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[PowerPC/QPX] Fix the load/splat peephole with overlapping reads 

If, in between the splat and the load (which does an implicit splat), there is
a read of the splat register, then that register must have another earlier
definition. In that case, we can't replace the load's destination register with
the splat's destination register.

Unfortunately, I don't have a small or non-fragile test case.

llvm-svn: 268152
This commit is contained in:
Hal Finkel 2016-04-30 01:59:28 +00:00
parent dc4531e552
commit 17e9754dd4
1 changed files with 9 additions and 1 deletions
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10
llvm/lib/Target/PowerPC/PPCQPXLoadSplat.cpp
View File

@ -130,7 +130,15 @@ bool PPCQPXLoadSplat::runOnMachineFunction(MachineFunction &MF) {
}
}
if (MI->modifiesRegister(SplatReg, TRI)) {
// If this instruction defines the splat register, then we cannot move
// the previous definition above it. If it reads from the splat
// register, then it must already be alive from some previous
// definition, and if the splat register is different from the source
// register, then this definition must not be the load for which we're
// searching.
if (MI->modifiesRegister(SplatReg, TRI) ||
(SrcReg != SplatReg &&
MI->readsRegister(SplatReg, TRI))) {
SI = Splats.erase(SI);
continue;
}