[PATCH] D129966: [ARM] Remove VBICimm if no cleared bits are demanded

[Dave Green via Phabricator via llvm-commits]

dmgreen added inline comments.


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Comment at: llvm/lib/Target/ARM/ARMISelLowering.cpp:19970
+    uint64_t Mask = ARM_AM::decodeVMOVModImm(ModImm, EltBits);
+    if ((OriginalDemandedBits & Mask) == 0)
+      return TLO.CombineTo(Op, Op0);
----------------
samtebbs wrote:
> Looks like VBIC uses the complement of the immediate. Does that need to be considered when checking `Mask`?
By "complement of the immediate", do you mean that it is the opposite of an And? If so then yes.
The way I think of it is that the BIC will clear any bits in the input where the mask is 1. If there are no bits that are cleared which are also demanded, then we don't need the BIC. In most of the tests the BIC is clearing the top bits (0xff00), which is a vmovl. The demanded bits are only the low bits (0x00ff).


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  https://reviews.llvm.org/D129966/new/

https://reviews.llvm.org/D129966