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[NaryReassociate] Detect deleted instr with WeakVH 

Summary:
If NaryReassociate succeed it will, when replacing the old instruction
with the new instruction, also recursively delete trivially
dead instructions from the old instruction. However, if the input to the
NaryReassociate pass contain dead code it is not save to recursively
delete trivially deadinstructions as it might lead to deleting the newly
created instruction.

This patch will fix the problem by using WeakVH to detect this
rare case, when the newly created instruction is dead, and it will then
restart the basic block iteration from the beginning.

This fixes pr37539

Reviewers: tra, meheff, grosser, sanjoy

Reviewed By: sanjoy

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D47139

llvm-svn: 333155
This commit is contained in:
Karl-Johan Karlsson 2018-05-24 06:09:02 +00:00
parent c27ad9bbc8
commit 478232d52f
2 changed files with 39 additions and 3 deletions
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13
llvm/lib/Transforms/Scalar/NaryReassociate.cpp
View File

@ -240,10 +240,17 @@ bool NaryReassociatePass::doOneIteration(Function &F) {
Changed = true;
SE->forgetValue(&*I);
I->replaceAllUsesWith(NewI);
// If SeenExprs constains I's WeakTrackingVH, that entry will be
// replaced with
// nullptr.
WeakVH NewIExist = NewI;
// If SeenExprs/NewIExist contains I's WeakTrackingVH/WeakVH, that
// entry will be replaced with nullptr if deleted.
RecursivelyDeleteTriviallyDeadInstructions(&*I, TLI);
if (!NewIExist) {
// Rare occation where the new instruction (NewI) have been removed,
// probably due to parts of the input code was dead from the
// beginning, reset the iterator and start over from the beginning
I = BB->begin();
continue;
}
I = NewI->getIterator();
}
// Add the rewritten instruction to SeenExprs; the original instruction

29
llvm/test/Transforms/NaryReassociate/pr37539.ll Normal file
View File

@ -0,0 +1,29 @@
; RUN: opt < %s -nary-reassociate -S -o - | FileCheck %s
; The test check that compilation does not segv (see pr37539).
define void @f1() {
; CHECK-LABEL: @f1(
; CHECK-NEXT: br label %[[BB1:.*]]
; CHECK: [[BB1]]
; CHECK-NEXT: [[P1:%.*]] = phi i16 [ 0, [[TMP0:%.*]] ], [ [[A1:%.*]], %[[BB1]] ]
; CHECK-NEXT: [[SCEVGEP_OFFS:%.*]] = add i16 2, 0
; CHECK-NEXT: [[A1]] = add i16 [[P1]], [[SCEVGEP_OFFS]]
; CHECK-NEXT: br i1 false, label %[[BB1]], label %[[BB7:.*]]
; CHECK: [[BB7]]
; CHECK-NEXT: ret void
;
br label %bb1
bb1:
%p1 = phi i16 [ 0, %0 ], [ %a1, %bb1 ]
%p2 = phi i16 [ 0, %0 ], [ %a2, %bb1 ]
%scevgep.offs = add i16 2, 0
%a1 = add i16 %p1, %scevgep.offs
%scevgep.offs5 = add i16 2, 0
%a2 = add i16 %p2, %scevgep.offs5
br i1 false, label %bb1, label %bb7
bb7:
ret void
}