[FPEnv] EarlyCSE support for constrained intrinsics, default FP environment edition

EarlyCSE cannot distinguish between floating point instructions and
constrained floating point intrinsics that are marked as running in the
default FP environment. Said intrinsics are supposed to behave exactly the
same as the regular FP instructions. Teach EarlyCSE to handle them in that
case.

Differential Revision: https://reviews.llvm.org/D99962

Author: kpneal

llvm/include/llvm/IR/IntrinsicInst.h

@@ -432,6 +432,7 @@ class ConstrainedFPIntrinsic : public IntrinsicInst {
   bool isTernaryOp() const;
   Optional<RoundingMode> getRoundingMode() const;
   Optional<fp::ExceptionBehavior> getExceptionBehavior() const;
+  bool isDefaultFPEnvironment() const;
 
   // Methods for support type inquiry through isa, cast, and dyn_cast:
   static bool classof(const IntrinsicInst *I);

llvm/lib/IR/IntrinsicInst.cpp

@@ -172,8 +172,10 @@ Value *InstrProfIncrementInst::getStep() const {
 
 Optional<RoundingMode> ConstrainedFPIntrinsic::getRoundingMode() const {
   unsigned NumOperands = getNumArgOperands();
-  Metadata *MD =
-      cast<MetadataAsValue>(getArgOperand(NumOperands - 2))->getMetadata();
+  Metadata *MD = nullptr;
+  auto *MAV = dyn_cast<MetadataAsValue>(getArgOperand(NumOperands - 2));
+  if (MAV)
+    MD = MAV->getMetadata();
   if (!MD || !isa<MDString>(MD))
     return None;
   return StrToRoundingMode(cast<MDString>(MD)->getString());
@@ -182,13 +184,31 @@ Optional<RoundingMode> ConstrainedFPIntrinsic::getRoundingMode() const {
 Optional<fp::ExceptionBehavior>
 ConstrainedFPIntrinsic::getExceptionBehavior() const {
   unsigned NumOperands = getNumArgOperands();
-  Metadata *MD =
-      cast<MetadataAsValue>(getArgOperand(NumOperands - 1))->getMetadata();
+  Metadata *MD = nullptr;
+  auto *MAV = dyn_cast<MetadataAsValue>(getArgOperand(NumOperands - 1));
+  if (MAV)
+    MD = MAV->getMetadata();
   if (!MD || !isa<MDString>(MD))
     return None;
   return StrToExceptionBehavior(cast<MDString>(MD)->getString());
 }
 
+bool ConstrainedFPIntrinsic::isDefaultFPEnvironment() const {
+  Optional<fp::ExceptionBehavior> Except = getExceptionBehavior();
+  if (Except) {
+    if (Except.getValue() != fp::ebIgnore)
+      return false;
+  }
+
+  Optional<RoundingMode> Rounding = getRoundingMode();
+  if (Rounding) {
+    if (Rounding.getValue() != RoundingMode::NearestTiesToEven)
+      return false;
+  }
+
+  return true;
+}
+
 FCmpInst::Predicate ConstrainedFPCmpIntrinsic::getPredicate() const {
   Metadata *MD = cast<MetadataAsValue>(getArgOperand(2))->getMetadata();
   if (!MD || !isa<MDString>(MD))

llvm/lib/Transforms/Scalar/EarlyCSE.cpp

@@ -108,8 +108,29 @@ struct SimpleValue {
 
   static bool canHandle(Instruction *Inst) {
     // This can only handle non-void readnone functions.
-    if (CallInst *CI = dyn_cast<CallInst>(Inst))
+    // Also handled are constrained intrinsic that look like the types
+    // of instruction handled below (UnaryOperator, etc.).
+    if (CallInst *CI = dyn_cast<CallInst>(Inst)) {
+      if (Function *F = CI->getCalledFunction()) {
+        switch ((Intrinsic::ID)F->getIntrinsicID()) {
+        case Intrinsic::experimental_constrained_fadd:
+        case Intrinsic::experimental_constrained_fsub:
+        case Intrinsic::experimental_constrained_fmul:
+        case Intrinsic::experimental_constrained_fdiv:
+        case Intrinsic::experimental_constrained_frem:
+        case Intrinsic::experimental_constrained_fptosi:
+        case Intrinsic::experimental_constrained_sitofp:
+        case Intrinsic::experimental_constrained_fptoui:
+        case Intrinsic::experimental_constrained_uitofp:
+        case Intrinsic::experimental_constrained_fcmp:
+        case Intrinsic::experimental_constrained_fcmps: {
+          auto *CFP = cast<ConstrainedFPIntrinsic>(CI);
+          return CFP->isDefaultFPEnvironment();
+        }
+        }
+      }
       return CI->doesNotAccessMemory() && !CI->getType()->isVoidTy();
+    }
     return isa<CastInst>(Inst) || isa<UnaryOperator>(Inst) ||
            isa<BinaryOperator>(Inst) || isa<GetElementPtrInst>(Inst) ||
            isa<CmpInst>(Inst) || isa<SelectInst>(Inst) ||