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Improve the effectiveness of ADCE's debug info salvaging 

This patch improves the effectiveness of ADCE's debug info salvaging
by processing the instructions in reverse order and delaying
dropAllReferences until after debug info salvaging. This allows
salvaging of entire chains of deleted instructions!

Previously we would remove all references from an instruction, which
would make it impossible to use that instruction to salvage a later
instruction in the instruction stream, because its operands were
already removed.

Differential Revision: https://reviews.llvm.org/D110462
This commit is contained in:
Adrian Prantl 2021-09-24 17:16:59 -07:00
parent 1b998a5f0c
commit 9637b045e6
2 changed files with 8 additions and 4 deletions
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6
llvm/lib/Transforms/Scalar/ADCE.cpp
View File

@ -538,7 +538,7 @@ bool AggressiveDeadCodeElimination::removeDeadInstructions() {
// that have no side effects and do not influence the control flow or return
// value of the function, and may therefore be deleted safely.
// NOTE: We reuse the Worklist vector here for memory efficiency.
for (Instruction &I : instructions(F)) {
for (Instruction &I : llvm::reverse(instructions(F))) {
// Check if the instruction is alive.
if (isLive(&I))
continue;
@ -554,9 +554,11 @@ bool AggressiveDeadCodeElimination::removeDeadInstructions() {
// Prepare to delete.
Worklist.push_back(&I);
salvageDebugInfo(I);
I.dropAllReferences();
}
for (Instruction *&I : Worklist)
I->dropAllReferences();
for (Instruction *&I : Worklist) {
++NumRemoved;
I->eraseFromParent();

6
llvm/test/Transforms/Util/salvage-debuginfo.ll
View File

@ -5,8 +5,10 @@ define void @f(i32) !dbg !8 {
entry:
%p_x = inttoptr i32 %0 to i8*
%i_x = ptrtoint i8* %p_x to i32
; CHECK: call void @llvm.dbg.value(metadata i8* undef,
; CHECK-SAME: !DIExpression(DW_OP_LLVM_convert, 64, DW_ATE_unsigned,
; CHECK: call void @llvm.dbg.value(metadata i32 %0,
; CHECK-SAME: !DIExpression(DW_OP_LLVM_convert, 32, DW_ATE_unsigned,
; CHECK-SAME: DW_OP_LLVM_convert, 64, DW_ATE_unsigned,
; CHECK-SAME: DW_OP_LLVM_convert, 64, DW_ATE_unsigned,
; CHECK-SAME: DW_OP_LLVM_convert, 32, DW_ATE_unsigned, DW_OP_stack_value))
call void @llvm.dbg.value(metadata i32 %i_x, metadata !11, metadata !DIExpression()), !dbg !13
ret void, !dbg !13