[PATCH] D34077: DAGCombine: Combine BUILD_VECTOR to TRUNCATE

[Zvi Rackover via Phabricator via llvm-commits]

zvi added inline comments.


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Comment at: lib/CodeGen/SelectionDAG/DAGCombiner.cpp:14272
+  // Proceed only if the stride and the types can be matched to a truncate.
+  if ((Stride == 1 || !isPowerOf2_32(Stride)) ||
+      (ExtractedFromVec.getValueType().getVectorNumElements() !=
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delena wrote:
> I'd check (Stride < 2), I don't know what isPowerOf2_32() thinks about 0.
 isPowerOf2_32(0) should return false. From a quick look at the implementation this is the case. I will add a case in unittests/Support/MathExtrasTest.cpp to make sure this is covered.


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Comment at: lib/CodeGen/SelectionDAG/DAGCombiner.cpp:14296
+  Res = DAG.getNode(ISD::TRUNCATE, SDLoc(N), TruncVT, Res);
+  if (VT.isFloatingPoint())
+    Res = DAG.getBitcast(VT, Res);
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delena wrote:
> you can just call for getBitcast(VT, Res), the "getBitcast() has the "if" inside".
ok.


https://reviews.llvm.org/D34077