[FPEnv] Teach the IRBuilder about correct use of the strictfp attribute.

The IRBuilder needs to add the strictfp attribute to function
definitions and calls when constrained floating point is enabled.

Since so far all front ends have had to do is flip the constrained
switch, I've made this patch always add the required attributes
when said constrained switch is enabled. This continues to keep
changes to front ends minimal.

Differential Revision: D69312

Author: kpneal

llvm/include/llvm/IR/IRBuilder.h

@@ -255,6 +255,21 @@ class IRBuilderBase {
     return DefaultConstrainedRounding;
   }
 
+  void setConstrainedFPFunctionAttr() {
+    assert(BB && "Must have a basic block to set any function attributes!");
+
+    Function *F = BB->getParent();
+    if (!F->hasFnAttribute(Attribute::StrictFP)) {
+      F->addFnAttr(Attribute::StrictFP);
+    }
+  }
+
+  void setConstrainedFPCallAttr(CallInst *I) {
+    if (!I->hasFnAttr(Attribute::StrictFP))
+      I->addAttribute(AttributeList::FunctionIndex, Attribute::StrictFP);
+    setConstrainedFPFunctionAttr();
+  }
+
   //===--------------------------------------------------------------------===//
   // RAII helpers.
   //===--------------------------------------------------------------------===//
@@ -1479,6 +1494,7 @@ class IRBuilder : public IRBuilderBase, public Inserter {
 
     CallInst *C = CreateIntrinsic(ID, {L->getType()},
                                   {L, R, RoundingV, ExceptV}, nullptr, Name);
+    setConstrainedFPCallAttr(C);
     setFPAttrs(C, FPMathTag, UseFMF);
     return C;
   }
@@ -2084,6 +2100,8 @@ class IRBuilder : public IRBuilderBase, public Inserter {
                           Name);
       break;
     }
+    setConstrainedFPCallAttr(C);
+
     if (isa<FPMathOperator>(C))
       setFPAttrs(C, FPMathTag, UseFMF);
     return C;
@@ -2240,6 +2258,8 @@ class IRBuilder : public IRBuilderBase, public Inserter {
                        ArrayRef<Value *> Args = None, const Twine &Name = "",
                        MDNode *FPMathTag = nullptr) {
     CallInst *CI = CallInst::Create(FTy, Callee, Args, DefaultOperandBundles);
+    if (IsFPConstrained)
+      setConstrainedFPCallAttr(CI);
     if (isa<FPMathOperator>(CI))
       setFPAttrs(CI, FPMathTag, FMF);
     return Insert(CI, Name);
@@ -2249,6 +2269,8 @@ class IRBuilder : public IRBuilderBase, public Inserter {
                        ArrayRef<OperandBundleDef> OpBundles,
                        const Twine &Name = "", MDNode *FPMathTag = nullptr) {
     CallInst *CI = CallInst::Create(FTy, Callee, Args, OpBundles);
+    if (IsFPConstrained)
+      setConstrainedFPCallAttr(CI);
     if (isa<FPMathOperator>(CI))
       setFPAttrs(CI, FPMathTag, FMF);
     return Insert(CI, Name);

llvm/unittests/IR/IRBuilderTest.cpp

@@ -229,6 +229,15 @@ TEST_F(IRBuilderTest, ConstrainedFP) {
   II = cast<IntrinsicInst>(VDouble);
   EXPECT_EQ(II->getIntrinsicID(), Intrinsic::experimental_constrained_fpext);
 
+  // Verify attributes on the call are created automatically.
+  AttributeSet CallAttrs = II->getAttributes().getFnAttributes();
+  EXPECT_EQ(CallAttrs.hasAttribute(Attribute::StrictFP), true);
+
+  // Verify attributes on the containing function are created automatically.
+  AttributeList Attrs = BB->getParent()->getAttributes();
+  AttributeSet FnAttrs = Attrs.getFnAttributes();
+  EXPECT_EQ(FnAttrs.hasAttribute(Attribute::StrictFP), true);
+
   // Verify the codepaths for setting and overriding the default metadata.
   V = Builder.CreateFAdd(V, V);
   ASSERT_TRUE(isa<ConstrainedFPIntrinsic>(V));