[llvm] [IA][RISCV] Recognizing gap masks assembled from bitwise AND (PR #153324)

[Craig Topper via llvm-commits]

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@@ -601,6 +602,18 @@ static std::pair<Value *, APInt> getMask(Value *WideMask, unsigned Factor,
     }
   }
 
+  // Try to match `and <interleaved mask>, <gap mask>`. The WideMask here is
+  // expected to be a fixed vector and gap mask should be a constant mask.
+  Value *AndMaskLHS;
+  Constant *AndMaskRHS;
+  if (LeafValueEC.isFixed() &&
+      match(WideMask, m_c_And(m_Value(AndMaskLHS), m_Constant(AndMaskRHS)))) {
+    assert(!isa<Constant>(AndMaskLHS) &&
+           "expect constants to be folded already");
+    getGapMask(*AndMaskRHS, Factor, LeafValueEC.getFixedValue(), GapMask);
+    return {getMask(AndMaskLHS, Factor, LeafValueEC).first, GapMask};
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topperc wrote:

> InstCombine

I don't think it is a good idea to make assumptions about what earlier passes will do. We don't have to produce optimal code if both operands are constants or the constant is on the left hand side instead of the right. But we cannot write an assert that says it will not happen.

https://github.com/llvm/llvm-project/pull/153324