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When GVN removes a redundant load, it should not modify the debug location of the dominating load. 

In the case of a fully redundant load LI dominated by an equivalent load V, GVN
should always preserve the original debug location of V. Otherwise, we risk to
introduce an incorrect stepping.
If V has debug info, then clearly it should not be modified. If V has a null
debugloc, then it is still potentially incorrect to propagate LI's debugloc
because LI may not post-dominate V.

Differential Revision: https://reviews.llvm.org/D27468

llvm-svn: 288903
This commit is contained in:
Andrea Di Biagio 2016-12-07 12:31:36 +00:00
parent 8893bd95f0
commit ae5780104f
2 changed files with 56 additions and 1 deletions
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5
llvm/lib/Transforms/Scalar/GVN.cpp
View File

@ -1700,7 +1700,10 @@ bool GVN::processNonLocalLoad(LoadInst *LI) {
if (isa<PHINode>(V))
V->takeName(LI);
if (Instruction *I = dyn_cast<Instruction>(V))
if (LI->getDebugLoc())
// If instruction I has debug info, then we should not update it.
// Also, if I has a null DebugLoc, then it is still potentially incorrect
// to propagate LI's DebugLoc because LI may not post-dominate I.
if (LI->getDebugLoc() && ValuesPerBlock.size() != 1)
I->setDebugLoc(LI->getDebugLoc());
if (V->getType()->getScalarType()->isPointerTy())
MD->invalidateCachedPointerInfo(V);

52
llvm/test/Transforms/GVN/dbg-redundant-load.ll Normal file
View File

@ -0,0 +1,52 @@
; RUN: opt -gvn -S < %s | FileCheck %s
; Check that the redundant load from %if.then is removed.
; Also, check that the debug location associated to load %0 still refers to
; line 3 and not line 6.
target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
; CHECK: @test_redundant_load(
; CHECK-LABEL: entry:
; CHECK-NEXT: load i32, i32* %Y, align 4, !dbg ![[LOC:[0-9]+]]
; CHECK-LABEL: if.then:
; CHECK-NOT: load
; CHECK-LABEL: if.end:
; CHECK: ![[LOC]] = !DILocation(line: 3, scope: !{{.*}})
define i32 @test_redundant_load(i32 %X, i32* %Y) !dbg !6 {
entry:
%0 = load i32, i32* %Y, align 4, !dbg !8
%cmp = icmp sgt i32 %X, -1, !dbg !9
br i1 %cmp, label %if.then, label %if.end, !dbg !9
if.then: ; preds = %entry
%1 = load i32, i32* %Y, align 4, !dbg !10
%add = add nsw i32 %0, %1, !dbg !10
call void @foo(), !dbg !11
br label %if.end, !dbg !12
if.end: ; preds = %if.then, %entry
%Result.0 = phi i32 [ %add, %if.then ], [ %0, %entry ]
ret i32 %Result.0, !dbg !13
}
declare void @foo()
!llvm.dbg.cu = !{!0}
!llvm.module.flags = !{!3, !4, !5}
!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !1, isOptimized: false, runtimeVersion: 0, emissionKind: LineTablesOnly, enums: !2)
!1 = !DIFile(filename: "test.cpp", directory: "")
!2 = !{}
!3 = !{i32 2, !"Dwarf Version", i32 4}
!4 = !{i32 2, !"Debug Info Version", i32 3}
!5 = !{i32 1, !"PIC Level", i32 2}
!6 = distinct !DISubprogram(name: "test_redundant_load", scope: !1, file: !1, line: 2, type: !7, isLocal: false, isDefinition: true, scopeLine: 2, flags: DIFlagPrototyped, isOptimized: false, unit: !0, variables: !2)
!7 = !DISubroutineType(types: !2)
!8 = !DILocation(line: 3, scope: !6)
!9 = !DILocation(line: 5, scope: !6)
!10 = !DILocation(line: 6, scope: !6)
!11 = !DILocation(line: 7, scope: !6)
!12 = !DILocation(line: 8, scope: !6)
!13 = !DILocation(line: 10, scope: !6)