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[IR] fix crash in Constant::isElementWiseEqual() with FP types

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We lifted this code from InstCombine for general usage in:
rL369842
...but it's not safe as-is. There are no existing users that can
trigger this bug, but I discovered it via crashing several
regression tests when trying to use it for select folding in
InstSimplify.

ICmp requires (vector) integer types, so give up on anything that's
not integer or FP (pointers and ?) then bitcast the constants
before trying the match. That matches the definition of "equal or
undef" that I was looking for. If someone wants an FP-aware version
of equality (deal with NaN, -0.0), that could be a different mode
or different function.

Differential Revision: https://reviews.llvm.org/D72784
This commit is contained in:
Sanjay Patel 2020-01-16 16:20:48 -05:00
parent 3c615417b5
commit bc125ae78b
2 changed files with 25 additions and 8 deletions
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15
lib/IR/Constants.cpp
View File

@ -286,12 +286,17 @@ bool Constant::isElementWiseEqual(Value *Y) const {
if (!isa<Constant>(Y) || !Ty->isVectorTy() || Ty != Y->getType())
return false;
// TODO: Compare pointer constants?
if (!(Ty->getVectorElementType()->isIntegerTy() ||
Ty->getVectorElementType()->isFloatingPointTy()))
return false;
// They may still be identical element-wise (if they have `undef`s).
// FIXME: This crashes on FP vector constants.
return match(ConstantExpr::getICmp(ICmpInst::Predicate::ICMP_EQ,
const_cast<Constant *>(this),
cast<Constant>(Y)),
m_One());
// Bitcast to integer to allow exact bitwise comparison for all types.
Type *IntTy = VectorType::getInteger(cast<VectorType>(Ty));
Constant *C0 = ConstantExpr::getBitCast(const_cast<Constant *>(this), IntTy);
Constant *C1 = ConstantExpr::getBitCast(cast<Constant>(Y), IntTy);
return match(ConstantExpr::getICmp(ICmpInst::ICMP_EQ, C0, C1), m_One());
}
bool Constant::containsUndefElement() const {

18
unittests/IR/ConstantsTest.cpp
View File

@ -586,7 +586,8 @@ TEST(ConstantsTest, FoldGlobalVariablePtr) {
}
// Check that undefined elements in vector constants are matched
// correctly for both integer and floating-point types.
// correctly for both integer and floating-point types. Just don't
// crash on vectors of pointers (could be handled?).
TEST(ConstantsTest, isElementWiseEqual) {
LLVMContext Context;
@ -607,7 +608,6 @@ TEST(ConstantsTest, isElementWiseEqual) {
EXPECT_FALSE(C12U1->isElementWiseEqual(C12U2));
EXPECT_FALSE(C12U21->isElementWiseEqual(C12U2));
/* FIXME: This will crash.
Type *FltTy = Type::getFloatTy(Context);
Constant *CFU = UndefValue::get(FltTy);
Constant *CF1 = ConstantFP::get(FltTy, 1.0);
@ -621,7 +621,19 @@ TEST(ConstantsTest, isElementWiseEqual) {
EXPECT_TRUE(CF12U1->isElementWiseEqual(CF1211));
EXPECT_FALSE(CF12U2->isElementWiseEqual(CF12U1));
EXPECT_FALSE(CF12U1->isElementWiseEqual(CF12U2));
*/
PointerType *PtrTy = Type::getInt8PtrTy(Context);
Constant *CPU = UndefValue::get(PtrTy);
Constant *CP0 = ConstantPointerNull::get(PtrTy);
Constant *CP0000 = ConstantVector::get({CP0, CP0, CP0, CP0});
Constant *CP00U0 = ConstantVector::get({CP0, CP0, CPU, CP0});
Constant *CP00U = ConstantVector::get({CP0, CP0, CPU});
EXPECT_FALSE(CP0000->isElementWiseEqual(CP00U0));
EXPECT_FALSE(CP00U0->isElementWiseEqual(CP0000));
EXPECT_FALSE(CP0000->isElementWiseEqual(CP00U));
EXPECT_FALSE(CP00U->isElementWiseEqual(CP00U0));
}
} // end anonymous namespace