[llvm] [llvm] [InstCombine] fold "icmp eq (X + (V - 1)) & -V, X" to "icmp eq (and X, V - 1), 0" (PR #152851)

[Nikita Popov via llvm-commits]

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@@ -1320,6 +1320,40 @@ Instruction *InstCombinerImpl::foldICmpWithZero(ICmpInst &Cmp) {
   return nullptr;
 }
 
+// Fold icmp eq (num + (val - 1)) & -val, num
+//      to
+//      icmp eq 0, (and num, val - 1)
+// For value being power of two
+Instruction *InstCombinerImpl::foldIsMultipleOfAPowerOfTwo(ICmpInst &Cmp) {
+  Value *Neg, *Num, *Mask;
+  CmpPredicate Pred;
+  const APInt *NegConst, *MaskConst;
+
+  if (!match(&Cmp, m_c_ICmp(Pred, m_Value(Num),
+                            m_OneUse(m_c_And(m_OneUse(m_c_Add(m_Deferred(Num),
+                                                              m_Value(Mask))),
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nikic wrote:

Oh right, we can't use m_SpecificInt with a value captured in the same match.

https://github.com/llvm/llvm-project/pull/152851