[llvm] [DebugInfo][InstCombine] When replacing bswap idiom, add DebugLoc to new insts (PR #114231)

[Stephen Tozer via llvm-commits]

https://github.com/SLTozer created https://github.com/llvm/llvm-project/pull/114231

Currently when InstCombineAndOrXor recognizes a bswap idiom and replaces it with an intrinsic and other instructions, only the last instruction gets the DebugLoc of the replaced instruction set to it. This patch applies the DebugLoc to all the generated instructions, to maintain some degree of attribution.

>From 5b810a9a0afd92ca1cb10ee76f29c0d3b61b2696 Mon Sep 17 00:00:00 2001
From: Stephen Tozer <stephen.tozer at sony.com>
Date: Thu, 24 Oct 2024 15:38:26 +0100
Subject: [PATCH] [DebugInfo][InstCombine] When replacing bswap idiom, add
 DebugLoc to new insts

Currently when InstCombineAndOrXor recognizes a bswap idiom and replaces it
with an intrinsic and other instructions, only the last instruction gets the
DebugLoc of the replaced instruction set to it. This patch applies the
DebugLoc to all the generated instructions, to maintain some degree of
attribution.
---
 .../InstCombine/InstCombineAndOrXor.cpp       |  4 +-
 .../Transforms/InstCombine/debugloc-bswap.ll  | 52 +++++++++++++++++++
 2 files changed, 55 insertions(+), 1 deletion(-)
 create mode 100644 llvm/test/Transforms/InstCombine/debugloc-bswap.ll

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp b/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
index 50d1c61c24cf47..e2eae7fb8327cc 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
@@ -2879,8 +2879,10 @@ Instruction *InstCombinerImpl::matchBSwapOrBitReverse(Instruction &I,
   Instruction *LastInst = Insts.pop_back_val();
   LastInst->removeFromParent();
 
-  for (auto *Inst : Insts)
+  for (auto *Inst : Insts) {
+    Inst->setDebugLoc(I.getDebugLoc());
     Worklist.push(Inst);
+  }
   return LastInst;
 }
 
diff --git a/llvm/test/Transforms/InstCombine/debugloc-bswap.ll b/llvm/test/Transforms/InstCombine/debugloc-bswap.ll
new file mode 100644
index 00000000000000..6ac82878f9c201
--- /dev/null
+++ b/llvm/test/Transforms/InstCombine/debugloc-bswap.ll
@@ -0,0 +1,52 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
+; RUN: opt -passes=instcombine -S %s -o - | FileCheck %s
+;; Tests that when InstCombine replaces a bswap idiom with an intrinsic, the
+;; !dbg attachment from the replaced instruction is applied to all generated
+;; instructions, not just the last.
+
+target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-i128:128-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+define i32 @inflate(ptr %strm) {
+; CHECK-LABEL: define i32 @inflate(
+; CHECK-SAME: ptr [[STRM:%.*]]) {
+; CHECK-NEXT:  [[ENTRY:.*:]]
+; CHECK-NEXT:    [[TMP0:%.*]] = load i64, ptr [[STRM]], align 8
+; CHECK-NEXT:    [[TRUNC:%.*]] = trunc i64 [[TMP0]] to i32, !dbg [[DBG3:![0-9]+]]
+; CHECK-NEXT:    [[TMP1:%.*]] = and i32 [[TRUNC]], 65535, !dbg [[DBG3]]
+; CHECK-NEXT:    [[MASK:%.*]] = call i32 @llvm.bswap.i32(i32 [[TMP1]]), !dbg [[DBG3]]
+; CHECK-NEXT:    [[ADD665:%.*]] = zext i32 [[MASK]] to i64, !dbg [[DBG3]]
+; CHECK-NEXT:    store i64 [[ADD665]], ptr [[STRM]], align 8
+; CHECK-NEXT:    ret i32 0
+;
+entry:
+  %0 = load i64, ptr %strm, align 8
+  %and660 = and i64 %0, 65280
+  %shl661 = shl i64 %and660, 8
+  %and663 = and i64 %0, 255
+  %shl664 = shl i64 %and663, 24
+  %add665 = or i64 %shl661, %shl664, !dbg !4
+  store i64 %add665, ptr %strm, align 8
+  ret i32 0
+}
+
+!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: "/tmp/zlib_inflate.c", directory: "/tmp")
+!2 = !{}
+!3 = !{i32 2, !"Debug Info Version", i32 3}
+!4 = !DILocation(line: 8, column: 42, scope: !6)
+!5 = !DIFile(filename: "zlib_inflate.c", directory: "/tmp")
+!6 = distinct !DISubprogram(name: "inflate", scope: !5, file: !5, line: 622, type: !7, scopeLine: 625, unit: !0, retainedNodes: !2)
+!7 = distinct !DISubroutineType(types: !2)
+;.
+; 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: "/tmp/zlib_inflate.c", directory: {{.*}})
+; CHECK: [[DBG3]] = !DILocation(line: 8, column: 42, scope: [[META4:![0-9]+]])
+; CHECK: [[META4]] = distinct !DISubprogram(name: "inflate", scope: [[META5:![0-9]+]], file: [[META5]], line: 622, type: [[META6:![0-9]+]], scopeLine: 625, spFlags: DISPFlagDefinition, unit: [[META0]], retainedNodes: [[META7:![0-9]+]])
+; CHECK: [[META5]] = !DIFile(filename: "zlib_inflate.c", directory: {{.*}})
+; CHECK: [[META6]] = distinct !DISubroutineType(types: [[META7]])
+; CHECK: [[META7]] = !{}
+;.