[llvm] [LoopUnroll] Remove redundant debug instructions after blocks have been merged (PR #91246)

[via llvm-commits]

https://github.com/coderchenlin updated https://github.com/llvm/llvm-project/pull/91246

>From 7a91ca1e8c6fc07a9e177d6fe74fa384f6d43386 Mon Sep 17 00:00:00 2001
From: chenlin <chenlin138 at huawei.com>
Date: Tue, 7 May 2024 01:35:18 +0800
Subject: [PATCH] [LoopUnroll] Remove repeated debug instructions after blocks
 have been merged into the predecessor, It can reduce some compile time in
 some cases. This change only fixes the situation of loop unrolling, and other
 situations are not considered. "RemoveRedundantDbgInstrs" seems to be very
 time-consuming. Thus, we call 'RemoveRedundantDbgInstrs' in
 'simplifyLoopAfterUnroll'.

fixes: https://github.com/llvm/llvm-project/issues/89073
---
 llvm/lib/Transforms/Utils/LoopUnroll.cpp      |  4 ++
 .../LoopUnroll/unroll-remove-redundant-dbg.ll | 46 +++++++++++++++++++
 2 files changed, 50 insertions(+)
 create mode 100644 llvm/test/Transforms/LoopUnroll/unroll-remove-redundant-dbg.ll

diff --git a/llvm/lib/Transforms/Utils/LoopUnroll.cpp b/llvm/lib/Transforms/Utils/LoopUnroll.cpp
index 20978cf2e748a..1216538195fbd 100644
--- a/llvm/lib/Transforms/Utils/LoopUnroll.cpp
+++ b/llvm/lib/Transforms/Utils/LoopUnroll.cpp
@@ -377,6 +377,10 @@ void llvm::simplifyLoopAfterUnroll(Loop *L, bool SimplifyIVs, LoopInfo *LI,
   const DataLayout &DL = L->getHeader()->getModule()->getDataLayout();
   SmallVector<WeakTrackingVH, 16> DeadInsts;
   for (BasicBlock *BB : L->getBlocks()) {
+    // Remove repeated debug instructions after loop unrolling.
+    if (BB->getParent()->getSubprogram())
+      RemoveRedundantDbgInstrs(BB);
+
     for (Instruction &Inst : llvm::make_early_inc_range(*BB)) {
       if (Value *V = simplifyInstruction(&Inst, {DL, nullptr, DT, AC}))
         if (LI->replacementPreservesLCSSAForm(&Inst, V))
diff --git a/llvm/test/Transforms/LoopUnroll/unroll-remove-redundant-dbg.ll b/llvm/test/Transforms/LoopUnroll/unroll-remove-redundant-dbg.ll
new file mode 100644
index 0000000000000..8eeb10712c18f
--- /dev/null
+++ b/llvm/test/Transforms/LoopUnroll/unroll-remove-redundant-dbg.ll
@@ -0,0 +1,46 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt < %s -S -passes=loop-unroll | FileCheck %s
+
+define i64 @d(i1 %tobool.not, i32 %add, i64 %conv23) !dbg !14{
+entry:
+  br label %for.body
+
+for.body:                                         ; preds = %for.body, %entry
+  ; There should be only one "llvm.dbg.vale" after loop unrolling
+  ; CHECK: call void @llvm.dbg.value
+  ; CHECK-NOT: call void @llvm.dbg.value
+
+  %k.045 = phi i64 [ 0, %entry ], [ %k.046, %for.body ]
+  tail call void @llvm.dbg.value(metadata i32 0, metadata !13, metadata !DIExpression()), !dbg !17
+  %k.046 = add nuw nsw i64 %k.045, 1
+  %exitcond = icmp ne i64 %k.046, 5
+  br i1 %exitcond, label %for.body, label %for.end22
+
+for.end22:                                        ; preds = %for.body
+  ret i64 %k.046
+}
+
+; Function Attrs: nocallback nofree nosync nounwind speculatable willreturn memory(none)
+declare void @llvm.dbg.value(metadata, metadata, metadata)
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!12}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C89, file: !1, producer: "clang version 19.0.0git (https://github.com/llvm/llvm-project.git ec062f5b33ed22c61742e3c1486f6cba915801e0)", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, globals: !2, splitDebugInlining: false, nameTableKind: None)
+!1 = !DIFile(filename: "unroll-remove-redundant-dbg.c", directory: "", checksumkind: CSK_MD5, checksum: "aa30a1d8c04deb9b0f3885c258d2b674")
+!2 = !{!3, !8, !10}
+!3 = !DIGlobalVariableExpression(var: !4, expr: !DIExpression())
+!4 = distinct !DIGlobalVariable(name: "a", scope: !0, file: !1, line: 2, type: !5, isLocal: false, isDefinition: true)
+!5 = !DIDerivedType(tag: DW_TAG_typedef, name: "uint32_t", file: !6, line: 198, baseType: !7)
+!6 = !DIFile(filename: "/usr/include/stdint.h", directory: "", checksumkind: CSK_MD5, checksum: "da031bcff2d0c1d65aa92e7e68a44ef3")
+!7 = !DIBasicType(name: "unsigned int", size: 32, encoding: DW_ATE_unsigned)
+!8 = !DIGlobalVariableExpression(var: !9, expr: !DIExpression())
+!9 = distinct !DIGlobalVariable(name: "c", scope: !0, file: !1, line: 2, type: !5, isLocal: false, isDefinition: true)
+!10 = !DIGlobalVariableExpression(var: !11, expr: !DIExpression())
+!11 = distinct !DIGlobalVariable(name: "b", scope: !0, file: !1, line: 2, type: !5, isLocal: false, isDefinition: true)
+!12 = !{i32 2, !"Debug Info Version", i32 3}
+!13 = !DILocalVariable(name: "f", scope: !14, file: !1, line: 4, type: !5)
+!14 = distinct !DISubprogram(name: "d", scope: !1, file: !1, line: 3, type: !15, scopeLine: 3, flags: DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !16)
+!15 = !DISubroutineType(types: !16)
+!16 = !{}
+!17 = !DILocation(line: 0, scope: !14)