[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
diff --git a/llvm/lib/Target/PowerPC/PPCQPXLoadSplat.cpp b/llvm/lib/Target/PowerPC/PPCQPXLoadSplat.cpp
index 642b90e..816f05f 100644
--- a/llvm/lib/Target/PowerPC/PPCQPXLoadSplat.cpp
+++ b/llvm/lib/Target/PowerPC/PPCQPXLoadSplat.cpp
@@ -130,7 +130,15 @@
}
}
- 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;
}