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[GlobalISel][KnownBits] Early return on out of bound shift amounts 

If the known shift amount is bigger than or equal to the bitwidth of the type of the value to be shifted,
the result is target dependent, so don't try to infer any bits.

This fixes a crash we've seen in one of our internal test suites.

Reviewed By: arsenm

Differential Revision: https://reviews.llvm.org/D89232
This commit is contained in:
Konstantin Schwarz 2020-10-12 11:45:33 +02:00
parent 2f66bfac28
commit 7341123439
2 changed files with 39 additions and 0 deletions
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4
llvm/lib/CodeGen/GlobalISel/GISelKnownBits.cpp
View File

@ -397,6 +397,10 @@ void GISelKnownBits::computeKnownBitsImpl(Register R, KnownBits &Known,
uint64_t Shift = RHSKnown.getConstant().getZExtValue();
LLVM_DEBUG(dbgs() << '[' << Depth << "] Shift is " << Shift << '\n');
// Guard against oversized shift amounts
if (Shift >= MRI.getType(MI.getOperand(1).getReg()).getScalarSizeInBits())
break;
computeKnownBitsImpl(MI.getOperand(1).getReg(), Known, DemandedElts,
Depth + 1);

35
llvm/unittests/CodeGen/GlobalISel/KnownBitsTest.cpp
View File

@ -725,3 +725,38 @@ TEST_F(AArch64GISelMITest, TestKnownBitsUMax) {
EXPECT_EQ(0xffu, KnownUmax.Zero.getZExtValue());
EXPECT_EQ(0xffffffffffffff00, KnownUmax.One.getZExtValue());
}
TEST_F(AArch64GISelMITest, TestInvalidQueries) {
StringRef MIRString = R"(
%src:_(s32) = COPY $w0
%thirty2:_(s32) = G_CONSTANT i32 32
%equalSized:_(s32) = G_SHL %src, %thirty2
%copy1:_(s32) = COPY %equalSized
%thirty3:_(s32) = G_CONSTANT i32 33
%biggerSized:_(s32) = G_SHL %src, %thirty3
%copy2:_(s32) = COPY %biggerSized
)";
setUp(MIRString);
if (!TM)
return;
Register EqSizedCopyReg = Copies[Copies.size() - 2];
MachineInstr *EqSizedCopy = MRI->getVRegDef(EqSizedCopyReg);
Register EqSizedShl = EqSizedCopy->getOperand(1).getReg();
Register BiggerSizedCopyReg = Copies[Copies.size() - 1];
MachineInstr *BiggerSizedCopy = MRI->getVRegDef(BiggerSizedCopyReg);
Register BiggerSizedShl = BiggerSizedCopy->getOperand(1).getReg();
GISelKnownBits Info(*MF);
KnownBits EqSizeRes = Info.getKnownBits(EqSizedShl);
KnownBits BiggerSizeRes = Info.getKnownBits(BiggerSizedShl);
// We don't know what the result of the shift is, but we should not crash
EXPECT_TRUE(EqSizeRes.One.isNullValue());
EXPECT_TRUE(EqSizeRes.Zero.isNullValue());
EXPECT_TRUE(BiggerSizeRes.One.isNullValue());
EXPECT_TRUE(BiggerSizeRes.Zero.isNullValue());
}