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[UnreachableBlockElim] Check return value of constrainRegClass().

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Summary:
MachineRegisterInfo::constrainRegClass() can fail if two register classes
don't have a common subclass or if the register class doesn't contain
enough registers. Check the return value before trying to remove Phi nodes,
and if we can't constrain, we output a COPY instead of simply replacing
registers.

Reviewers: kparzysz, david2050, wmi

Reviewed By: kparzysz

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D32999

llvm-svn: 302622
This commit is contained in:
Mikael Holmen 2017-05-10 06:33:43 +00:00
parent d7292f3867
commit 41f55d04e2
1 changed files with 4 additions and 3 deletions
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7
lib/CodeGen/UnreachableBlockElim.cpp
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@ -206,11 +206,12 @@ bool UnreachableMachineBlockElim::runOnMachineFunction(MachineFunction &F) {
if (InputReg != OutputReg) {
MachineRegisterInfo &MRI = F.getRegInfo();
unsigned InputSub = Input.getSubReg();
if (InputSub == 0) {
MRI.constrainRegClass(InputReg, MRI.getRegClass(OutputReg));
if (InputSub == 0 &&
MRI.constrainRegClass(InputReg, MRI.getRegClass(OutputReg))) {
MRI.replaceRegWith(OutputReg, InputReg);
} else {
// The input register to the PHI has a subregister:
// The input register to the PHI has a subregister or it can't be
// constrained to the proper register class:
// insert a COPY instead of simply replacing the output
// with the input.
const TargetInstrInfo *TII = F.getSubtarget().getInstrInfo();