[PATCH] D47681: [DAGCombiner] Bug 31275- Extract a shift from a constant mul or udiv if a rotate can be formed

[Simon Pilgrim via Phabricator via llvm-commits]

RKSimon added a comment.

I've added your tests to trunk with current codegen so you need to rebase, which will show the effects of your patch.



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Comment at: lib/CodeGen/SelectionDAG/DAGCombiner.cpp:5049
+  // op0 must be the same opcode on both sides, have the same LHS argument, and
+  // produce the same value type
+  SDValue OppShiftLHS = OppShift.getOperand(0);
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(style) full stops at the end of comments.


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Comment at: lib/CodeGen/SelectionDAG/DAGCombiner.cpp:5063
+  ConstantSDNode *ExtractFromCst =
+      isConstOrConstSplat(ExtractFrom.getOperand(1));
+  // Check that we have constant values
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It'd be great if this could support non-uniform constant vectors but a TODO comment is fine for now.


https://reviews.llvm.org/D47681