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Improve the effectiveness of BDCE's debug info salvaging

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This patch improves the effectiveness of BDCE'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.

This reapplies the previous patch with a fix for a use-after-free.

Differential Revision: https://reviews.llvm.org/D110568
This commit is contained in:
Adrian Prantl 2021-09-27 10:51:04 -07:00
parent 981b12fe89
commit 9232ca4712
2 changed files with 6 additions and 2 deletions
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7
llvm/lib/Transforms/Scalar/BDCE.cpp
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@ -106,9 +106,7 @@ static bool bitTrackingDCE(Function &F, DemandedBits &DB) {
(I.getType()->isIntOrIntVectorTy() &&
DB.getDemandedBits(&I).isNullValue() &&
wouldInstructionBeTriviallyDead(&I))) {
salvageDebugInfo(I);
Worklist.push_back(&I);
I.dropAllReferences();
Changed = true;
continue;
}
@ -155,6 +153,11 @@ static bool bitTrackingDCE(Function &F, DemandedBits &DB) {
}
}
for (Instruction *&I : llvm::reverse(Worklist)) {
salvageDebugInfo(*I);
I->dropAllReferences();
}
for (Instruction *&I : Worklist) {
++NumRemoved;
I->eraseFromParent();

1
llvm/test/Transforms/Util/salvage-debuginfo.ll
View file

@ -1,4 +1,5 @@
; RUN: opt -adce %s -S -o - | FileCheck %s
; RUN: opt -bdce %s -S -o - | FileCheck %s
target datalayout = "e-m:o-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
target triple = "x86_64-apple-macosx"
define void @f(i32) !dbg !8 {