[llvm] [DebugInfo][IndVarSimplify] Propagate source loc when simplifying rem (PR #135399)

[Stephen Tozer via llvm-commits]

https://github.com/SLTozer created https://github.com/llvm/llvm-project/pull/135399

When IndVarSimplify simplifies a rem of the induction variable to a cmp and select, only the select currently receives the rem's source location; this patch propagates it to the cmp as well.

Found using https://github.com/llvm/llvm-project/pull/107279.

>From 1fe84ba36e5d956f61f51a9289446adee7385ac4 Mon Sep 17 00:00:00 2001
From: Stephen Tozer <Stephen.Tozer at sony.com>
Date: Wed, 9 Apr 2025 17:52:28 +0100
Subject: [PATCH] [DebugInfo][IndVarSimplify] Propagate source loc when
 simplifying rem

When IndVarSimplify simplifies a rem of the induction variable to a cmp
and select, only the select currently receives the rem's source location;
this patch propagates it to the select as well.

Found using https://github.com/llvm/llvm-project/pull/107279.
---
 llvm/lib/Transforms/Utils/SimplifyIndVar.cpp  |  1 +
 .../IndVarSimplify/debugloc-rem-subst.ll      | 59 +++++++++++++++++++
 2 files changed, 60 insertions(+)
 create mode 100644 llvm/test/Transforms/IndVarSimplify/debugloc-rem-subst.ll

diff --git a/llvm/lib/Transforms/Utils/SimplifyIndVar.cpp b/llvm/lib/Transforms/Utils/SimplifyIndVar.cpp
index 5a76bec017655..03dbf9513d140 100644
--- a/llvm/lib/Transforms/Utils/SimplifyIndVar.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyIndVar.cpp
@@ -350,6 +350,7 @@ void SimplifyIndvar::replaceRemWithNumeratorOrZero(BinaryOperator *Rem) {
   auto *T = Rem->getType();
   auto *N = Rem->getOperand(0), *D = Rem->getOperand(1);
   ICmpInst *ICmp = new ICmpInst(Rem->getIterator(), ICmpInst::ICMP_EQ, N, D);
+  ICmp->setDebugLoc(Rem->getDebugLoc());
   SelectInst *Sel =
       SelectInst::Create(ICmp, ConstantInt::get(T, 0), N, "iv.rem", Rem->getIterator());
   Rem->replaceAllUsesWith(Sel);
diff --git a/llvm/test/Transforms/IndVarSimplify/debugloc-rem-subst.ll b/llvm/test/Transforms/IndVarSimplify/debugloc-rem-subst.ll
new file mode 100644
index 0000000000000..121eec75c1b3c
--- /dev/null
+++ b/llvm/test/Transforms/IndVarSimplify/debugloc-rem-subst.ll
@@ -0,0 +1,59 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
+; RUN: opt < %s -p=indvars -S | FileCheck %s
+
+;; When that when IndVarSimplify simplifies the rem to a cmp and select, we
+;; propagate the rem's source location to both the new instructions.
+
+define i32 @widget() !dbg !5 {
+; CHECK-LABEL: define i32 @widget(
+; CHECK-SAME: ) !dbg [[DBG5:![0-9]+]] {
+; CHECK-NEXT:  [[BB:.*:]]
+; CHECK-NEXT:    br label %[[BB1:.*]]
+; CHECK:       [[BB1_LOOPEXIT:.*]]:
+; CHECK-NEXT:    br label %[[BB1]]
+; CHECK:       [[BB1]]:
+; CHECK-NEXT:    br label %[[BB2:.*]]
+; CHECK:       [[BB2]]:
+; CHECK-NEXT:    [[PHI:%.*]] = phi i32 [ 0, %[[BB1]] ], [ [[ADD:%.*]], %[[BB2]] ]
+; CHECK-NEXT:    [[ADD]] = add nuw nsw i32 1, [[PHI]]
+; CHECK-NEXT:    [[TMP0:%.*]] = icmp eq i32 [[ADD]], 3, !dbg [[DBG8:![0-9]+]]
+; CHECK-NEXT:    [[IV_REM:%.*]] = select i1 [[TMP0]], i32 0, i32 [[ADD]], !dbg [[DBG8]]
+; CHECK-NEXT:    [[ZEXT:%.*]] = zext i32 [[IV_REM]] to i64
+; CHECK-NEXT:    br i1 false, label %[[BB2]], label %[[BB1_LOOPEXIT]]
+;
+bb:
+  br label %bb1
+
+bb1:                                              ; preds = %bb2, %bb
+  br label %bb2
+
+bb2:                                              ; preds = %bb2, %bb1
+  %phi = phi i32 [ 0, %bb1 ], [ %add, %bb2 ]
+  %add = add i32 1, %phi
+  %urem = urem i32 %add, 3, !dbg !8
+  %zext = zext i32 %urem to i64
+  %icmp = icmp ult i32 %phi, 2
+  br i1 %icmp, label %bb2, label %bb1
+}
+
+!llvm.dbg.cu = !{!0}
+!llvm.debugify = !{!2, !3}
+!llvm.module.flags = !{!4}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C, file: !1, producer: "debugify", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug)
+!1 = !DIFile(filename: "llvm/test/Transforms/IndVarSimplify/debugloc-rem-subst.ll", directory: "/")
+!2 = !{i32 8}
+!3 = !{i32 0}
+!4 = !{i32 2, !"Debug Info Version", i32 3}
+!5 = distinct !DISubprogram(name: "widget", linkageName: "widget", scope: null, file: !1, line: 1, type: !6, scopeLine: 1, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0)
+!6 = !DISubroutineType(types: !7)
+!7 = !{}
+!8 = !DILocation(line: 1, column: 1, scope: !5)
+;.
+; CHECK: [[META0:![0-9]+]] = distinct !DICompileUnit(language: DW_LANG_C, file: [[META1:![0-9]+]], producer: "debugify", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug)
+; CHECK: [[META1]] = !DIFile(filename: "llvm/test/Transforms/IndVarSimplify/debugloc-rem-subst.ll", directory: {{.*}})
+; CHECK: [[DBG5]] = distinct !DISubprogram(name: "widget", linkageName: "widget", scope: null, file: [[META1]], line: 1, type: [[META6:![0-9]+]], scopeLine: 1, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: [[META0]])
+; CHECK: [[META6]] = !DISubroutineType(types: [[META7:![0-9]+]])
+; CHECK: [[META7]] = !{}
+; CHECK: [[DBG8]] = !DILocation(line: 1, column: 1, scope: [[DBG5]])
+;.