[Reassociate] Apply Debugloc to instrs produced when optimizing add (llvm#134676)

SLTozer · web-flow · commit 84fde791a1f2 · 2025-04-08T17:02:16.000+01:00
Currently in Reassociate we may create a set of new instructions when optimizing an `add`, but we do not set DebugLocs on the new instructions; this patch propagates the add's DebugLoc to the new instructions. Found using llvm#107279.
diff --git a/llvm/lib/Transforms/Scalar/Reassociate.cpp b/llvm/lib/Transforms/Scalar/Reassociate.cpp
@@ -1086,13 +1086,15 @@ static unsigned FindInOperandList(const SmallVectorImpl<ValueEntry> &Ops,
 
 /// Emit a tree of add instructions, summing Ops together
 /// and returning the result.  Insert the tree before I.
-static Value *EmitAddTreeOfValues(BasicBlock::iterator It,
+static Value *EmitAddTreeOfValues(Instruction *I,
                                   SmallVectorImpl<WeakTrackingVH> &Ops) {
   if (Ops.size() == 1) return Ops.back();
 
   Value *V1 = Ops.pop_back_val();
-  Value *V2 = EmitAddTreeOfValues(It, Ops);
-  return CreateAdd(V2, V1, "reass.add", It, &*It);
+  Value *V2 = EmitAddTreeOfValues(I, Ops);
+  auto *NewAdd = CreateAdd(V2, V1, "reass.add", I->getIterator(), I);
+  NewAdd->setDebugLoc(I->getDebugLoc());
+  return NewAdd;
 }
 
 /// If V is an expression tree that is a multiplication sequence,
@@ -1682,7 +1684,7 @@ Value *ReassociatePass::OptimizeAdd(Instruction *I,
     DummyInst->deleteValue();
 
     unsigned NumAddedValues = NewMulOps.size();
-    Value *V = EmitAddTreeOfValues(I->getIterator(), NewMulOps);
+    Value *V = EmitAddTreeOfValues(I, NewMulOps);
 
     // Now that we have inserted the add tree, optimize it. This allows us to
     // handle cases that require multiple factoring steps, such as this:
@@ -1694,6 +1696,7 @@ Value *ReassociatePass::OptimizeAdd(Instruction *I,
 
     // Create the multiply.
     Instruction *V2 = CreateMul(V, MaxOccVal, "reass.mul", I->getIterator(), I);
+    V2->setDebugLoc(I->getDebugLoc());
 
     // Rerun associate on the multiply in case the inner expression turned into
     // a multiply.  We want to make sure that we keep things in canonical form.
diff --git a/llvm/test/Transforms/Reassociate/debugloc-reass-add.ll b/llvm/test/Transforms/Reassociate/debugloc-reass-add.ll
@@ -0,0 +1,56 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
+; RUN: opt -p=reassociate -S < %s | FileCheck %s
+
+;; Tests that when we reassociate %add93, we apply its debug location to the new
+;; instructions.
+
+define void @foo(i32 %0) {
+; CHECK-LABEL: define void @foo(
+; CHECK-SAME: i32 [[TMP0:%.*]]) {
+; CHECK-NEXT:  [[ENTRY:.*:]]
+; CHECK-NEXT:    br label %[[FOR_COND23:.*]]
+; CHECK:       [[FOR_COND23]]:
+; CHECK-NEXT:    [[SUB59:%.*]] = sub i32 0, 0
+; CHECK-NEXT:    [[MUL68:%.*]] = mul i32 0, [[TMP0]]
+; CHECK-NEXT:    [[REASS_ADD:%.*]] = add i32 [[MUL68]], [[TMP0]], !dbg [[DBG3:![0-9]+]]
+; CHECK-NEXT:    [[REASS_MUL1:%.*]] = mul i32 [[REASS_ADD]], [[SUB59]], !dbg [[DBG3]]
+; CHECK-NEXT:    [[REASS_MUL:%.*]] = add i32 [[REASS_MUL1]], 1, !dbg [[DBG3]]
+; CHECK-NEXT:    [[CONV95:%.*]] = trunc i32 [[REASS_MUL]] to i16
+; CHECK-NEXT:    store i16 [[CONV95]], ptr null, align 2
+; CHECK-NEXT:    br label %[[FOR_COND23]]
+;
+entry:
+  br label %for.cond23
+
+for.cond23:                                       ; preds = %for.cond23, %entry
+  %sub59 = sub i32 0, 0
+  %mul62 = mul i32 %sub59, %0
+  %mul68 = mul i32 %mul62, 0
+  %mul77 = mul i32 %sub59, %0
+  %add84 = or i32 %mul68, %mul77
+  %add93 = add i32 %add84, 1, !dbg !4
+  %conv95 = trunc i32 %add93 to i16
+  store i16 %conv95, ptr null, align 2
+  br label %for.cond23
+}
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!3}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C11, file: !1, producer: "clang version 20.0.0git")
+!1 = !DIFile(filename: "test.c", directory: "/tmp")
+!2 = !{}
+!3 = !{i32 2, !"Debug Info Version", i32 3}
+!4 = !DILocation(line: 15, column: 50, scope: !5)
+!5 = distinct !DISubprogram(name: "foo", scope: !1, file: !1, line: 14, type: !6, scopeLine: 14, unit: !0, retainedNodes: !2)
+!6 = distinct !DISubroutineType(types: !7)
+!7 = !{null}
+;.
+; CHECK: [[META0:![0-9]+]] = distinct !DICompileUnit(language: DW_LANG_C11, file: [[META1:![0-9]+]], producer: "{{.*}}clang version {{.*}}", isOptimized: false, runtimeVersion: 0, emissionKind: NoDebug)
+; CHECK: [[META1]] = !DIFile(filename: "test.c", directory: {{.*}})
+; CHECK: [[DBG3]] = !DILocation(line: 15, column: 50, scope: [[META4:![0-9]+]])
+; CHECK: [[META4]] = distinct !DISubprogram(name: "foo", scope: [[META1]], file: [[META1]], line: 14, type: [[META5:![0-9]+]], scopeLine: 14, spFlags: DISPFlagDefinition, unit: [[META0]], retainedNodes: [[META7:![0-9]+]])
+; CHECK: [[META5]] = distinct !DISubroutineType(types: [[META6:![0-9]+]])
+; CHECK: [[META6]] = !{null}
+; CHECK: [[META7]] = !{}
+;.
