[DebugInfo][InstCombine] When replacing bswap idiom, add DebugLoc to new insts (#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.

Author: SLTozer

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;
 }
 

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]] = !{}
+;.