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

Remove redundant 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 just add here after the "Dest" has been
merged into the "Fold", this may be a more targeted solution!!!

fixes: #89073

Author: coderchenlin

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))

llvm/test/Transforms/LoopUnroll/unroll-remove-redundant-dbg.ll

@@ -0,0 +1,50 @@
+; 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{
+; There should be only one "llvm.dbg.vale" after loop unrolling
+; CHECK-LABEL: @d(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    br label [[FOR_BODY:%.*]]
+; CHECK:       for.body:
+; CHECK-NEXT:    tail call void @llvm.dbg.value(metadata i32 0, metadata [[META16:![0-9]+]], metadata !DIExpression()), !dbg [[DBG17:![0-9]+]]
+; CHECK-NEXT:    ret i64 5
+;
+entry:
+  br label %for.body
+
+for.body:                                         ; preds = %for.body, %entry
+  %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)