maxjhandsome
/
llvm-project
forked from OSchip/llvm-project
1
0
Fork 0
Code Issues Pull Requests Packages Releases Wiki Activity

[GlobalISel] Fix computing known bits for loads with range metadata 

In GlobalISel, if you have a load into a small type with a range, you'll hit
an assert if you try to compute known bits on it starting at a larger type.

e.g.

```
%x:_(s8) = G_LOAD %whatever(p0) :: (load 1 ... !range !n)
...
%y:_(s32) = G_SOMETHING %x
```

When we walk through G_SOMETHING and hit the load, the width of our known bits
is 32. However, the width of the range is going to be 8. This will cause us
to hit an assert.

To fix this, make computeKnownBitsFromRangeMetadata zero extend or truncate
the range type to match the bitwidth of the known bits we're calculating.

Add a testcase in CodeGen/GlobalISel/KnownBitsTest.cpp to reflect that this
works now.

https://reviews.llvm.org/D85375
This commit is contained in:
Jessica Paquette 2020-08-05 16:32:55 -07:00
parent 243903f326
commit c8a282bcf7
2 changed files with 51 additions and 3 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

6
llvm/lib/Analysis/ValueTracking.cpp
View File

@ -549,10 +549,10 @@ void llvm::computeKnownBitsFromRangeMetadata(const MDNode &Ranges,
// The first CommonPrefixBits of all values in Range are equal.
unsigned CommonPrefixBits =
(Range.getUnsignedMax() ^ Range.getUnsignedMin()).countLeadingZeros();
APInt Mask = APInt::getHighBitsSet(BitWidth, CommonPrefixBits);
Known.One &= Range.getUnsignedMax() & Mask;
Known.Zero &= ~Range.getUnsignedMax() & Mask;
APInt UnsignedMax = Range.getUnsignedMax().zextOrTrunc(BitWidth);
Known.One &= UnsignedMax & Mask;
Known.Zero &= ~UnsignedMax & Mask;
}
}

48
llvm/unittests/CodeGen/GlobalISel/KnownBitsTest.cpp
View File

@ -463,3 +463,51 @@ TEST_F(AMDGPUGISelMITest, TestTargetKnownAlign) {
EXPECT_EQ(Align(4), Info.computeKnownAlignment(CopyImplicitArgPtr));
EXPECT_EQ(Align(4), Info.computeKnownAlignment(CopyImplicitBufferPtr));
}
TEST_F(AArch64GISelMITest, TestMetadata) {
StringRef MIRString = " %imp:_(p0) = G_IMPLICIT_DEF\n"
" %load:_(s8) = G_LOAD %imp(p0) :: (load 1)\n"
" %ext:_(s32) = G_ZEXT %load(s8)\n"
" %cst:_(s32) = G_CONSTANT i32 1\n"
" %and:_(s32) = G_AND %ext, %cst\n"
" %copy:_(s32) = COPY %and(s32)\n";
setUp(MIRString);
if (!TM)
return;
Register CopyReg = Copies[Copies.size() - 1];
MachineInstr *FinalCopy = MRI->getVRegDef(CopyReg);
Register SrcReg = FinalCopy->getOperand(1).getReg();
// We need a load with a metadata range for this to break. Fudge the load in
// the string and replace it with something we can work with.
MachineInstr *And = MRI->getVRegDef(SrcReg);
MachineInstr *Ext = MRI->getVRegDef(And->getOperand(1).getReg());
MachineInstr *Load = MRI->getVRegDef(Ext->getOperand(1).getReg());
IntegerType *Int8Ty = Type::getInt8Ty(Context);
// Value must be in [0, 2)
Metadata *LowAndHigh[] = {
ConstantAsMetadata::get(ConstantInt::get(Int8Ty, 0)),
ConstantAsMetadata::get(ConstantInt::get(Int8Ty, 2))};
auto NewMDNode = MDNode::get(Context, LowAndHigh);
const MachineMemOperand *OldMMO = *Load->memoperands_begin();
MachineMemOperand NewMMO(OldMMO->getPointerInfo(), OldMMO->getFlags(),
OldMMO->getSizeInBits(), OldMMO->getAlign(),
OldMMO->getAAInfo(), NewMDNode);
MachineIRBuilder MIB(*Load);
MIB.buildLoad(Load->getOperand(0), Load->getOperand(1), NewMMO);
Load->eraseFromParent();
GISelKnownBits Info(*MF);
KnownBits Res = Info.getKnownBits(And->getOperand(1).getReg());
// We don't know what the result of the load is, so we don't know any ones.
EXPECT_TRUE(Res.One.isNullValue());
// We know that the value is in [0, 2). So, we don't know if the first bit
// is 0 or not. However, we do know that every other bit must be 0.
APInt Mask(Res.getBitWidth(), 1);
Mask.flipAllBits();
EXPECT_EQ(Mask.getZExtValue(), Res.Zero.getZExtValue());
}