[InstCombine] Canonicalize clamp of float types to minmax in fast mode.

Summary:
This commit allows matchSelectPattern to recognize clamp of float
arguments in the presence of FMF the same way as already done for
integers.

This case is a little different though. With integers, given the
min/max pattern is recognized, DAGBuilder starts selecting MIN/MAX
"automatically". That is not the case for float, because for them only
full FMINNAN/FMINNUM/FMAXNAN/FMAXNUM ISD nodes exist and they do care
about NaNs. On the other hand, some backends (e.g. X86) have only
FMIN/FMAX nodes that do not care about NaNS and the former NAN/NUM
nodes are illegal thus selection is not happening. So I decided to do
such kind of transformation in IR (InstCombiner) instead of
complicating the logic in the backend.

Reviewers: spatel, jmolloy, majnemer, efriedma, craig.topper

Reviewed By: efriedma

Subscribers: hiraditya, javed.absar, n.bozhenov, llvm-commits

Patch by Andrei Elovikov <andrei.elovikov@intel.com>

Differential Revision: https://reviews.llvm.org/D33186

llvm-svn: 310054

1 files changed, 17 insertions, 7 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp b/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
index 7ea00e0b163..0abff6b9268 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
@@ -1389,9 +1389,17 @@ Instruction *InstCombiner::visitSelectInst(SelectInst &SI) {
     auto SPF = SPR.Flavor;
 
     if (SelectPatternResult::isMinOrMax(SPF)) {
-      // Canonicalize so that type casts are outside select patterns.
-      if (LHS->getType()->getPrimitiveSizeInBits() !=
-          SelType->getPrimitiveSizeInBits()) {
+      // Canonicalize so that
+      // - type casts are outside select patterns.
+      // - float clamp is transformed to min/max pattern
+
+      bool IsCastNeeded = LHS->getType() != SelType;
+      Value *CmpLHS = cast<CmpInst>(CondVal)->getOperand(0);
+      Value *CmpRHS = cast<CmpInst>(CondVal)->getOperand(1);
+      if (IsCastNeeded ||
+          (LHS->getType()->isFPOrFPVectorTy() &&
+           ((CmpLHS != LHS && CmpLHS != RHS) ||
+            (CmpRHS != LHS && CmpRHS != RHS)))) {
         CmpInst::Predicate Pred = getCmpPredicateForMinMax(SPF, SPR.Ordered);
 
         Value *Cmp;
@@ -1404,10 +1412,12 @@ Instruction *InstCombiner::visitSelectInst(SelectInst &SI) {
           Cmp = Builder.CreateFCmp(Pred, LHS, RHS);
         }
 
-        Value *NewSI = Builder.CreateCast(
-            CastOp, Builder.CreateSelect(Cmp, LHS, RHS, SI.getName(), &SI),
-            SelType);
-        return replaceInstUsesWith(SI, NewSI);
+        Value *NewSI = Builder.CreateSelect(Cmp, LHS, RHS, SI.getName(), &SI);
+        if (!IsCastNeeded)
+          return replaceInstUsesWith(SI, NewSI);
+
+        Value *NewCast = Builder.CreateCast(CastOp, NewSI, SelType);
+        return replaceInstUsesWith(SI, NewCast);
       }
     }