[DebugInfo@O2] Fix pr41175 Dead Store Elimination missing debug loc

[Orlando]

Summary

Bug: https://bugs.llvm.org/show_bug.cgi?id=41175

In the bug test case the DSE pass is shortening the range of memory that a memset is working on. A getelementptr is generated so that the new starting address can be passed to memset. This instruction was not given a DebugLoc.

To fix the bug I copy the DebugLoc from the memset instruction.
I've added a test that checks this.

[aprantl]

llvm/test/Transforms/DeadStoreElimination/memset-missing-debugloc.ll

6

is the !16 necessary? Hardcoded numbers are bound to break sooner or later.

7

CHECK-NEXT?

[Orlando]

I've made the suggested changes.

Please could someone commit this change for me? I do not have commit access.

Thanks,
Orlando

[jmorse]

(I'll commit)

llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp

static bool tryToShorten(Instruction *EarlierWrite, int64_t &EarlierOffset,
   EarlierSize = NewLength;
   if (!IsOverwriteEnd) {
     int64_t OffsetMoved = (LaterOffset - EarlierOffset);
     Value *Indices[1] = {
         ConstantInt::get(EarlierWriteLength->getType(), OffsetMoved)};
     GetElementPtrInst *NewDestGEP = GetElementPtrInst::CreateInBounds(
         EarlierIntrinsic->getRawDest()->getType()->getPointerElementType(),
         EarlierIntrinsic->getRawDest(), Indices, "", EarlierWrite);
+    NewDestGEP->setDebugLoc(EarlierIntrinsic->getDebugLoc());
     EarlierIntrinsic->setDest(NewDestGEP);
     EarlierOffset = EarlierOffset + OffsetMoved;
   }
   return true;
 }
 
 static bool tryToShortenEnd(Instruction *EarlierWrite,
                             OverlapIntervalsTy &IntervalMap,

llvm/test/Transforms/DeadStoreElimination/memset-missing-debugloc.ll

+; Test that the getelementptr generated when the dse pass determines that
+; a memset can be shortened has the debugloc carried over from the memset.
+
+; RUN: opt -S -march=native -dse < %s| FileCheck %s
+; CHECK: bitcast [5 x i64]* %{{[a-zA-Z_][a-zA-Z0-9_]*}} to i8*, !dbg
+; CHECK-NEXT: %{{[0-9]+}} = getelementptr inbounds i8, i8* %0, i64 32, !dbg ![[DBG:[0-9]+]]
+; CHECK: ![[DBG]] = !DILocation(line: 2,
+
+; The test IR is generated by running:
+;
+; clang Debugify_Dead_Store_Elimination.cpp -Wno-c++11-narrowing -S \
+;   -emit-llvm -O0 -w -Xclang -disable-O0-optnone -march=native -fdeclspec \
+;   --target=x86_64-gnu-linux-unknown -Werror=unreachable-code -o -
+;
+; Where Debugify_Dead_Store_Elimination.cpp contains:
+;
+; int a() {
+;   long b[]{2, 2, 2, 2, 0};
+;   if (a())
+;     ;
+; }
+
+
+define dso_local i32 @_Z1av() !dbg !7 {
+entry:
+  %retval = alloca i32, align 4
+  %b = alloca [5 x i64], align 16
+  call void @llvm.dbg.declare(metadata [5 x i64]* %b, metadata !11, metadata !DIExpression()), !dbg !16
+  %0 = bitcast [5 x i64]* %b to i8*, !dbg !16
+  call void @llvm.memset.p0i8.i64(i8* align 16 %0, i8 0, i64 40, i1 false), !dbg !16
+  %1 = bitcast i8* %0 to [5 x i64]*, !dbg !16
+  %2 = getelementptr inbounds [5 x i64], [5 x i64]* %1, i32 0, i32 0, !dbg !16
+  store i64 2, i64* %2, align 16, !dbg !16
+  %3 = getelementptr inbounds [5 x i64], [5 x i64]* %1, i32 0, i32 1, !dbg !16
+  store i64 2, i64* %3, align 8, !dbg !16
+  %4 = getelementptr inbounds [5 x i64], [5 x i64]* %1, i32 0, i32 2, !dbg !16
+  store i64 2, i64* %4, align 16, !dbg !16
+  %5 = getelementptr inbounds [5 x i64], [5 x i64]* %1, i32 0, i32 3, !dbg !16
+  store i64 2, i64* %5, align 8, !dbg !16
+  %call = call i32 @_Z1av(), !dbg !17
+  %tobool = icmp ne i32 %call, 0, !dbg !17
+  br i1 %tobool, label %if.then, label %if.end, !dbg !19
+
+if.then:                                          ; preds = %entry
+  br label %if.end, !dbg !19
+
+if.end:                                           ; preds = %if.then, %entry
+  call void @llvm.trap(), !dbg !20
+  unreachable, !dbg !20
+
+return:                                           ; No predecessors!
+  %6 = load i32, i32* %retval, align 4, !dbg !21
+  ret i32 %6, !dbg !21
+}
+
+; Function Attrs: nounwind readnone speculatable
+declare void @llvm.dbg.declare(metadata, metadata, metadata)
+
+; Function Attrs: argmemonly nounwind
+declare void @llvm.memset.p0i8.i64(i8* nocapture writeonly, i8, i64, i1 immarg)
+
+; Function Attrs: cold noreturn nounwind
+declare void @llvm.trap()
+
+!llvm.module.flags = !{!3, !4, !5}
+!llvm.ident = !{!6}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !1, producer: "clang version 9.0.0 (https://github.com/llvm/llvm-project.git eb1a156d7f7ba56ea8f9a26da36e6a93d1e98bda)", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, enums: !2, nameTableKind: None)
+!1 = !DIFile(filename: "Debugify_Dead_Store_Elimination.cpp", directory: "")
+!2 = !{}
+!3 = !{i32 2, !"Dwarf Version", i32 4}
+!4 = !{i32 2, !"Debug Info Version", i32 3}
+!5 = !{i32 1, !"wchar_size", i32 4}
+!6 = !{!"clang version 9.0.0 (https://github.com/llvm/llvm-project.git eb1a156d7f7ba56ea8f9a26da36e6a93d1e98bda)"}
+!7 = distinct !DISubprogram(name: "a", linkageName: "_Z1av", scope: !1, file: !1, line: 1, type: !8, scopeLine: 1, flags: DIFlagPrototyped, spFlags: DISPFlagDefinition, unit: !0, retainedNodes: !2)
+!8 = !DISubroutineType(types: !9)
+!9 = !{!10}
+!10 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!11 = !DILocalVariable(name: "b", scope: !7, file: !1, line: 2, type: !12)
+!12 = !DICompositeType(tag: DW_TAG_array_type, baseType: !13, size: 320, elements: !14)
+!13 = !DIBasicType(name: "long int", size: 64, encoding: DW_ATE_signed)
+!14 = !{!15}
+!15 = !DISubrange(count: 5)
+!16 = !DILocation(line: 2, column: 8, scope: !7)
+!17 = !DILocation(line: 3, column: 7, scope: !18)
+!18 = distinct !DILexicalBlock(scope: !7, file: !1, line: 3, column: 7)
+!19 = !DILocation(line: 3, column: 7, scope: !7)
+!20 = !DILocation(line: 3, column: 9, scope: !18)
+!21 = !DILocation(line: 5, column: 1, scope: !7)