[PATCH] D117210: [CodeGen] Support folds of not(cmp(cc, ...)) -> cmp(!cc, ...) for scalable vectors

[Fraser Cormack via Phabricator via llvm-commits]

frasercrmck added inline comments.


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Comment at: llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp:3175
+             isa<ConstantSDNode>(N->getOperand(0))) {
+    CVal = cast<ConstantSDNode>(N->getOperand(0))->getAPIntValue();
   } else {
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david-arm wrote:
> frasercrmck wrote:
> > I think we have to support the truncating case as with `BUILD_VECTOR` above, don't we?
> Hmm, I looked at the definition of SPLAT_VECTOR and you're right - the operand is allowed to be wider than the vector element type of the result. I hadn't realised that :(. The only problem is that I have absolutely no idea how to write a test case for this using IR! I'm not sure if there is a way to create a splat (using SPLAT_VECTOR) in IR that is truncating. Unless you know of any RISCV examples where this would happen?
Hmm, it would definitely happen during legalization as we only have either i32 (RV32) or i64 (RV64) as legal integer types, so most splats, really, like `<vscale x 1 x i8>` with a constant integer. But you'd need to be calling this during/after legalization. So no I'm not sure it's testable, per se. What you've got looks right, though?


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https://reviews.llvm.org/D117210