[llvm] Optimize fptrunc(x)>=C1 --> x>=C2 (PR #99475)
Matt Arsenault via llvm-commits
llvm-commits at lists.llvm.org
Sun Oct 20 16:08:41 PDT 2024
================
@@ -7882,6 +7892,93 @@ static Instruction *foldFCmpReciprocalAndZero(FCmpInst &I, Instruction *LHSI,
return new FCmpInst(Pred, LHSI->getOperand(1), RHSC, "", &I);
}
+// Fold fptrunc(x) < constant --> x < constant if possible.
+static Instruction *foldFCmpFpTrunc(FCmpInst &I, Instruction *LHSI,
+ Constant *RHSC) {
+ FCmpInst::Predicate Pred = I.getPredicate();
+ bool RoundDown = false;
+
+ if (Pred == FCmpInst::FCMP_OGE || Pred == FCmpInst::FCMP_UGE ||
+ Pred == FCmpInst::FCMP_OLT || Pred == FCmpInst::FCMP_ULT)
+ RoundDown = true;
+ else if (Pred == FCmpInst::FCMP_OGT || Pred == FCmpInst::FCMP_UGT ||
+ Pred == FCmpInst::FCMP_OLE || Pred == FCmpInst::FCMP_ULE)
+ RoundDown = false;
+ else
+ return nullptr;
+
+ const APFloat *RValue;
+ if (!match(RHSC, m_APFloat(RValue)))
+ return nullptr;
+
+ // RHSC should not be nan or infinity.
+ if (RValue->isNaN() || RValue->isInfinity())
+ return nullptr;
+
+ Type *LType = LHSI->getOperand(0)->getType();
+ Type *RType = RHSC->getType();
+ Type *LEleType = LType->getScalarType();
+ Type *REleType = RType->getScalarType();
+
+ APFloat NextRValue = *RValue;
+ NextRValue.next(RoundDown);
+
+ // Round RValue to suitable value
+ APFloat ExtRValue = *RValue;
+ APFloat ExtNextRValue = NextRValue;
+ bool lossInfo;
+ ExtRValue.convert(LEleType->getFltSemantics(), APFloat::rmNearestTiesToEven,
+ &lossInfo);
+ ExtNextRValue.convert(LEleType->getFltSemantics(),
+ APFloat::rmNearestTiesToEven, &lossInfo);
+
+ // Binary search to find the maximal (or minimal) value after RValue promotion.
+ // RValue can't have special comparison rules, which means nan or inf is not
+ // allowed here.
+ APFloat RoundValue{LEleType->getFltSemantics()};
+ {
+ APFloat Two{LEleType->getFltSemantics(), 2};
+
+ // The (negative) maximum of RValue will become infinity when rounded up (down).
+ // Set the limit of ExtNextRValue.
+ if (NextRValue.isInfinity()) {
+ ExtNextRValue = ExtRValue * Two;
+ }
----------------
arsenm wrote:
No braces. Can also defer construction of the 2 constant (or avoid it by using scalbn instead)
https://github.com/llvm/llvm-project/pull/99475
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