[PATCH] D102969: [GlobalISel] Add G_SBFX/G_UBFX to computeKnownBits

Fri May 28 03:45:58 PDT 2021

RKSimon added inline comments.

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Comment at: llvm/lib/CodeGen/GlobalISel/GISelKnownBits.cpp:514
+        WidthKnown.getMinValue().getLimitedValue(BitWidth));
+    Known = KnownBits::lshr(SrcOpKnown, OffsetKnown) & Mask;
+    if (Opcode == TargetOpcode::G_SBFX) {
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foad wrote:
> RKSimon wrote:
> > Are you going to have any issues here when Mask.hasConflict() is true?
> That can only happen if WidthKnown.getMinValue() > WidthKnown.getMaxValue(), which I guess can only happen if WidthKnown.hasConflict() was already true. What are the rules about introducing or propagating conflicts?
Well, we do assert there is no conflict at the end of GISelKnownBits::computeKnownBitsImpl so we should be ensuring this doesn't happen.

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D102969/new/

https://reviews.llvm.org/D102969