================
@@ -7170,16 +7165,31 @@ bool X86TTIImpl::isProfitableToSinkOperands(Instruction
*I,
II->getIntrinsicID() == Intrinsic::fshr)
ShiftAmountOpNum = 2;
}
-
if (ShiftAmountOpNum == -1)
return false;
+ auto *ShiftAmount = &I->getOperandUse(ShiftAmountOpNum);
- auto *Shuf = dyn_cast<ShuffleVectorInst>(I->getOperand(ShiftAmountOpNum));
+ // A uniform shift amount in a vector shift or funnel shift may be much
+ // cheaper than a generic variable vector shift, so make that pattern visible
+ // to SDAG by sinking the shuffle instruction next to the shift.
+ auto *Shuf = dyn_cast<ShuffleVectorInst>(ShiftAmount);
if (Shuf && getSplatIndex(Shuf->getShuffleMask()) >= 0 &&
isVectorShiftByScalarCheap(I->getType())) {
- Ops.push_back(&I->getOperandUse(ShiftAmountOpNum));
+ Ops.push_back(ShiftAmount);
return true;
}
+ // Casts taking a constant expression (generally derived from a global
+ // variable address) as an operand are profitable to sink because they appear
+ // as subexpressions in the instruction sequence generated by the
+ // LowerTypeTests pass which is expected to pattern match to the rotate
+ // instruction's immediate operand.
+ if (auto *CI = dyn_cast<CastInst>(ShiftAmount)) {
+ if (isa<ConstantExpr>(CI->getOperand(0))) {
+ Ops.push_back(ShiftAmount);
+ return true;
+ }
+ }
----------------
pcc wrote:
I would not generally expect normal user code to take the address of a global
variable and do constant arithmetic on it in such a way that it wouldn't
ultimately become an immediate operand to some instruction, so I didn't think
it would be worth detecting that case.
I also gave the fshr idea more thought. Thank you for sending #141735. I will
check if it improves or regresses the generated code. I will also check if we
can avoid using zext (instead use ptrtoint to i64 as the argument to fshr) and
avoid this issue entirely. I think there was some reason why this didn't work
with shl/shr/or though.
https://github.com/llvm/llvm-project/pull/141326
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