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Do not propagate DebugLoc across basic blocks
Summary:
DebugLoc shouldn't be propagated across basic blocks to prevent incorrect stepping and imprecise sample profile result. rL288903 addressed the wrong DebugLoc propagation issue by limiting the copy of DebugLoc when GVN removes a fully redundant load that is dominated by some other load. However, DebugLoc is still incorrectly propagated in the following example:
```
1: extern int g;
2:
3: void foo(int x, int y, int z) {
4: if (x)
5: g = 0;
6: else
7: g = 1;
8:
9: int i = 0;
10: for ( ; i < y ; i++)
11: if (i > z)
12: g++;
13: }
```
Below is LLVM IR representation of the program before GVN:
```
@g = external local_unnamed_addr global i32, align 4
; Function Attrs: nounwind uwtable
define void @foo(i32 %x, i32 %y, i32 %z) local_unnamed_addr #0 !dbg !4 {
entry:
%not.tobool = icmp eq i32 %x, 0, !dbg !8
%.sink = zext i1 %not.tobool to i32, !dbg !8
store i32 %.sink, i32* @g, align 4, !tbaa !9
%cmp8 = icmp sgt i32 %y, 0, !dbg !13
br i1 %cmp8, label %for.body.preheader, label %for.end, !dbg !17
for.body.preheader: ; preds = %entry
br label %for.body, !dbg !19
for.body: ; preds = %for.body.preheader, %for.inc
%i.09 = phi i32 [ %inc4, %for.inc ], [ 0, %for.body.preheader ]
%cmp1 = icmp sgt i32 %i.09, %z, !dbg !19
br i1 %cmp1, label %if.then2, label %for.inc, !dbg !21
if.then2: ; preds = %for.body
%0 = load i32, i32* @g, align 4, !dbg !22, !tbaa !9
%inc = add nsw i32 %0, 1, !dbg !22
store i32 %inc, i32* @g, align 4, !dbg !22, !tbaa !9
br label %for.inc, !dbg !23
for.inc: ; preds = %for.body, %if.then2
%inc4 = add nuw nsw i32 %i.09, 1, !dbg !24
%exitcond = icmp ne i32 %inc4, %y, !dbg !13
br i1 %exitcond, label %for.body, label %for.end.loopexit, !dbg !17
for.end.loopexit: ; preds = %for.inc
br label %for.end, !dbg !26
for.end: ; preds = %for.end.loopexit, %entry
ret void, !dbg !26
}
```
where
```
!21 = !DILocation(line: 11, column: 9, scope: !15)
!22 = !DILocation(line: 12, column: 8, scope: !20)
!23 = !DILocation(line: 12, column: 7, scope: !20)
!24 = !DILocation(line: 10, column: 20, scope: !25)
```
And below is after GVN:
```
@g = external local_unnamed_addr global i32, align 4
define void @foo(i32 %x, i32 %y, i32 %z) local_unnamed_addr !dbg !4 {
entry:
%not.tobool = icmp eq i32 %x, 0, !dbg !8
%.sink = zext i1 %not.tobool to i32, !dbg !8
store i32 %.sink, i32* @g, align 4, !tbaa !9
%cmp8 = icmp sgt i32 %y, 0, !dbg !13
br i1 %cmp8, label %for.body.preheader, label %for.end, !dbg !17
for.body.preheader: ; preds = %entry
br label %for.body, !dbg !19
for.body: ; preds = %for.inc, %for.body.preheader
%0 = phi i32 [ %1, %for.inc ], [ %.sink, %for.body.preheader ], !dbg !21
%i.09 = phi i32 [ %inc4, %for.inc ], [ 0, %for.body.preheader ]
%cmp1 = icmp sgt i32 %i.09, %z, !dbg !19
br i1 %cmp1, label %if.then2, label %for.inc, !dbg !22
if.then2: ; preds = %for.body
%inc = add nsw i32 %0, 1, !dbg !21
store i32 %inc, i32* @g, align 4, !dbg !21, !tbaa !9
br label %for.inc, !dbg !23
for.inc: ; preds = %if.then2, %for.body
%1 = phi i32 [ %inc, %if.then2 ], [ %0, %for.body ]
%inc4 = add nuw nsw i32 %i.09, 1, !dbg !24
%exitcond = icmp ne i32 %inc4, %y, !dbg !13
br i1 %exitcond, label %for.body, label %for.end.loopexit, !dbg !17
for.end.loopexit: ; preds = %for.inc
br label %for.end, !dbg !26
for.end: ; preds = %for.end.loopexit, %entry
ret void, !dbg !26
}
```
As you see, GVN removes the load in if.then2 block and creates a phi instruction in for.body for it. The problem is that DebugLoc of remove load instruction is propagated to the newly created phi instruction, which is wrong. rL288903 cannot handle this case because ValuesPerBlock.size() is not 1 in this example when the load is removed.
Reviewers: aprantl, andreadb, wolfgangp
Reviewed By: andreadb
Subscribers: davide, llvm-commits
Differential Revision: https://reviews.llvm.org/D29254
llvm-svn: 293688
This commit is contained in:
Taewook Oh
parent
24741d447a
commit
46d149fe2d
@ -1714,7 +1714,7 @@ bool GVN::processNonLocalLoad(LoadInst *LI) {
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// If instruction I has debug info, then we should not update it.
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// Also, if I has a null DebugLoc, then it is still potentially incorrect
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// to propagate LI's DebugLoc because LI may not post-dominate I.
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if (LI->getDebugLoc() && ValuesPerBlock.size() != 1)
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if (LI->getDebugLoc() && LI->getParent() == I->getParent())
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I->setDebugLoc(LI->getDebugLoc());
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if (V->getType()->getScalarType()->isPointerTy())
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MD->invalidateCachedPointerInfo(V);
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@ -1796,7 +1796,7 @@ static void patchReplacementInstruction(Instruction *I, Value *Repl) {
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// Patch the replacement so that it is not more restrictive than the value
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// being replaced.
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// Note that if 'I' is a load being replaced by some operation,
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// Note that if 'I' is a load being replaced by some operation,
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// for example, by an arithmetic operation, then andIRFlags()
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// would just erase all math flags from the original arithmetic
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// operation, which is clearly not wanted and not needed.
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77
test/Transforms/GVN/debugloc.ll
Normal file
77
test/Transforms/GVN/debugloc.ll
Normal file
@ -0,0 +1,77 @@
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; RUN: opt < %s -gvn -S | FileCheck %s
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; CHECK: {{^}}for.body:
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; CHECK-NEXT: [[VREG1:%[^ ]+]] = phi{{.*}}[[VREG2:%[^ ]+]],{{.*}}%.sink,
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; CHECK-NOT: !dbg
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; CHECK-SAME: {{$}}
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; CHECK: {{^}}for.inc:
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; CHECK-NEXT: [[VREG2]] = phi{{.*}}%inc,{{.*}}[[VREG1]]
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target triple = "x86_64-unknown-linux-gnu"
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@g = external local_unnamed_addr global i32, align 4
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; Function Attrs: nounwind uwtable
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define void @foo(i32 %x, i32 %y, i32 %z) local_unnamed_addr #0 !dbg !4 {
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entry:
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%not.tobool = icmp eq i32 %x, 0, !dbg !8
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%.sink = zext i1 %not.tobool to i32, !dbg !8
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store i32 %.sink, i32* @g, align 4, !tbaa !9
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%cmp8 = icmp sgt i32 %y, 0, !dbg !13
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br i1 %cmp8, label %for.body.preheader, label %for.end, !dbg !17
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for.body.preheader: ; preds = %entry
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br label %for.body, !dbg !19
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for.body: ; preds = %for.body.preheader, %for.inc
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%i.09 = phi i32 [ %inc4, %for.inc ], [ 0, %for.body.preheader ]
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%cmp1 = icmp sgt i32 %i.09, %z, !dbg !19
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br i1 %cmp1, label %if.then2, label %for.inc, !dbg !21
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if.then2: ; preds = %for.body
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%0 = load i32, i32* @g, align 4, !dbg !22, !tbaa !9
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%inc = add nsw i32 %0, 1, !dbg !22
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store i32 %inc, i32* @g, align 4, !dbg !22, !tbaa !9
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br label %for.inc, !dbg !23
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for.inc: ; preds = %for.body, %if.then2
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%inc4 = add nuw nsw i32 %i.09, 1, !dbg !24
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%exitcond = icmp ne i32 %inc4, %y, !dbg !13
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br i1 %exitcond, label %for.body, label %for.end.loopexit, !dbg !17
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for.end.loopexit: ; preds = %for.inc
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br label %for.end, !dbg !26
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for.end: ; preds = %for.end.loopexit, %entry
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ret void, !dbg !26
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}
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!0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1)
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!1 = !DIFile(filename: "foo.c", directory: "b/")
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!2 = !{i32 2, !"Dwarf Version", i32 4}
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!3 = !{i32 2, !"Debug Info Version", i32 3}
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!4 = distinct !DISubprogram(name: "foo", scope: !1, file: !1, line: 3, type: !5, isLocal: false, isDefinition: true, scopeLine: 3, flags: DIFlagPrototyped, isOptimized: true, unit: !0)
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!5 = !DISubroutineType(types: !6)
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!6 = !{null, !7, !7, !7}
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!7 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
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!8 = !DILocation(line: 4, column: 7, scope: !4)
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!9 = !{!10, !10, i64 0}
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!10 = !{!"int", !11, i64 0}
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!11 = !{!"omnipotent char", !12, i64 0}
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!12 = !{!"Simple C/C++ TBAA"}
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!13 = !DILocation(line: 10, column: 13, scope: !14)
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!14 = !DILexicalBlockFile(scope: !15, file: !1, discriminator: 1)
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!15 = distinct !DILexicalBlock(scope: !16, file: !1, line: 10, column: 3)
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!16 = distinct !DILexicalBlock(scope: !4, file: !1, line: 10, column: 3)
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!17 = !DILocation(line: 10, column: 3, scope: !18)
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!18 = !DILexicalBlockFile(scope: !16, file: !1, discriminator: 1)
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!19 = !DILocation(line: 11, column: 11, scope: !20)
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!20 = distinct !DILexicalBlock(scope: !15, file: !1, line: 11, column: 9)
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!21 = !DILocation(line: 11, column: 9, scope: !15)
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!22 = !DILocation(line: 12, column: 8, scope: !20)
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!23 = !DILocation(line: 12, column: 7, scope: !20)
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!24 = !DILocation(line: 10, column: 20, scope: !25)
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!25 = !DILexicalBlockFile(scope: !15, file: !1, discriminator: 2)
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!26 = !DILocation(line: 13, column: 1, scope: !4)
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!llvm.dbg.cu = !{!0}
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!llvm.module.flags = !{!2, !3}
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78
test/Transforms/NewGVN/debugloc.ll
Normal file
78
test/Transforms/NewGVN/debugloc.ll
Normal file
@ -0,0 +1,78 @@
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; XFAIL: *
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; RUN: opt < %s -newgvn -S | FileCheck %s
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; CHECK: {{^}}for.body:
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; CHECK-NEXT: [[VREG1:%[^ ]+]] = phi{{.*}}[[VREG2:%[^ ]+]],{{.*}}%.sink,
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; CHECK-NOT: !dbg
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; CHECK-SAME: {{$}}
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; CHECK: {{^}}for.inc:
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; CHECK-NEXT: [[VREG2]] = phi{{.*}}%inc,{{.*}}[[VREG1]]
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target triple = "x86_64-unknown-linux-gnu"
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@g = external local_unnamed_addr global i32, align 4
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; Function Attrs: nounwind uwtable
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define void @foo(i32 %x, i32 %y, i32 %z) local_unnamed_addr #0 !dbg !4 {
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entry:
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%not.tobool = icmp eq i32 %x, 0, !dbg !8
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%.sink = zext i1 %not.tobool to i32, !dbg !8
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store i32 %.sink, i32* @g, align 4, !tbaa !9
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%cmp8 = icmp sgt i32 %y, 0, !dbg !13
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br i1 %cmp8, label %for.body.preheader, label %for.end, !dbg !17
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for.body.preheader: ; preds = %entry
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br label %for.body, !dbg !19
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for.body: ; preds = %for.body.preheader, %for.inc
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%i.09 = phi i32 [ %inc4, %for.inc ], [ 0, %for.body.preheader ]
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%cmp1 = icmp sgt i32 %i.09, %z, !dbg !19
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br i1 %cmp1, label %if.then2, label %for.inc, !dbg !21
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if.then2: ; preds = %for.body
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%0 = load i32, i32* @g, align 4, !dbg !22, !tbaa !9
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%inc = add nsw i32 %0, 1, !dbg !22
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store i32 %inc, i32* @g, align 4, !dbg !22, !tbaa !9
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br label %for.inc, !dbg !23
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for.inc: ; preds = %for.body, %if.then2
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%inc4 = add nuw nsw i32 %i.09, 1, !dbg !24
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%exitcond = icmp ne i32 %inc4, %y, !dbg !13
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br i1 %exitcond, label %for.body, label %for.end.loopexit, !dbg !17
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for.end.loopexit: ; preds = %for.inc
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br label %for.end, !dbg !26
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for.end: ; preds = %for.end.loopexit, %entry
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ret void, !dbg !26
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}
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!0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1)
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!1 = !DIFile(filename: "foo.c", directory: "b/")
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!2 = !{i32 2, !"Dwarf Version", i32 4}
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!3 = !{i32 2, !"Debug Info Version", i32 3}
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!4 = distinct !DISubprogram(name: "foo", scope: !1, file: !1, line: 3, type: !5, isLocal: false, isDefinition: true, scopeLine: 3, flags: DIFlagPrototyped, isOptimized: true, unit: !0)
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!5 = !DISubroutineType(types: !6)
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!6 = !{null, !7, !7, !7}
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!7 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
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!8 = !DILocation(line: 4, column: 7, scope: !4)
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!9 = !{!10, !10, i64 0}
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!10 = !{!"int", !11, i64 0}
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!11 = !{!"omnipotent char", !12, i64 0}
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!12 = !{!"Simple C/C++ TBAA"}
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!13 = !DILocation(line: 10, column: 13, scope: !14)
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!14 = !DILexicalBlockFile(scope: !15, file: !1, discriminator: 1)
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!15 = distinct !DILexicalBlock(scope: !16, file: !1, line: 10, column: 3)
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!16 = distinct !DILexicalBlock(scope: !4, file: !1, line: 10, column: 3)
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!17 = !DILocation(line: 10, column: 3, scope: !18)
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!18 = !DILexicalBlockFile(scope: !16, file: !1, discriminator: 1)
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!19 = !DILocation(line: 11, column: 11, scope: !20)
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!20 = distinct !DILexicalBlock(scope: !15, file: !1, line: 11, column: 9)
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!21 = !DILocation(line: 11, column: 9, scope: !15)
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!22 = !DILocation(line: 12, column: 8, scope: !20)
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!23 = !DILocation(line: 12, column: 7, scope: !20)
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!24 = !DILocation(line: 10, column: 20, scope: !25)
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!25 = !DILexicalBlockFile(scope: !15, file: !1, discriminator: 2)
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!26 = !DILocation(line: 13, column: 1, scope: !4)
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!llvm.dbg.cu = !{!0}
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!llvm.module.flags = !{!2, !3}
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