[PowerPC] Fix and(or(x, c1), c2) -> rlwimi generation
PPCISelDAGToDAG has a transformation that generates a rlwimi instruction from
an input pattern that looks like this:
and(or(x, c1), c2)
but the associated logic does not work if there are bits that are 1 in c1 but 0
in c2 (these are normally canonicalized away, but that can't happen if the 'or'
has other users. Make sure we abort the transformation if such bits are
discovered.
Fixes PR24704.
llvm-svn: 246900
diff --git a/llvm/lib/Target/PowerPC/PPCISelDAGToDAG.cpp b/llvm/lib/Target/PowerPC/PPCISelDAGToDAG.cpp
index 0b43b04..30d792e 100644
--- a/llvm/lib/Target/PowerPC/PPCISelDAGToDAG.cpp
+++ b/llvm/lib/Target/PowerPC/PPCISelDAGToDAG.cpp
@@ -2570,13 +2570,25 @@
return nullptr;
}
// ISD::OR doesn't get all the bitfield insertion fun.
- // (and (or x, c1), c2) where isRunOfOnes(~(c1^c2)) is a bitfield insert
+ // (and (or x, c1), c2) where isRunOfOnes(~(c1^c2)) might be a
+ // bitfield insert.
if (isInt32Immediate(N->getOperand(1), Imm) &&
N->getOperand(0).getOpcode() == ISD::OR &&
isInt32Immediate(N->getOperand(0).getOperand(1), Imm2)) {
+ // The idea here is to check whether this is equivalent to:
+ // (c1 & m) | (x & ~m)
+ // where m is a run-of-ones mask. The logic here is that, for each bit in
+ // c1 and c2:
+ // - if both are 1, then the output will be 1.
+ // - if both are 0, then the output will be 0.
+ // - if the bit in c1 is 0, and the bit in c2 is 1, then the output will
+ // come from x.
+ // - if the bit in c1 is 1, and the bit in c2 is 0, then the output will
+ // be 0.
+ // If that last condition is never the case, then we can form m from the
+ // bits that are the same between c1 and c2.
unsigned MB, ME;
- Imm = ~(Imm^Imm2);
- if (isRunOfOnes(Imm, MB, ME)) {
+ if (isRunOfOnes(~(Imm^Imm2), MB, ME) && !(~Imm & Imm2)) {
SDValue Ops[] = { N->getOperand(0).getOperand(0),
N->getOperand(0).getOperand(1),
getI32Imm(0, dl), getI32Imm(MB, dl),