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[InstCombine] Avoid iteration/mutation conflict 

Summary:
When iterating users of a multiply in processUMulZExtIdiom, the
call to setOperand in the truncation case may replace the use
being visited; make sure the iterator has been advanced before
doing that replacement.

Reviewers: majnemer, davide

Reviewed By: davide

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D48192

llvm-svn: 334844
This commit is contained in:
Joseph Tremoulet 2018-06-15 16:52:40 +00:00
parent 4adf24502e
commit 6f406d4f02
2 changed files with 40 additions and 1 deletions
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3
llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
View File

@ -3849,7 +3849,8 @@ static Instruction *processUMulZExtIdiom(ICmpInst &I, Value *MulVal,
// mul.with.overflow and adjust properly mask/size.
if (MulVal->hasNUsesOrMore(2)) {
Value *Mul = Builder.CreateExtractValue(Call, 0, "umul.value");
for (User *U : MulVal->users()) {
for (auto UI = MulVal->user_begin(), UE = MulVal->user_end(); UI != UE;) {
User *U = *UI++;
if (U == &I || U == OtherVal)
continue;
if (TruncInst *TI = dyn_cast<TruncInst>(U)) {

38
llvm/test/Transforms/InstCombine/icmp-mul-zext.ll
View File

@ -80,3 +80,41 @@ if.then9:
ret void
}
; Repro case for bug involving mutating a list while
; iterating it.
declare i16 @aux(i8)
define i16 @iter_breaker(i16 %a, i16 %b) {
; CHECK-LABEL: @iter_breaker(
; CHECK-NEXT: [[UMUL:%.*]] = call { i16, i1 } @llvm.umul.with.overflow.i16(i16 [[A:%.*]], i16 [[B:%.*]])
; CHECK-NEXT: [[UMUL_VALUE:%.*]] = extractvalue { i16, i1 } [[UMUL]], 0
; CHECK-NEXT: [[DID_OVF:%.*]] = extractvalue { i16, i1 } [[UMUL]], 1
; CHECK-NEXT: br i1 [[DID_OVF]], label [[RET1:%.*]], label [[RET2:%.*]]
; CHECK: ret1:
; CHECK-NEXT: [[TRUNC_REMAIN:%.*]] = trunc i16 [[UMUL_VALUE]] to i8
; CHECK-NEXT: [[VAL:%.*]] = call i16 @aux(i8 [[TRUNC_REMAIN]])
; CHECK-NEXT: ret i16 [[VAL]]
; CHECK: ret2:
; CHECK-NEXT: ret i16 [[UMUL_VALUE]]
;
%a_wide = zext i16 %a to i32
%b_wide = zext i16 %b to i32
%mul_wide = mul i32 %a_wide, %b_wide ; uses of %mul_wide will be iterated
%trunc_remain = trunc i32 %mul_wide to i8 ; this use will be replaced w/ new value
; when iteration visits it, switching
; iteration to the uses of new value
%trunc_unnecessary = trunc i32 %mul_wide to i16 ; uses of %trunc_unnecessary will have
; been updated to uses of new value
%did_ovf = icmp ugt i32 %mul_wide, 65535
br i1 %did_ovf, label %ret1, label %ret2
ret1:
%val = call i16 @aux(i8 %trunc_remain)
ret i16 %val
ret2:
ret i16 %trunc_unnecessary ; crash visiting this use after corrupting iterator
}