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[InstCombine] weaken assertions for icmp folds (PR35846)

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Because of potential UB (known bits conflicts with an llvm.assume),
we have to check rather than assert here because InstSimplify doesn't
kill the compare:
https://bugs.llvm.org/show_bug.cgi?id=35846

llvm-svn: 322104
This commit is contained in:
Sanjay Patel 2018-01-09 18:56:03 +00:00
parent 09464eb2ae
commit 883f134b81
2 changed files with 21 additions and 10 deletions
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14
lib/Transforms/InstCombine/InstCombineCompares.cpp
View File

@ -1893,11 +1893,8 @@ Instruction *InstCombiner::foldICmpShlConstant(ICmpInst &Cmp,
APInt ShiftedC = C.ashr(*ShiftAmt);
return new ICmpInst(Pred, X, ConstantInt::get(ShType, ShiftedC));
}
if (Pred == ICmpInst::ICMP_EQ || Pred == ICmpInst::ICMP_NE) {
// This is the same code as the SGT case, but assert the pre-condition
// that is needed for this to work with equality predicates.
assert(C.ashr(*ShiftAmt).shl(*ShiftAmt) == C &&
"Compare known true or false was not folded");
if ((Pred == ICmpInst::ICMP_EQ || Pred == ICmpInst::ICMP_NE) &&
C.ashr(*ShiftAmt).shl(*ShiftAmt) == C) {
APInt ShiftedC = C.ashr(*ShiftAmt);
return new ICmpInst(Pred, X, ConstantInt::get(ShType, ShiftedC));
}
@ -1926,11 +1923,8 @@ Instruction *InstCombiner::foldICmpShlConstant(ICmpInst &Cmp,
APInt ShiftedC = C.lshr(*ShiftAmt);
return new ICmpInst(Pred, X, ConstantInt::get(ShType, ShiftedC));
}
if (Pred == ICmpInst::ICMP_EQ || Pred == ICmpInst::ICMP_NE) {
// This is the same code as the UGT case, but assert the pre-condition
// that is needed for this to work with equality predicates.
assert(C.lshr(*ShiftAmt).shl(*ShiftAmt) == C &&
"Compare known true or false was not folded");
if ((Pred == ICmpInst::ICMP_EQ || Pred == ICmpInst::ICMP_NE) &&
C.lshr(*ShiftAmt).shl(*ShiftAmt) == C) {
APInt ShiftedC = C.lshr(*ShiftAmt);
return new ICmpInst(Pred, X, ConstantInt::get(ShType, ShiftedC));
}

17
test/Transforms/InstCombine/assume.ll
View File

@ -275,6 +275,23 @@ define i1 @nonnull4(i32** %a) {
ret i1 %rval
}
; PR35846 - https://bugs.llvm.org/show_bug.cgi?id=35846
define i32 @assumption_conflicts_with_known_bits(i32 %a, i32 %b) {
; CHECK-LABEL: @assumption_conflicts_with_known_bits(
; CHECK-NEXT: tail call void @llvm.assume(i1 false)
; CHECK-NEXT: ret i32 0
;
%and1 = and i32 %b, 3
%B1 = lshr i32 %and1, %and1
%B3 = shl nuw nsw i32 %and1, %B1
%cmp = icmp eq i32 %B3, 1
tail call void @llvm.assume(i1 %cmp)
%cmp2 = icmp eq i32 %B1, %B3
tail call void @llvm.assume(i1 %cmp2)
ret i32 %and1
}
attributes #0 = { nounwind uwtable }
attributes #1 = { nounwind }