[InstCombine] canonicalize fcmp+select to minnum/maxnum intrinsics

This is the opposite direction of D62158 (we have to choose 1 form or the other).
Now that we have FMF on the select, this becomes more palatable. And the benefits
of having a single IR instruction for this operation (less chances of missing folds
based on extra uses, etc) overcome my previous comments about the potential advantage
of larger pattern matching/analysis.

Differential Revision: https://reviews.llvm.org/D62414

llvm-svn: 364721

1 files changed, 13 insertions, 0 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp b/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
index c6d2acac155..7a3c2b96658 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
@@ -2030,6 +2030,19 @@ Instruction *InstCombiner::visitSelectInst(SelectInst &SI) {
     }
   }
 
+  // Canonicalize select of FP values where NaN and -0.0 are not valid as
+  // minnum/maxnum intrinsics.
+  if (isa<FPMathOperator>(SI) && SI.hasNoNaNs() && SI.hasNoSignedZeros()) {
+    Value *X, *Y;
+    if (match(&SI, m_OrdFMax(m_Value(X), m_Value(Y))))
+      return replaceInstUsesWith(
+          SI, Builder.CreateBinaryIntrinsic(Intrinsic::maxnum, X, Y, &SI));
+
+    if (match(&SI, m_OrdFMin(m_Value(X), m_Value(Y))))
+      return replaceInstUsesWith(
+          SI, Builder.CreateBinaryIntrinsic(Intrinsic::minnum, X, Y, &SI));
+  }
+
   // See if we can fold the select into a phi node if the condition is a select.
   if (auto *PN = dyn_cast<PHINode>(SI.getCondition()))
     // The true/false values have to be live in the PHI predecessor's blocks.