[DebugInfo] Fix line number attribution in mldst-motion

[Orlando]

Summary

Taking the example from the test included in this patch:

$ cat test.cpp -n

1	void fun(int *a, int cond) {
2	  if (cond)
3	    a[1] = 1;
4	  else
5	    a[1] = 2;
6	}

mldst-motion will merge and sink the stores in if.then and if.else into
if.end. The resultant PHI, gep and store should be attributed line zero
with the innermost common scope rather than picking a debug location from
one of the original stores.

[djtodoro]

lgtm, thanks

llvm/test/DebugInfo/Generic/mldst-motion-dbg.ll

26

Nit: could drop dso_local and local_unnamed_addr #0

74–77

No need for tbaa.

[Orlando]

Done, thanks!

llvm/lib/Transforms/Scalar/MergedLoadStoreMotion.cpp

void MergedLoadStoreMotion::sinkStoresAndGEPs(BasicBlock *BB, StoreInst *S0,
   LLVM_DEBUG(dbgs() << "Sink Instruction into BB \n"; BB->dump();
              dbgs() << "Instruction Left\n"; S0->dump(); dbgs() << "\n";
              dbgs() << "Instruction Right\n"; S1->dump(); dbgs() << "\n");
   // Hoist the instruction.
   BasicBlock::iterator InsertPt = BB->getFirstInsertionPt();
   // Intersect optional metadata.
   S0->andIRFlags(S1);
   S0->dropUnknownNonDebugMetadata();
+  S0->applyMergedLocation(S0->getDebugLoc(), S1->getDebugLoc());
 
   // Create the new store to be inserted at the join point.
   StoreInst *SNew = cast<StoreInst>(S0->clone());
   Instruction *ANew = A0->clone();
   SNew->insertBefore(&*InsertPt);
   ANew->insertBefore(SNew);
+  ANew->applyMergedLocation(A0->getDebugLoc(), A1->getDebugLoc());
 
   assert(S0->getParent() == A0->getParent());
   assert(S1->getParent() == A1->getParent());
 
   // New PHI operand? Use it.
   if (PHINode *NewPN = getPHIOperand(BB, S0, S1))
     SNew->setOperand(0, NewPN);
   S0->eraseFromParent();

llvm/test/DebugInfo/Generic/mldst-motion-dbg.ll

+; RUN: opt -passes=mldst-motion -S %s -o - | FileCheck %s
+
+;; $ cat test.cpp -n
+;;      1 void fun(int *a, int cond) {
+;;      2   if (cond)
+;;      3     a[1] = 1;
+;;      4   else
+;;      5     a[1] = 2;
+;;      6 }
+;;
+;; mldst-motion will merge and sink the stores in if.then and if.else into
+;; if.end. The resultant PHI, gep and store should be attributed line zero
+;; with the innermost common scope rather than picking a debug location from
+;; one of the original stores.
+
+; CHECK: if.end:
+; CHECK-NEXT: %.sink = phi i32 [ 2, %if.else ], [ 1, %if.then ], !dbg ![[dbg:[0-9]+]]
+; CHECK-NEXT: %0 = getelementptr inbounds i32, i32* %a, i64 1, !dbg ![[dbg:[0-9]+]]
+; CHECK-NEXT: store i32 %.sink, i32* %0, align 4, !dbg ![[dbg:[0-9]+]]
+
+; CHECK-DAG: ![[dbg]] = !DILocation(line: 0, scope: ![[scp:[0-9]+]]
+; CHECK-DAG: ![[scp]] = distinct !DILexicalBlock(scope: ![[fun:[0-9]+]]
+; CHECK-DAG: ![[fun]] = distinct !DISubprogram(name: "fun",
+
+define void @_Z3funPii(i32* nocapture noundef writeonly %a, i32 noundef %cond) !dbg !7 {
+entry:
+  call void @llvm.dbg.value(metadata i32* %a, metadata !13, metadata !DIExpression()), !dbg !15
+  call void @llvm.dbg.value(metadata i32 %cond, metadata !14, metadata !DIExpression()), !dbg !15
+  %tobool.not = icmp eq i32 %cond, 0, !dbg !16
+  br i1 %tobool.not, label %if.else, label %if.then, !dbg !18
+
+if.then:                                          ; preds = %entry
+  %arrayidx = getelementptr inbounds i32, i32* %a, i64 1, !dbg !19
+  store i32 1, i32* %arrayidx, align 4, !dbg !20
+  br label %if.end, !dbg !19
+
+if.else:                                          ; preds = %entry
+  %arrayidx1 = getelementptr inbounds i32, i32* %a, i64 1, !dbg !25
+  store i32 2, i32* %arrayidx1, align 4, !dbg !26
+  br label %if.end
+
+if.end:                                           ; preds = %if.else, %if.then
+  ret void, !dbg !27
+}
+
+declare void @llvm.dbg.value(metadata, metadata, metadata)
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!2, !3, !4, !5}
+!llvm.ident = !{!6}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus_14, file: !1, producer: "clang version 14.0.0", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, splitDebugInlining: false, nameTableKind: None)
+!1 = !DIFile(filename: "test.cpp", directory: "/")
+!2 = !{i32 7, !"Dwarf Version", i32 5}
+!3 = !{i32 2, !"Debug Info Version", i32 3}
+!4 = !{i32 1, !"wchar_size", i32 4}
+!5 = !{i32 7, !"uwtable", i32 1}
+!6 = !{!"clang version 14.0.0"}
+!7 = distinct !DISubprogram(name: "fun", linkageName: "_Z3funPii", scope: !1, file: !1, line: 1, type: !8, scopeLine: 1, flags: DIFlagPrototyped | DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !12)
+!8 = !DISubroutineType(types: !9)
+!9 = !{null, !10, !11}
+!10 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !11, size: 64)
+!11 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!12 = !{!13, !14}
+!13 = !DILocalVariable(name: "a", arg: 1, scope: !7, file: !1, line: 1, type: !10)
+!14 = !DILocalVariable(name: "cond", arg: 2, scope: !7, file: !1, line: 1, type: !11)
+!15 = !DILocation(line: 0, scope: !7)
+!16 = !DILocation(line: 2, column: 7, scope: !17)
+!17 = distinct !DILexicalBlock(scope: !7, file: !1, line: 2, column: 7)
+!18 = !DILocation(line: 2, column: 7, scope: !7)
+!19 = !DILocation(line: 3, column: 5, scope: !17)
+!20 = !DILocation(line: 3, column: 10, scope: !17)
+!25 = !DILocation(line: 5, column: 5, scope: !17)
+!26 = !DILocation(line: 5, column: 10, scope: !17)
+!27 = !DILocation(line: 6, column: 1, scope: !7)