[llvm] [InstCombine] Fold fptoui(fadd(uitofp(X), C)) to X (PR #210588)

[Lucas Ly Ba via llvm-commits]

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@@ -2581,10 +2580,58 @@ static Instruction *foldFPtoI(Instruction &FI, InstCombiner &IC) {
                   : BinaryOperator::CreateUDiv(X, C);
 }
 
+// fptoui (fadd (uitofp X), C) --> X
+//
+// X is already an integer, so if 0 <= C < 1 and X fits exactly in the float,
+// adding C can't reach the next integer and fptoui just gives X back. This is
+// the (unsigned)((float)x + 0.5f) rounding trick.
+static Value *foldFPToUIOfUIToFPInc(FPToUIInst &FI) {
+  Value *X;
+  const APFloat *C;
+  if (!match(FI.getOperand(0), m_FAdd(m_UIToFP(m_Value(X)), m_APFloat(C))))
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lucasly-ba wrote:

yes fixed it !

https://github.com/llvm/llvm-project/pull/210588