[llvm] 739fa1c - [indvars] Missing variables at Og: (#69920)
via llvm-commits
llvm-commits at lists.llvm.org
Sun Apr 7 21:32:00 PDT 2024
Author: Carlos Alberto Enciso
Date: 2024-04-08T05:31:56+01:00
New Revision: 739fa1c84b92b8af7dceedf2e5ad808a64e85a57
URL: https://github.com/llvm/llvm-project/commit/739fa1c84b92b8af7dceedf2e5ad808a64e85a57
DIFF: https://github.com/llvm/llvm-project/commit/739fa1c84b92b8af7dceedf2e5ad808a64e85a57.diff
LOG: [indvars] Missing variables at Og: (#69920)
https://bugs.llvm.org/show_bug.cgi?id=51735
https://github.com/llvm/llvm-project/issues/51077
In the given test case:
```
4 ...
5 void bar() {
6 int End = 777;
7 int Index = 27;
8 char Var = 1;
9 for (; Index < End; ++Index)
10 ;
11 nop(Index);
12 }
13 ...
```
Missing local variable `Index` after loop `Induction Variable Elimination`. When adding a breakpoint at line `11`, LLDB does not have information on the variable. But it has info on `Var` and `End`.
Added:
llvm/test/Transforms/IndVarSimplify/pr51735-1.ll
llvm/test/Transforms/IndVarSimplify/pr51735-2.ll
llvm/test/Transforms/IndVarSimplify/pr51735-3.ll
llvm/test/Transforms/IndVarSimplify/pr51735.ll
Modified:
llvm/include/llvm/Support/GenericLoopInfo.h
llvm/include/llvm/Transforms/Utils/LoopUtils.h
llvm/lib/Transforms/Utils/LoopUtils.cpp
Removed:
################################################################################
diff --git a/llvm/include/llvm/Support/GenericLoopInfo.h b/llvm/include/llvm/Support/GenericLoopInfo.h
index d560ca648132c9..f4b50367bf93d7 100644
--- a/llvm/include/llvm/Support/GenericLoopInfo.h
+++ b/llvm/include/llvm/Support/GenericLoopInfo.h
@@ -44,6 +44,8 @@
#include "llvm/ADT/PostOrderIterator.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/SetOperations.h"
+#include "llvm/IR/IntrinsicInst.h"
+#include "llvm/IR/ValueHandle.h"
#include "llvm/Support/Allocator.h"
#include "llvm/Support/GenericDomTree.h"
@@ -75,6 +77,13 @@ template <class BlockT, class LoopT> class LoopBase {
const LoopBase<BlockT, LoopT> &
operator=(const LoopBase<BlockT, LoopT> &) = delete;
+ // Induction variable exit value and its debug users, preserved by the
+ // 'indvars' pass, when it detects that the loop can be deleted and the
+ // there are no PHIs to be rewritten.
+ // For now, we only preserve single induction variables.
+ Value *IndVarFinalValue = nullptr;
+ SmallVector<WeakVH> IndVarDebugUsers;
+
public:
/// Return the nesting level of this loop. An outer-most loop has depth 1,
/// for consistency with loop depth values used for basic blocks, where depth
@@ -251,6 +260,21 @@ template <class BlockT, class LoopT> class LoopBase {
[&](BlockT *Pred) { return contains(Pred); });
}
+ /// Preserve the induction variable exit value and its debug users by the
+ /// 'indvars' pass if the loop can deleted. Those debug users will be used
+ /// by the 'loop-delete' pass.
+ void preserveDebugInductionVariableInfo(
+ Value *FinalValue, SmallVector<DbgVariableIntrinsic *> DbgUsers) {
+ IndVarFinalValue = FinalValue;
+ for (DbgVariableIntrinsic *DebugUser : DbgUsers)
+ IndVarDebugUsers.push_back(DebugUser);
+ }
+
+ Value *getDebugInductionVariableFinalValue() { return IndVarFinalValue; }
+ SmallVector<WeakVH> &getDebugInductionVariableDebugUsers() {
+ return IndVarDebugUsers;
+ }
+
//===--------------------------------------------------------------------===//
// APIs for simple analysis of the loop.
//
diff --git a/llvm/include/llvm/Transforms/Utils/LoopUtils.h b/llvm/include/llvm/Transforms/Utils/LoopUtils.h
index 345e09dce0b2b1..15b230ba92ddaa 100644
--- a/llvm/include/llvm/Transforms/Utils/LoopUtils.h
+++ b/llvm/include/llvm/Transforms/Utils/LoopUtils.h
@@ -468,6 +468,12 @@ int rewriteLoopExitValues(Loop *L, LoopInfo *LI, TargetLibraryInfo *TLI,
ReplaceExitVal ReplaceExitValue,
SmallVector<WeakTrackingVH, 16> &DeadInsts);
+/// Assign exit values to variables that use this loop variable during the loop.
+void addDebugValuesToIncomingValue(BasicBlock *Successor, Value *IndVar,
+ PHINode *PN);
+void addDebugValuesToLoopVariable(BasicBlock *Successor, Value *ExitValue,
+ PHINode *PN);
+
/// Set weights for \p UnrolledLoop and \p RemainderLoop based on weights for
/// \p OrigLoop and the following distribution of \p OrigLoop iteration among \p
/// UnrolledLoop and \p RemainderLoop. \p UnrolledLoop receives weights that
diff --git a/llvm/lib/Transforms/Utils/LoopUtils.cpp b/llvm/lib/Transforms/Utils/LoopUtils.cpp
index 9d816c5220532c..4187bd38cf29ac 100644
--- a/llvm/lib/Transforms/Utils/LoopUtils.cpp
+++ b/llvm/lib/Transforms/Utils/LoopUtils.cpp
@@ -31,6 +31,7 @@
#include "llvm/Analysis/ScalarEvolutionAliasAnalysis.h"
#include "llvm/Analysis/ScalarEvolutionExpressions.h"
#include "llvm/IR/DIBuilder.h"
+#include "llvm/IR/DebugInfo.h"
#include "llvm/IR/Dominators.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/IntrinsicInst.h"
@@ -608,6 +609,17 @@ void llvm::deleteDeadLoop(Loop *L, DominatorTree *DT, ScalarEvolution *SE,
llvm::SmallVector<DbgVariableRecord *, 4> DeadDbgVariableRecords;
if (ExitBlock) {
+ if (ExitBlock->phis().empty()) {
+ // As the loop is deleted, replace the debug users with the preserved
+ // induction variable final value recorded by the 'indvar' pass.
+ Value *FinalValue = L->getDebugInductionVariableFinalValue();
+ SmallVector<WeakVH> &DbgUsers = L->getDebugInductionVariableDebugUsers();
+ for (WeakVH &DebugUser : DbgUsers)
+ if (DebugUser)
+ cast<DbgVariableIntrinsic>(DebugUser)->replaceVariableLocationOp(
+ 0u, FinalValue);
+ }
+
// Given LCSSA form is satisfied, we should not have users of instructions
// within the dead loop outside of the loop. However, LCSSA doesn't take
// unreachable uses into account. We handle them here.
@@ -1401,6 +1413,36 @@ static bool checkIsIndPhi(PHINode *Phi, Loop *L, ScalarEvolution *SE,
return InductionDescriptor::isInductionPHI(Phi, L, SE, ID);
}
+void llvm::addDebugValuesToIncomingValue(BasicBlock *Successor, Value *IndVar,
+ PHINode *PN) {
+ SmallVector<DbgVariableIntrinsic *> DbgUsers;
+ findDbgUsers(DbgUsers, IndVar);
+ for (auto *DebugUser : DbgUsers) {
+ // Skip debug-users with variadic variable locations; they will not,
+ // get updated, which is fine as that is the existing behaviour.
+ if (DebugUser->hasArgList())
+ continue;
+ auto *Cloned = cast<DbgVariableIntrinsic>(DebugUser->clone());
+ Cloned->replaceVariableLocationOp(0u, PN);
+ Cloned->insertBefore(*Successor, Successor->getFirstNonPHIIt());
+ }
+}
+
+void llvm::addDebugValuesToLoopVariable(BasicBlock *Successor, Value *ExitValue,
+ PHINode *PN) {
+ SmallVector<DbgVariableIntrinsic *> DbgUsers;
+ findDbgUsers(DbgUsers, PN);
+ for (auto *DebugUser : DbgUsers) {
+ // Skip debug-users with variadic variable locations; they will not,
+ // get updated, which is fine as that is the existing behaviour.
+ if (DebugUser->hasArgList())
+ continue;
+ auto *Cloned = cast<DbgVariableIntrinsic>(DebugUser->clone());
+ Cloned->replaceVariableLocationOp(0u, ExitValue);
+ Cloned->insertBefore(*Successor, Successor->getFirstNonPHIIt());
+ }
+}
+
int llvm::rewriteLoopExitValues(Loop *L, LoopInfo *LI, TargetLibraryInfo *TLI,
ScalarEvolution *SE,
const TargetTransformInfo *TTI,
@@ -1542,6 +1584,10 @@ int llvm::rewriteLoopExitValues(Loop *L, LoopInfo *LI, TargetLibraryInfo *TLI,
(isa<PHINode>(Inst) || isa<LandingPadInst>(Inst)) ?
&*Inst->getParent()->getFirstInsertionPt() : Inst;
RewritePhiSet.emplace_back(PN, i, ExitValue, InsertPt, HighCost);
+
+ // Add debug values for the candidate PHINode incoming value.
+ if (BasicBlock *Successor = ExitBB->getSingleSuccessor())
+ addDebugValuesToIncomingValue(Successor, PN->getIncomingValue(i), PN);
}
}
}
@@ -1600,11 +1646,30 @@ int llvm::rewriteLoopExitValues(Loop *L, LoopInfo *LI, TargetLibraryInfo *TLI,
// Replace PN with ExitVal if that is legal and does not break LCSSA.
if (PN->getNumIncomingValues() == 1 &&
LI->replacementPreservesLCSSAForm(PN, ExitVal)) {
+ addDebugValuesToLoopVariable(PN->getParent(), ExitVal, PN);
PN->replaceAllUsesWith(ExitVal);
PN->eraseFromParent();
}
}
+ // If the loop can be deleted and there are no PHIs to be rewritten (there
+ // are no loop live-out values), record debug variables corresponding to the
+ // induction variable with their constant exit-values. Those values will be
+ // inserted by the 'deletion loop' logic.
+ if (LoopCanBeDel && RewritePhiSet.empty()) {
+ if (auto *IndVar = L->getInductionVariable(*SE)) {
+ const SCEV *PNSCEV = SE->getSCEVAtScope(IndVar, L->getParentLoop());
+ if (auto *Const = dyn_cast<SCEVConstant>(PNSCEV)) {
+ Value *FinalIVValue = Const->getValue();
+ if (L->getUniqueExitBlock()) {
+ SmallVector<DbgVariableIntrinsic *> DbgUsers;
+ findDbgUsers(DbgUsers, IndVar);
+ L->preserveDebugInductionVariableInfo(FinalIVValue, DbgUsers);
+ }
+ }
+ }
+ }
+
// The insertion point instruction may have been deleted; clear it out
// so that the rewriter doesn't trip over it later.
Rewriter.clearInsertPoint();
diff --git a/llvm/test/Transforms/IndVarSimplify/pr51735-1.ll b/llvm/test/Transforms/IndVarSimplify/pr51735-1.ll
new file mode 100644
index 00000000000000..356217985fed11
--- /dev/null
+++ b/llvm/test/Transforms/IndVarSimplify/pr51735-1.ll
@@ -0,0 +1,129 @@
+; RUN: opt -passes="loop(indvars)" \
+; RUN: --experimental-debuginfo-iterators=false -S -o - < %s | \
+; RUN: FileCheck --check-prefix=CHECK %s
+; RUN: opt -passes="loop(indvars,loop-deletion)" \
+; RUN: --experimental-debuginfo-iterators=false -S -o - < %s | \
+; RUN: FileCheck --check-prefix=CHECK %s
+
+; Make sure that when we delete the loop, that the variable Index has
+; the 777 value.
+
+; As this test case does fire the 'indvars' transformation, the debug values
+; are added to the 'for.end' exit block. No debug values are preserved by the
+; pass to be used by the 'loop-deletion' pass.
+
+; CHECK: for.cond:
+; CHECK: call void @llvm.dbg.value(metadata i32 %[[SSA_INDEX_0:.+]], metadata ![[DBG:[0-9]+]], {{.*}}
+
+; CHECK: for.extra:
+; CHECK: %[[SSA_CALL_0:.+]] = call noundef i32 @"?nop@@YAHH at Z"(i32 noundef %[[SSA_INDEX_0]]), {{.*}}
+; CHECK: br i1 %[[SSA_CMP_0:.+]], label %for.cond, label %if.else, {{.*}}
+
+; CHECK: if.then:
+; CHECK: call void @llvm.dbg.value(metadata i32 777, metadata ![[DBG]], {{.*}}
+; CHECK: call void @llvm.dbg.value(metadata i32 %[[SSA_VAR_1:.+]], metadata ![[VAR:[0-9]+]], {{.*}}
+; CHECK: br label %for.end, {{.*}}
+
+; CHECK: if.else:
+; CHECK: call void @llvm.dbg.value(metadata i32 %[[SSA_VAR_2:.+]], metadata ![[VAR:[0-9]+]], {{.*}}
+; CHECK: br label %for.end, {{.*}}
+
+; CHECK: for.end:
+; CHECK: call void @llvm.dbg.value(metadata i32 777, metadata ![[DBG]], {{.*}}
+
+; CHECK-DAG: ![[DBG]] = !DILocalVariable(name: "Index"{{.*}})
+; CHECK-DAG: ![[VAR]] = !DILocalVariable(name: "Var"{{.*}})
+
+define dso_local noundef i32 @"?nop@@YAHH at Z"(i32 noundef %Param) !dbg !11 {
+entry:
+ %Param.addr = alloca i32, align 4
+ store i32 %Param, ptr %Param.addr, align 4
+ call void @llvm.dbg.declare(metadata ptr %Param.addr, metadata !32, metadata !DIExpression()), !dbg !35
+ ret i32 0, !dbg !36
+}
+
+define dso_local void @_Z3barv() local_unnamed_addr #1 !dbg !12 {
+entry:
+ call void @llvm.dbg.value(metadata i32 777, metadata !16, metadata !DIExpression()), !dbg !17
+ call void @llvm.dbg.value(metadata i32 27, metadata !18, metadata !DIExpression()), !dbg !17
+ call void @llvm.dbg.value(metadata i32 1, metadata !19, metadata !DIExpression()), !dbg !17
+ call void @llvm.dbg.value(metadata i32 1, metadata !30, metadata !DIExpression()), !dbg !17
+ br label %for.cond, !dbg !20
+
+for.cond: ; preds = %for.cond, %entry
+ %Index.0 = phi i32 [ 27, %entry ], [ %inc, %for.extra ], !dbg !17
+ call void @llvm.dbg.value(metadata i32 %Index.0, metadata !18, metadata !DIExpression()), !dbg !17
+ %cmp = icmp ult i32 %Index.0, 777, !dbg !21
+ %inc = add nuw nsw i32 %Index.0, 1, !dbg !24
+ call void @llvm.dbg.value(metadata i32 %inc, metadata !18, metadata !DIExpression()), !dbg !17
+ br i1 %cmp, label %for.extra, label %if.then, !dbg !25, !llvm.loop !26
+
+for.extra:
+ %call.0 = call noundef i32 @"?nop@@YAHH at Z"(i32 noundef %Index.0), !dbg !21
+ %cmp.0 = icmp ult i32 %Index.0, %call.0, !dbg !21
+ br i1 %cmp.0, label %for.cond, label %if.else, !dbg !25, !llvm.loop !26
+
+if.then: ; preds = %for.cond
+ %Var.1 = add nsw i32 %Index.0, 1, !dbg !20
+ call void @llvm.dbg.value(metadata i32 %Var.1, metadata !19, metadata !DIExpression()), !dbg !20
+ br label %for.end, !dbg !20
+
+if.else:
+ %Var.2 = add nsw i32 %Index.0, 2, !dbg !20
+ call void @llvm.dbg.value(metadata i32 %Var.2, metadata !19, metadata !DIExpression()), !dbg !20
+ br label %for.end, !dbg !20
+
+for.end: ; preds = %if.else, %if.then
+ %Zeta.0 = phi i32 [ %Var.1, %if.then ], [ %Var.2, %if.else ], !dbg !20
+ call void @llvm.dbg.value(metadata i32 %Zeta.0, metadata !30, metadata !DIExpression()), !dbg !20
+ %Var.3 = add nsw i32 %Index.0, 1, !dbg !20
+ call void @llvm.dbg.value(metadata i32 %Var.3, metadata !19, metadata !DIExpression()), !dbg !20
+ %call = call noundef i32 @"?nop@@YAHH at Z"(i32 noundef %Index.0), !dbg !37
+ ret void, !dbg !29
+}
+
+declare void @llvm.dbg.value(metadata, metadata, metadata)
+declare void @llvm.dbg.declare(metadata, metadata, metadata)
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!2, !3, !4, !5, !6, !7, !8}
+!llvm.ident = !{!9}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus_14, file: !1, producer: "clang", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, splitDebugInlining: false, nameTableKind: None)
+!1 = !DIFile(filename: "test.cpp", directory: "")
+!2 = !{i32 7, !"Dwarf Version", i32 5}
+!3 = !{i32 2, !"Debug Info Version", i32 3}
+!4 = !{i32 1, !"wchar_size", i32 4}
+!5 = !{i32 8, !"PIC Level", i32 2}
+!6 = !{i32 7, !"PIE Level", i32 2}
+!7 = !{i32 7, !"uwtable", i32 2}
+!8 = !{i32 7, !"frame-pointer", i32 2}
+!9 = !{!"clang version 18.0.0"}
+!10 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!11 = distinct !DISubprogram(name: "nop", linkageName: "?nop@@YAHH at Z", scope: !1, file: !1, line: 1, type: !33, scopeLine: 1, flags: DIFlagPrototyped, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !31)
+!12 = distinct !DISubprogram(name: "bar", linkageName: "_Z3barv", scope: !1, file: !1, line: 5, type: !13, scopeLine: 5, flags: DIFlagPrototyped, spFlags: DISPFlagDefinition, unit: !0, retainedNodes: !15)
+!13 = !DISubroutineType(types: !14)
+!14 = !{null}
+!15 = !{}
+!16 = !DILocalVariable(name: "End", scope: !12, file: !1, line: 6, type: !10)
+!17 = !DILocation(line: 0, scope: !12)
+!18 = !DILocalVariable(name: "Index", scope: !12, file: !1, line: 7, type: !10)
+!19 = !DILocalVariable(name: "Var", scope: !12, file: !1, line: 8, type: !10)
+!20 = !DILocation(line: 9, column: 3, scope: !12)
+!21 = !DILocation(line: 9, column: 16, scope: !22)
+!22 = distinct !DILexicalBlock(scope: !23, file: !1, line: 9, column: 3)
+!23 = distinct !DILexicalBlock(scope: !12, file: !1, line: 9, column: 3)
+!24 = !DILocation(line: 9, column: 23, scope: !22)
+!25 = !DILocation(line: 9, column: 3, scope: !23)
+!26 = distinct !{!26, !25, !27, !28}
+!27 = !DILocation(line: 10, column: 5, scope: !23)
+!28 = !{!"llvm.loop.mustprogress"}
+!29 = !DILocation(line: 12, column: 1, scope: !12)
+!30 = !DILocalVariable(name: "Zeta", scope: !12, file: !1, line: 8, type: !10)
+!31 = !{!32}
+!32 = !DILocalVariable(name: "Param", arg: 1, scope: !11, file: !1, line: 1, type: !10)
+!33 = !DISubroutineType(types: !34)
+!34 = !{!10, !10}
+!35 = !DILocation(line: 1, scope: !11)
+!36 = !DILocation(line: 2, scope: !11)
+!37 = !DILocation(line: 20, scope: !12)
diff --git a/llvm/test/Transforms/IndVarSimplify/pr51735-2.ll b/llvm/test/Transforms/IndVarSimplify/pr51735-2.ll
new file mode 100644
index 00000000000000..58cc9932e04ca8
--- /dev/null
+++ b/llvm/test/Transforms/IndVarSimplify/pr51735-2.ll
@@ -0,0 +1,128 @@
+; RUN: opt -passes="loop(indvars)" \
+; RUN: --experimental-debuginfo-iterators=false -S -o - < %s | \
+; RUN: FileCheck --implicit-check-not="call void @llvm.dbg" \
+; RUN: --check-prefix=ALL-CHECK --check-prefix=PRE-CHECK %s
+; RUN: opt -passes="loop(indvars,loop-deletion)" \
+; RUN: --experimental-debuginfo-iterators=false -S -o - < %s | \
+; RUN: FileCheck --implicit-check-not="call void @llvm.dbg" \
+; RUN: --check-prefix=ALL-CHECK --check-prefix=POST-CHECK %s
+
+; Check what happens to a modified but otherwise unused variable in a loop
+; that gets deleted. The assignment in the loop is 'forgotten' by LLVM and
+; doesn't appear in the debugging information. This behaviour is suboptimal,
+; but we want to know if it changes
+
+; For all cases, LLDB shows
+; Var = <no location, value may have been optimized out>
+
+; 1 __attribute__((optnone)) int nop() {
+; 2 return 0;
+; 3 }
+; 4
+; 5 void bar() {
+; 6 int End = 777;
+; 7 int Index = 27;
+; 8 char Var = 1;
+; 9 for (; Index < End; ++Index) {
+; 10 if (Index == 666) {
+; 11 ++Var;
+; 12 }
+; 13 }
+; 14 nop();
+; 15 }
+
+; ALL-CHECK: entry:
+; ALL-CHECK: call void @llvm.dbg.value(metadata i32 1, metadata ![[DBG:[0-9]+]], {{.*}}
+
+; Only the 'indvars' pass is executed.
+; PRE-CHECK: for.cond:
+; PRE-CHECK: call void @llvm.dbg.value(metadata i32 %[[SSA_VAR_0:.+]], metadata ![[DBG]], {{.*}}
+; PRE-CHECK: call void @llvm.dbg.value(metadata !DIArgList{{.*}}
+
+; PRE-CHECK: for.body:
+; PRE-CHECK: {{.*}} = icmp eq i32 %[[SSA_INDEX_0:.+]], 666
+; PRE-CHECK: {{.*}} = add nsw i32 %[[SSA_VAR_0]], 1
+; PRE-CHECK: {{.*}} = select i1 {{.*}}, i32 {{.*}}, i32 %[[SSA_VAR_0]]
+; PRE-CHECK: call void @llvm.dbg.value(metadata i32 {{.*}}, metadata ![[DBG]], {{.*}}
+; PRE-CHECK: br label %for.cond
+
+; PRE-CHECK: for.end:
+; PRE-CHECK: ret void
+; PRE-CHECK-DAG: ![[DBG]] = !DILocalVariable(name: "Var"{{.*}})
+
+; The 'indvars' and 'loop-deletion' passes are executed.
+; POST-CHECK: for.end:
+; POST-CHECK: call void @llvm.dbg.value(metadata i32 undef, metadata ![[DBG:[0-9]+]], {{.*}}
+; POST-CHECK: ret void
+; POST-CHECK-DAG: ![[DBG]] = !DILocalVariable(name: "Var"{{.*}})
+
+define dso_local void @_Z3barv() local_unnamed_addr !dbg !18 {
+entry:
+ call void @llvm.dbg.value(metadata i32 1, metadata !24, metadata !DIExpression()), !dbg !22
+ br label %for.cond, !dbg !25
+
+for.cond: ; preds = %for.cond, %entry
+ %Index.0 = phi i32 [ 27, %entry ], [ %inc2, %for.body ], !dbg !22
+ %Var.0 = phi i32 [ 1, %entry ], [ %spec.select, %for.body ], !dbg !22
+ call void @llvm.dbg.value(metadata i32 %Var.0, metadata !24, metadata !DIExpression()), !dbg !22
+ %cmp = icmp ult i32 %Index.0, 777, !dbg !26
+ call void @llvm.dbg.value(metadata !DIArgList(i32 poison, i32 %Index.0), metadata !24, metadata !DIExpression(DW_OP_LLVM_arg, 0, DW_OP_LLVM_arg, 1, DW_OP_constu, 666, DW_OP_eq, DW_OP_LLVM_convert, 1, DW_ATE_unsigned, DW_OP_LLVM_convert, 32, DW_ATE_unsigned, DW_OP_plus, DW_OP_stack_value)), !dbg !22
+ %inc2 = add nuw nsw i32 %Index.0, 1, !dbg !29
+ br i1 %cmp, label %for.body, label %for.end, !dbg !30, !llvm.loop !31
+
+for.body: ; preds = %for.cond
+ %cmp1 = icmp eq i32 %Index.0, 666, !dbg !30
+ %inc = add nsw i32 %Var.0, 1
+ %spec.select = select i1 %cmp1, i32 %inc, i32 %Var.0, !dbg !32
+ call void @llvm.dbg.value(metadata i32 %spec.select, metadata !24, metadata !DIExpression()), !dbg !22
+ br label %for.cond, !dbg !34, !llvm.loop !35
+
+for.end: ; preds = %for.cond
+ ret void, !dbg !35
+}
+
+declare void @llvm.dbg.value(metadata, metadata, metadata)
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!2, !3, !4, !5, !6, !7, !8}
+!llvm.ident = !{!9}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus_14, file: !1, producer: "clang", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, splitDebugInlining: false, nameTableKind: None)
+!1 = !DIFile(filename: "test-b.cpp", directory: "")
+!2 = !{i32 7, !"Dwarf Version", i32 5}
+!3 = !{i32 2, !"Debug Info Version", i32 3}
+!4 = !{i32 1, !"wchar_size", i32 4}
+!5 = !{i32 8, !"PIC Level", i32 2}
+!6 = !{i32 7, !"PIE Level", i32 2}
+!7 = !{i32 7, !"uwtable", i32 2}
+!8 = !{i32 7, !"frame-pointer", i32 2}
+!9 = !{!"clang version 19.0.0"}
+!10 = distinct !DISubprogram(name: "nop", linkageName: "_Z3nopi", scope: !1, file: !1, line: 1, type: !11, scopeLine: 1, flags: DIFlagPrototyped, spFlags: DISPFlagDefinition, unit: !0, retainedNodes: !14)
+!11 = !DISubroutineType(types: !12)
+!12 = !{!13, !13}
+!13 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!14 = !{}
+!15 = !DILocalVariable(name: "Param", arg: 1, scope: !10, file: !1, line: 1, type: !13)
+!16 = !DILocation(line: 1, column: 38, scope: !10)
+!17 = !DILocation(line: 2, column: 3, scope: !10)
+!18 = distinct !DISubprogram(name: "bar", linkageName: "_Z3barv", scope: !1, file: !1, line: 5, type: !19, scopeLine: 5, flags: DIFlagPrototyped, spFlags: DISPFlagDefinition, unit: !0, retainedNodes: !14)
+!19 = !DISubroutineType(types: !20)
+!20 = !{null}
+!22 = !DILocation(line: 0, scope: !18)
+!24 = !DILocalVariable(name: "Var", scope: !18, file: !1, line: 8, type: !13)
+!25 = !DILocation(line: 9, column: 3, scope: !18)
+!26 = !DILocation(line: 9, column: 16, scope: !27)
+!27 = distinct !DILexicalBlock(scope: !28, file: !1, line: 9, column: 3)
+!28 = distinct !DILexicalBlock(scope: !18, file: !1, line: 9, column: 3)
+!29 = !DILocation(line: 9, column: 23, scope: !27)
+!30 = !DILocation(line: 9, column: 3, scope: !28)
+!31 = distinct !{!31, !30, !32, !33}
+!32 = !DILocation(line: 11, column: 9, scope: !28)
+!33 = !{!"llvm.loop.mustprogress"}
+!34 = !DILocation(line: 12, column: 3, scope: !18)
+!35 = !DILocation(line: 13, column: 1, scope: !18)
+!36 = distinct !DISubprogram(name: "main", scope: !1, file: !1, line: 15, type: !37, scopeLine: 15, flags: DIFlagPrototyped, spFlags: DISPFlagDefinition, unit: !0)
+!37 = !DISubroutineType(types: !38)
+!38 = !{!13}
+!39 = !DILocation(line: 16, column: 3, scope: !36)
+!40 = !DILocation(line: 17, column: 1, scope: !36)
diff --git a/llvm/test/Transforms/IndVarSimplify/pr51735-3.ll b/llvm/test/Transforms/IndVarSimplify/pr51735-3.ll
new file mode 100644
index 00000000000000..ac9964743e0ffc
--- /dev/null
+++ b/llvm/test/Transforms/IndVarSimplify/pr51735-3.ll
@@ -0,0 +1,131 @@
+; RUN: opt -passes="loop(indvars)" \
+; RUN: --experimental-debuginfo-iterators=false -S -o - < %s | \
+; RUN: FileCheck --implicit-check-not="call void @llvm.dbg" \
+; RUN: --check-prefix=ALL-CHECK --check-prefix=PRE-CHECK %s
+; RUN: opt -passes="loop(indvars,loop-deletion)" \
+; RUN: --experimental-debuginfo-iterators=false -S -o - < %s | \
+; RUN: FileCheck --implicit-check-not="call void @llvm.dbg" \
+; RUN: --check-prefix=ALL-CHECK --check-prefix=POST-CHECK %s
+
+; Check what happens to a modified but otherwise unused variable in a loop
+; that gets deleted. The assignment in the loop is 'forgotten' by LLVM and
+; doesn't appear in the debugging information. This behaviour is suboptimal,
+; but we want to know if it changes
+
+; For all cases, LLDB shows
+; Var = <no location, value may have been optimized out>
+
+; 1 __attribute__((optnone)) int nop() {
+; 2 return 0;
+; 3 }
+; 4
+; 5 void bar() {
+; 6 int End = 777;
+; 7 int Index = 27;
+; 8 char Var = 1;
+; 9 for (; Index < End; ++Index) {
+; 10 if (Index == 666) {
+; 11 Var = 555;
+; 12 }
+; 13 }
+; 14 nop();
+; 15 }
+
+; ALL-CHECK: entry:
+; ALL-CHECK: call void @llvm.dbg.value(metadata i32 1, metadata ![[DBG:[0-9]+]], {{.*}}
+
+; Only the 'indvars' pass is executed.
+; PRE-CHECK: if.then:
+; PRE-CHECK: call void @llvm.dbg.value(metadata i32 555, metadata ![[DBG]], {{.*}}
+
+; PRE-CHECK: for.inc:
+; PRE-CHECK: %[[SSA_VAR_0:.+]] = phi i32 [ 1, %for.body ], [ 555, %if.then ]
+; PRE-CHECK: call void @llvm.dbg.value(metadata i32 %[[SSA_VAR_0]], metadata ![[DBG]], {{.*}}
+; PRE-CHECK: {{.*}} = add nuw nsw i32 %[[SSA_INDEX_0:.+]], 1
+; PRE-CHECK: br label %for.cond
+
+; PRE-CHECK: for.end:
+; PRE-CHECK: ret void
+; PRE-CHECK-DAG: ![[DBG]] = !DILocalVariable(name: "Var"{{.*}})
+
+; The 'indvars' and 'loop-deletion' passes are executed.
+; POST-CHECK: for.end:
+; POST-CHECK: call void @llvm.dbg.value(metadata i32 555, metadata ![[DBG]], {{.*}}
+; POST-CHECK: ret void
+; POST-CHECK-DAG: ![[DBG]] = !DILocalVariable(name: "Var"{{.*}})
+
+define dso_local void @_Z3barv() local_unnamed_addr !dbg !18 {
+entry:
+ call void @llvm.dbg.value(metadata i32 1, metadata !24, metadata !DIExpression()), !dbg !22
+ br label %for.cond, !dbg !25
+
+for.cond: ; preds = %for.inc, %entry
+ %Index.0 = phi i32 [ 27, %entry ], [ %inc, %for.inc ], !dbg !22
+ %cmp = icmp ult i32 %Index.0, 777, !dbg !26
+ br i1 %cmp, label %for.body, label %for.end, !dbg !30, !llvm.loop !29
+
+for.body: ; preds = %for.cond
+ %cmp1 = icmp eq i32 %Index.0, 666, !dbg !30
+ br i1 %cmp1, label %if.then, label %for.inc, !dbg !32
+
+if.then: ; preds = %for.body
+ call void @llvm.dbg.value(metadata i32 555, metadata !24, metadata !DIExpression()), !dbg !22
+ br label %for.inc, !dbg !34, !llvm.loop !32
+
+for.inc: ; preds = %for.body, %if.then
+ %Var.0 = phi i32 [ 1, %for.body ], [ 555, %if.then ], !dbg !22
+ call void @llvm.dbg.value(metadata i32 %Var.0, metadata !24, metadata !DIExpression()), !dbg !22
+ %inc = add nuw nsw i32 %Index.0, 1, !dbg !29
+ br label %for.cond, !dbg !34, !llvm.loop !35
+
+for.end: ; preds = %for.cond
+ ret void, !dbg !35
+}
+
+declare void @llvm.dbg.value(metadata, metadata, metadata)
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!2, !3, !4, !5, !6, !7, !8}
+!llvm.ident = !{!9}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus_14, file: !1, producer: "clang", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, splitDebugInlining: false, nameTableKind: None)
+!1 = !DIFile(filename: "test-c.cpp", directory: "")
+!2 = !{i32 7, !"Dwarf Version", i32 5}
+!3 = !{i32 2, !"Debug Info Version", i32 3}
+!4 = !{i32 1, !"wchar_size", i32 4}
+!5 = !{i32 8, !"PIC Level", i32 2}
+!6 = !{i32 7, !"PIE Level", i32 2}
+!7 = !{i32 7, !"uwtable", i32 2}
+!8 = !{i32 7, !"frame-pointer", i32 2}
+!9 = !{!"clang version 19.0.0"}
+!10 = distinct !DISubprogram(name: "nop", linkageName: "_Z3nopi", scope: !1, file: !1, line: 1, type: !11, scopeLine: 1, flags: DIFlagPrototyped, spFlags: DISPFlagDefinition, unit: !0, retainedNodes: !14)
+!11 = !DISubroutineType(types: !12)
+!12 = !{!13, !13}
+!13 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!14 = !{}
+!15 = !DILocalVariable(name: "Param", arg: 1, scope: !10, file: !1, line: 1, type: !13)
+!16 = !DILocation(line: 1, column: 38, scope: !10)
+!17 = !DILocation(line: 2, column: 3, scope: !10)
+!18 = distinct !DISubprogram(name: "bar", linkageName: "_Z3barv", scope: !1, file: !1, line: 5, type: !19, scopeLine: 5, flags: DIFlagPrototyped, spFlags: DISPFlagDefinition, unit: !0, retainedNodes: !14)
+!19 = !DISubroutineType(types: !20)
+!20 = !{null}
+!21 = !DILocalVariable(name: "End", scope: !18, file: !1, line: 6, type: !13)
+!22 = !DILocation(line: 0, scope: !18)
+!23 = !DILocalVariable(name: "Index", scope: !18, file: !1, line: 7, type: !13)
+!24 = !DILocalVariable(name: "Var", scope: !18, file: !1, line: 8, type: !13)
+!25 = !DILocation(line: 9, column: 3, scope: !18)
+!26 = !DILocation(line: 9, column: 16, scope: !27)
+!27 = distinct !DILexicalBlock(scope: !28, file: !1, line: 9, column: 3)
+!28 = distinct !DILexicalBlock(scope: !18, file: !1, line: 9, column: 3)
+!29 = !DILocation(line: 9, column: 23, scope: !27)
+!30 = !DILocation(line: 9, column: 3, scope: !28)
+!31 = distinct !{!31, !30, !32, !33}
+!32 = !DILocation(line: 11, column: 13, scope: !28)
+!33 = !{!"llvm.loop.mustprogress"}
+!34 = !DILocation(line: 12, column: 3, scope: !18)
+!35 = !DILocation(line: 13, column: 1, scope: !18)
+!36 = distinct !DISubprogram(name: "main", scope: !1, file: !1, line: 15, type: !37, scopeLine: 15, flags: DIFlagPrototyped, spFlags: DISPFlagDefinition, unit: !0)
+!37 = !DISubroutineType(types: !38)
+!38 = !{!13}
+!39 = !DILocation(line: 16, column: 3, scope: !36)
+!40 = !DILocation(line: 17, column: 1, scope: !36)
diff --git a/llvm/test/Transforms/IndVarSimplify/pr51735.ll b/llvm/test/Transforms/IndVarSimplify/pr51735.ll
new file mode 100644
index 00000000000000..3014b3467852d1
--- /dev/null
+++ b/llvm/test/Transforms/IndVarSimplify/pr51735.ll
@@ -0,0 +1,104 @@
+; RUN: opt -passes="loop(indvars)" \
+; RUN: --experimental-debuginfo-iterators=false -S -o - < %s | \
+; RUN: FileCheck --check-prefix=PRE-CHECK %s
+; RUN: opt -passes="loop(indvars,loop-deletion)" \
+; RUN: --experimental-debuginfo-iterators=false -S -o - < %s | \
+; RUN: FileCheck --check-prefix=POST-CHECK %s
+
+; Make sure that when we delete the loop in the code below, that the variable
+; Index has the 777 value.
+
+; 1 __attribute__((optnone)) int nop() {
+; 2 return 0;
+; 3 }
+; 4
+; 5 void bar() {
+; 6 int End = 777;
+; 7 int Index = 27;
+; 8 char Var = 1;
+; 9 for (; Index < End; ++Index)
+; 10 ;
+; 11 nop();
+; 12 }
+; 13
+; 14 int main () {
+; 15 bar();
+; 16 }
+
+; Only the 'indvars' pass is executed.
+; As this test case does not fire the 'indvars' transformation, no debug values
+; are preserved and or added.
+
+; PRE-CHECK: for.cond:
+; PRE-CHECK: call void @llvm.dbg.value(metadata i32 poison, metadata ![[DBG_1:[0-9]+]], {{.*}}
+; PRE-CHECK: call void @llvm.dbg.value(metadata i32 poison, metadata ![[DBG_1]], {{.*}}
+; PRE-CHECK: br i1 false, label %for.cond, label %for.end
+
+; PRE-CHECK: for.end:
+; PRE-CHECK-NOT: call void @llvm.dbg.value
+; PRE-CHECK: ret void
+; PRE-CHECK-DAG: ![[DBG_1]] = !DILocalVariable(name: "Index"{{.*}})
+
+; The 'indvars' and 'loop-deletion' passes are executed.
+; The loop is deleted and the debug values collected by 'indvars' are used by
+; 'loop-deletion' to add the induction variable debug value.
+
+; POST-CHECK: for.end:
+; POST-CHECK: call void @llvm.dbg.value(metadata i32 777, metadata ![[DBG_2:[0-9]+]], {{.*}}
+; POST-CHECK: ret void
+; POST-CHECK-DAG: ![[DBG_2]] = !DILocalVariable(name: "Index"{{.*}})
+
+define dso_local void @_Z3barv() local_unnamed_addr #1 !dbg !15 {
+entry:
+ call void @llvm.dbg.value(metadata i32 777, metadata !19, metadata !DIExpression()), !dbg !20
+ call void @llvm.dbg.value(metadata i32 27, metadata !21, metadata !DIExpression()), !dbg !20
+ call void @llvm.dbg.value(metadata i32 1, metadata !22, metadata !DIExpression()), !dbg !20
+ br label %for.cond, !dbg !23
+
+for.cond: ; preds = %for.cond, %entry
+ %Index.0 = phi i32 [ 27, %entry ], [ %inc, %for.cond ], !dbg !20
+ call void @llvm.dbg.value(metadata i32 %Index.0, metadata !21, metadata !DIExpression()), !dbg !20
+ %cmp = icmp ult i32 %Index.0, 777, !dbg !24
+ %inc = add nuw nsw i32 %Index.0, 1, !dbg !27
+ call void @llvm.dbg.value(metadata i32 %inc, metadata !21, metadata !DIExpression()), !dbg !20
+ br i1 %cmp, label %for.cond, label %for.end, !dbg !28, !llvm.loop !29
+
+for.end: ; preds = %for.cond
+ ret void, !dbg !33
+}
+
+declare void @llvm.dbg.value(metadata, metadata, metadata)
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!2, !3, !4, !5, !6, !7, !8}
+!llvm.ident = !{!9}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus_14, file: !1, producer: "clang", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, splitDebugInlining: false, nameTableKind: None)
+!1 = !DIFile(filename: "test.cpp", directory: "")
+!2 = !{i32 7, !"Dwarf Version", i32 5}
+!3 = !{i32 2, !"Debug Info Version", i32 3}
+!4 = !{i32 1, !"wchar_size", i32 4}
+!5 = !{i32 8, !"PIC Level", i32 2}
+!6 = !{i32 7, !"PIE Level", i32 2}
+!7 = !{i32 7, !"uwtable", i32 2}
+!8 = !{i32 7, !"frame-pointer", i32 2}
+!9 = !{!"clang version 18.0.0"}
+!13 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!15 = distinct !DISubprogram(name: "bar", linkageName: "_Z3barv", scope: !1, file: !1, line: 5, type: !16, scopeLine: 5, flags: DIFlagPrototyped, spFlags: DISPFlagDefinition, unit: !0, retainedNodes: !18)
+!16 = !DISubroutineType(types: !17)
+!17 = !{null}
+!18 = !{}
+!19 = !DILocalVariable(name: "End", scope: !15, file: !1, line: 6, type: !13)
+!20 = !DILocation(line: 0, scope: !15)
+!21 = !DILocalVariable(name: "Index", scope: !15, file: !1, line: 7, type: !13)
+!22 = !DILocalVariable(name: "Var", scope: !15, file: !1, line: 8, type: !13)
+!23 = !DILocation(line: 9, column: 3, scope: !15)
+!24 = !DILocation(line: 9, column: 16, scope: !25)
+!25 = distinct !DILexicalBlock(scope: !26, file: !1, line: 9, column: 3)
+!26 = distinct !DILexicalBlock(scope: !15, file: !1, line: 9, column: 3)
+!27 = !DILocation(line: 9, column: 23, scope: !25)
+!28 = !DILocation(line: 9, column: 3, scope: !26)
+!29 = distinct !{!29, !28, !30, !31}
+!30 = !DILocation(line: 10, column: 5, scope: !26)
+!31 = !{!"llvm.loop.mustprogress"}
+!33 = !DILocation(line: 12, column: 1, scope: !15)
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