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[InstCombine] Avoid redundant or out-of-order debug value sinking

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This patch modifies TryToSinkInstruction in the InstCombine pass, to prevent
redundant debug intrinsics from being produced, and also prevent the intrinsics
from being emitted in an incorrect order. It does this by ensuring that when
this pass sinks an instruction and creates clones of the debug intrinsics that
use that instruction, it inserts those debug intrinsics in their original order,
and only inserts the last debug intrinsic for each variable in the Instruction's
block.

Differential revision: https://reviews.llvm.org/D95463
This commit is contained in:
Stephen Tozer 2021-02-26 13:04:33 +00:00
parent 7d20cd7bf1
commit abe864fcc4
3 changed files with 53 additions and 4 deletions
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24
lib/Transforms/InstCombine/InstructionCombining.cpp
View File

@ -3577,6 +3577,14 @@ static bool TryToSinkInstruction(Instruction *I, BasicBlock *DestBlock) {
// here, but that computation has been sunk.
SmallVector<DbgVariableIntrinsic *, 2> DbgUsers;
findDbgUsers(DbgUsers, I);
// Process the sinking DbgUsers in reverse order, as we only want to clone the
// last appearing debug intrinsic for each given variable.
SmallVector<DbgVariableIntrinsic *, 2> DbgUsersToSink;
for (DbgVariableIntrinsic *DVI : DbgUsers)
if (DVI->getParent() == SrcBlock)
DbgUsersToSink.push_back(DVI);
llvm::sort(DbgUsersToSink,
[](auto *A, auto *B) { return B->comesBefore(A); });
// Update the arguments of a dbg.declare instruction, so that it
// does not point into a sunk instruction.
@ -3592,12 +3600,20 @@ static bool TryToSinkInstruction(Instruction *I, BasicBlock *DestBlock) {
};
SmallVector<DbgVariableIntrinsic *, 2> DIIClones;
for (auto User : DbgUsers) {
SmallSet<DebugVariable, 4> SunkVariables;
for (auto User : DbgUsersToSink) {
// A dbg.declare instruction should not be cloned, since there can only be
// one per variable fragment. It should be left in the original place
// because the sunk instruction is not an alloca (otherwise we could not be
// here).
if (User->getParent() != SrcBlock || updateDbgDeclare(User))
if (updateDbgDeclare(User))
continue;
DebugVariable DbgUserVariable =
DebugVariable(User->getVariable(), User->getExpression(),
User->getDebugLoc()->getInlinedAt());
if (!SunkVariables.insert(DbgUserVariable).second)
continue;
DIIClones.emplace_back(cast<DbgVariableIntrinsic>(User->clone()));
@ -3607,7 +3623,9 @@ static bool TryToSinkInstruction(Instruction *I, BasicBlock *DestBlock) {
// Perform salvaging without the clones, then sink the clones.
if (!DIIClones.empty()) {
salvageDebugInfoForDbgValues(*I, DbgUsers);
for (auto &DIIClone : DIIClones) {
// The clones are in reverse order of original appearance, reverse again to
// maintain the original order.
for (auto &DIIClone : llvm::reverse(DIIClones)) {
DIIClone->insertBefore(&*InsertPos);
LLVM_DEBUG(dbgs() << "SINK: " << *DIIClone << '\n');
}

31
test/Transforms/InstCombine/debuginfo-sink.ll
View File

@ -52,6 +52,33 @@ sink2:
ret i32 %0
}
; This GEP is sunk, and has multiple debug uses in the same block. Check that
; only the last use is cloned into the sunk block, and that both of the
; original dbg.values are salvaged.
;
; CHECK-LABEL: define i32 @baz(i32*
; CHECK: call void @llvm.dbg.value(metadata i32* %a, metadata !{{[0-9]+}},
; CHECK-SAME: metadata !DIExpression(DW_OP_plus_uconst, 4, DW_OP_stack_value))
; CHECK-NEXT: call void @llvm.dbg.value(metadata i32* %a, metadata !{{[0-9]+}},
; CHECK-SAME: metadata !DIExpression(DW_OP_plus_uconst, 4, DW_OP_plus_uconst, 5, DW_OP_stack_value))
; CHECK-NEXT: br label %sink1
define i32 @baz(i32 *%a) !dbg !80 {
entry:
%gep = getelementptr i32, i32 *%a, i32 1
call void @llvm.dbg.value(metadata i32 *%gep, metadata !83, metadata !12), !dbg !84
call void @llvm.dbg.value(metadata i32 *%gep, metadata !83, metadata !DIExpression(DW_OP_plus_uconst, 5)), !dbg !85
br label %sink1
sink1:
; CHECK-LABEL: sink1:
; CHECK: call void @llvm.dbg.value(metadata i32* %gep,
; CHECK-SAME: metadata !{{[0-9]+}}, metadata !DIExpression(DW_OP_plus_uconst, 5))
; CHECK-NEXT: load
%0 = load i32, i32* %gep, align 4, !dbg !85
ret i32 %0, !dbg !85
}
!llvm.dbg.cu = !{!0}
!llvm.module.flags = !{!3, !4, !5}
!llvm.ident = !{!6}
@ -76,3 +103,7 @@ sink2:
!72 = !{!10, !10, !10}
!73 = !DILocalVariable(name: "k", scope: !70, file: !1, line: 2, type: !10)
!74 = !DILocation(line: 5, column: 3, scope: !70)
!80 = distinct !DISubprogram(name: "baz", scope: !1, file: !1, line: 2, type: !8, isLocal: false, isDefinition: true, scopeLine: 3, flags: DIFlagPrototyped, isOptimized: false, unit: !0, retainedNodes: !2)
!83 = !DILocalVariable(name: "l", scope: !80, file: !1, line: 2, type: !10)
!84 = !DILocation(line: 5, column: 3, scope: !80)
!85 = !DILocation(line: 6, column: 3, scope: !80)

2
test/Transforms/InstCombine/debuginfo_add.ll
View File

@ -36,8 +36,8 @@ for.body.lr.ph: ; preds = %entry
; The add is later eliminated, so we verify that the dbg.value is salvaged by using DW_OP_minus.
; CHECK-LABEL: for.body.lr.ph:
; CHECK-NEXT: %0 = load
; CHECK-NEXT: call void @llvm.dbg.value(metadata i64 %0, metadata !26, metadata !DIExpression(DW_OP_constu, 4096, DW_OP_minus, DW_OP_stack_value)), !dbg !
; CHECK-NEXT: call void @llvm.dbg.value(metadata i64 %0, metadata !25, metadata !DIExpression()), !dbg !
; CHECK-NEXT: call void @llvm.dbg.value(metadata i64 %0, metadata !26, metadata !DIExpression(DW_OP_constu, 4096, DW_OP_minus, DW_OP_stack_value)), !dbg !
br label %for.body, !dbg !32
for.body: ; preds = %for.body.lr.ph, %for.body