[llvm] Optimize fptrunc(x)>=C1 --> x>=C2 (PR #99475)

[Matt Arsenault via llvm-commits]

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@@ -7882,6 +7885,30 @@ static Instruction *foldFCmpReciprocalAndZero(FCmpInst &I, Instruction *LHSI,
   return new FCmpInst(Pred, LHSI->getOperand(1), RHSC, "", &I);
 }
 
+// Fold trunc(x) < constant --> x < constant if possible.
+static Instruction *foldFCmpFpTrunc(FCmpInst &I, Instruction *LHSI,
+                                    Constant *RHSC) {
+  //
+  FCmpInst::Predicate Pred = I.getPredicate();
+
+  // Check that predicates are valid.
+  if ((Pred != FCmpInst::FCMP_OGT) && (Pred != FCmpInst::FCMP_OLT) &&
+      (Pred != FCmpInst::FCMP_OGE) && (Pred != FCmpInst::FCMP_OLE))
+    return nullptr;
+
+  auto *LType = LHSI->getOperand(0)->getType();
+  auto *RType = RHSC->getType();
+
+  if (!(LType->isFloatingPointTy() && RType->isFloatingPointTy() &&
+        LType->getTypeID() >= RType->getTypeID()))
+    return nullptr;
+
+  auto *ROperand = llvm::ConstantFP::get(
+      LType, dyn_cast<ConstantFP>(RHSC)->getValue().convertToDouble());
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arsenm wrote:

Don't use convertToDouble, keep this entirely in APFloat 

https://github.com/llvm/llvm-project/pull/99475