[llvm] [InstCombine] Add combines for unsigned comparison of absolute value to constant (PR #172021)

[Yingwei Zheng via llvm-commits]

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@@ -7602,6 +7602,51 @@ Instruction *InstCombinerImpl::foldICmpCommutative(CmpPredicate Pred,
     }
   }
 
+  // abs(X) u> K --> K >= 0 ? `X + K u> 2 * K`              : `false`
+  // If abs(INT_MIN) is poison:
+  // abs(X) u< K --> K >= 1 ? `X + (K - 1) u<= 2 * (K - 1)` : K != 0
+  {
+    Value *X;
+    ConstantInt *C, *K;
+    bool Frozen = false;
+    if ((match(Op0,
+               m_Intrinsic<Intrinsic::abs>(m_Value(X), m_ConstantInt(C))) ||
+         (Frozen = match(Op0, m_Freeze(m_Intrinsic<Intrinsic::abs>(
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dtcxzyw wrote:

We don't care about this case. If there is a freeze instruction blocking pattern matching, we can push the freeze through the abs in the future. See also pushFreezeToPreventPoisonFromPropagating.

https://github.com/llvm/llvm-project/pull/172021