng
> 2010-05-13
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