Teach the IRBuilder about constrained FPTrunc and FPExt

[kpn]

Summary

The IRBuilder doesn't know that FPTrunc and FPExt have constrained equivalents. This patch adds the support by building on the strict FP mode now present in the IRBuilder.

[rjmccall]

LGTM

[kpn]

Thanks for the fast review!

include/llvm/IR/IRBuilder.h

public:
   }
 
   Value *CreateSIToFP(Value *V, Type *DestTy, const Twine &Name = ""){
     return CreateCast(Instruction::SIToFP, V, DestTy, Name);
   }
 
   Value *CreateFPTrunc(Value *V, Type *DestTy,
                        const Twine &Name = "") {
+    if (IsFPConstrained)
+      return CreateConstrainedFPCast(
+          Intrinsic::experimental_constrained_fptrunc, V, DestTy, nullptr,
+          Name);
     return CreateCast(Instruction::FPTrunc, V, DestTy, Name);
   }
 
   Value *CreateFPExt(Value *V, Type *DestTy, const Twine &Name = "") {
+    if (IsFPConstrained)
+      return CreateConstrainedFPCast(Intrinsic::experimental_constrained_fpext,
+                                     V, DestTy, nullptr, Name);
     return CreateCast(Instruction::FPExt, V, DestTy, Name);
   }
 
   Value *CreatePtrToInt(Value *V, Type *DestTy,
                         const Twine &Name = "") {
     return CreateCast(Instruction::PtrToInt, V, DestTy, Name);
   }
 
public:
   Value *CreateFPCast(Value *V, Type *DestTy, const Twine &Name = "") {
     if (V->getType() == DestTy)
       return V;
     if (auto *VC = dyn_cast<Constant>(V))
       return Insert(Folder.CreateFPCast(VC, DestTy), Name);
     return Insert(CastInst::CreateFPCast(V, DestTy), Name);
   }
 
+  CallInst *CreateConstrainedFPCast(
+      Intrinsic::ID ID, Value *V, Type *DestTy,
+      Instruction *FMFSource = nullptr, const Twine &Name = "",
+      MDNode *FPMathTag = nullptr,
+      Optional<ConstrainedFPIntrinsic::RoundingMode> Rounding = None,
+      Optional<ConstrainedFPIntrinsic::ExceptionBehavior> Except = None) {
+    Value *RoundingV = getConstrainedFPRounding(Rounding);
+    Value *ExceptV = getConstrainedFPExcept(Except);
+
+    FastMathFlags UseFMF = FMF;
+    if (FMFSource)
+      UseFMF = FMFSource->getFastMathFlags();
+
+    CallInst *C;
+    if (ID == Intrinsic::experimental_constrained_fpext)
+      C = CreateIntrinsic(ID, {DestTy, V->getType()}, {V, ExceptV}, nullptr,
+                          Name);
+    else
+      C = CreateIntrinsic(ID, {DestTy, V->getType()}, {V, RoundingV, ExceptV},
+                          nullptr, Name);
+    return cast<CallInst>(setFPAttrs(C, FPMathTag, UseFMF));
+  }
+
   // Provided to resolve 'CreateIntCast(Ptr, Ptr, "...")', giving a
   // compile time error, instead of converting the string to bool for the
   // isSigned parameter.
   Value *CreateIntCast(Value *, Type *, const char *) = delete;
 
   //===--------------------------------------------------------------------===//
   // Instruction creation methods: Compare Instructions
   //===--------------------------------------------------------------------===//

unittests/IR/IRBuilderTest.cpp

TEST_F(IRBuilderTest, Intrinsics) {
   EXPECT_EQ(II->getIntrinsicID(), Intrinsic::fma);
   EXPECT_TRUE(II->hasNoInfs());
   EXPECT_FALSE(II->hasNoNaNs());
 }
 
 TEST_F(IRBuilderTest, ConstrainedFP) {
   IRBuilder<> Builder(BB);
   Value *V;
+  Value *VDouble;
   CallInst *Call;
   IntrinsicInst *II;
+  GlobalVariable *GVDouble = new GlobalVariable(*M, Type::getDoubleTy(Ctx),
+                            true, GlobalValue::ExternalLinkage, nullptr);
 
   V = Builder.CreateLoad(GV->getValueType(), GV);
+  VDouble = Builder.CreateLoad(GVDouble->getValueType(), GVDouble);
 
   // See if we get constrained intrinsics instead of non-constrained
   // instructions.
   Builder.setIsFPConstrained(true);
 
   V = Builder.CreateFAdd(V, V);
   ASSERT_TRUE(isa<IntrinsicInst>(V));
   II = cast<IntrinsicInst>(V);
TEST_F(IRBuilderTest, ConstrainedFP) {
   II = cast<IntrinsicInst>(V);
   EXPECT_EQ(II->getIntrinsicID(), Intrinsic::experimental_constrained_fdiv);
   
   V = Builder.CreateFRem(V, V);
   ASSERT_TRUE(isa<IntrinsicInst>(V));
   II = cast<IntrinsicInst>(V);
   EXPECT_EQ(II->getIntrinsicID(), Intrinsic::experimental_constrained_frem);
 
+  V = Builder.CreateFPTrunc(VDouble, Type::getFloatTy(Ctx));
+  ASSERT_TRUE(isa<IntrinsicInst>(V));
+  II = cast<IntrinsicInst>(V);
+  EXPECT_EQ(II->getIntrinsicID(), Intrinsic::experimental_constrained_fptrunc);
+
+  VDouble = Builder.CreateFPExt(V, Type::getDoubleTy(Ctx));
+  ASSERT_TRUE(isa<IntrinsicInst>(VDouble));
+  II = cast<IntrinsicInst>(VDouble);
+  EXPECT_EQ(II->getIntrinsicID(), Intrinsic::experimental_constrained_fpext);
+
   // Verify the codepaths for setting and overriding the default metadata.
   V = Builder.CreateFAdd(V, V);
   ASSERT_TRUE(isa<ConstrainedFPIntrinsic>(V));
   auto *CII = cast<ConstrainedFPIntrinsic>(V);
   ASSERT_TRUE(CII->getExceptionBehavior() == ConstrainedFPIntrinsic::ebStrict);
   ASSERT_TRUE(CII->getRoundingMode() == ConstrainedFPIntrinsic::rmDynamic);
 
   Builder.setDefaultConstrainedExcept(ConstrainedFPIntrinsic::ebIgnore);