[PATCH] D128769: [DAGCombiner][X86] Fold sra (sub AddC, (shl X, N1C)), N1C --> sext (sub AddC1',(trunc X to (width - N1C)))

Sat Jul 9 04:57:35 PDT 2022

RKSimon accepted this revision.
RKSimon added a comment.
This revision is now accepted and ready to land.

LGTM

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Comment at: llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp:9300
+      if (ConstantSDNode *AddC =
+              isConstOrConstSplat(N0.getOperand(IsAdd ? 1 : 0))) {
+        // Determine what the truncate's type would be and ask the target if
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craig.topper wrote:
> RKSimon wrote:
> > Does this have to be a splat? I think technically only N1C has to be and AddC can be non-uniform except it requires the ShiftC calculation to be refactored for general constant folding. But I'm not certain how often isTruncateFree is going to return true for vector types....
> I think you're right, but I'd rather not do that in this patch.
OK - please can you add a TODO comment?

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https://reviews.llvm.org/D128769