[InstCombine] narrow select with FP casts
Select doesn't change values, so truncate of extended operand cancels out.
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
index 53bcaeb..8d8b2f9 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
@@ -1636,6 +1636,24 @@
return BinaryOperator::CreateFNegFMF(InnerTrunc, Op);
return UnaryOperator::CreateFNegFMF(InnerTrunc, Op);
}
+
+ // If we are truncating a select that has an extended operand, we can
+ // narrow the other operand and do the select as a narrow op.
+ Value *Cond, *X, *Y;
+ if (match(Op, m_Select(m_Value(Cond), m_FPExt(m_Value(X)), m_Value(Y))) &&
+ X->getType() == Ty) {
+ // fptrunc (select Cond, (fpext X), Y --> select Cond, X, (fptrunc Y)
+ Value *NarrowY = Builder.CreateFPTrunc(Y, Ty);
+ Value *Sel = Builder.CreateSelect(Cond, X, NarrowY, "narrow.sel", Op);
+ return replaceInstUsesWith(FPT, Sel);
+ }
+ if (match(Op, m_Select(m_Value(Cond), m_Value(Y), m_FPExt(m_Value(X)))) &&
+ X->getType() == Ty) {
+ // fptrunc (select Cond, Y, (fpext X) --> select Cond, (fptrunc Y), X
+ Value *NarrowY = Builder.CreateFPTrunc(Y, Ty);
+ Value *Sel = Builder.CreateSelect(Cond, NarrowY, X, "narrow.sel", Op);
+ return replaceInstUsesWith(FPT, Sel);
+ }
}
if (auto *II = dyn_cast<IntrinsicInst>(FPT.getOperand(0))) {