Encapsulate FPOptions and use it consistently

Sema holds the current FPOptions which is adjusted by 'pragma STDC
FP_CONTRACT'.  This then gets propagated into expression nodes as they are
built.

This encapsulates FPOptions so that this propagation happens opaquely rather
than directly with the fp_contractable on/off bit.  This allows controlled
transitioning of fp_contractable to a ternary value (off, on, fast).  It will
also allow adding more fast-math flags later.

This is toward moving fp-contraction=fast from an LLVM TargetOption to a
FastMathFlag in order to fix PR25721.

Differential Revision: https://reviews.llvm.org/D31166

llvm-svn: 298877
diff --git a/clang/lib/CodeGen/CGExprScalar.cpp b/clang/lib/CodeGen/CGExprScalar.cpp
index 4e17f36..9eb21b8 100644
--- a/clang/lib/CodeGen/CGExprScalar.cpp
+++ b/clang/lib/CodeGen/CGExprScalar.cpp
@@ -49,7 +49,7 @@
   Value *RHS;
   QualType Ty;  // Computation Type.
   BinaryOperator::Opcode Opcode; // Opcode of BinOp to perform
-  bool FPContractable;
+  FPOptions FPFeatures;
   const Expr *E;      // Entire expr, for error unsupported.  May not be binop.
 };
 
@@ -1718,7 +1718,7 @@
   BinOp.RHS = llvm::ConstantInt::get(InVal->getType(), 1, false);
   BinOp.Ty = E->getType();
   BinOp.Opcode = IsInc ? BO_Add : BO_Sub;
-  BinOp.FPContractable = false;
+  // FIXME: once UnaryOperator carries FPFeatures, copy it here.
   BinOp.E = E;
   return BinOp;
 }
@@ -1984,7 +1984,7 @@
     BinOp.LHS = llvm::Constant::getNullValue(BinOp.RHS->getType());
   BinOp.Ty = E->getType();
   BinOp.Opcode = BO_Sub;
-  BinOp.FPContractable = false;
+  // FIXME: once UnaryOperator carries FPFeatures, copy it here.
   BinOp.E = E;
   return EmitSub(BinOp);
 }
@@ -2205,7 +2205,7 @@
   Result.RHS = Visit(E->getRHS());
   Result.Ty  = E->getType();
   Result.Opcode = E->getOpcode();
-  Result.FPContractable = E->isFPContractable();
+  Result.FPFeatures = E->getFPFeatures();
   Result.E = E;
   return Result;
 }
@@ -2225,7 +2225,7 @@
   OpInfo.RHS = Visit(E->getRHS());
   OpInfo.Ty = E->getComputationResultType();
   OpInfo.Opcode = E->getOpcode();
-  OpInfo.FPContractable = E->isFPContractable();
+  OpInfo.FPFeatures = E->getFPFeatures();
   OpInfo.E = E;
   // Load/convert the LHS.
   LValue LHSLV = EmitCheckedLValue(E->getLHS(), CodeGenFunction::TCK_Store);
@@ -2672,7 +2672,7 @@
          "Only fadd/fsub can be the root of an fmuladd.");
 
   // Check whether this op is marked as fusable.
-  if (!op.FPContractable)
+  if (!op.FPFeatures.isFPContractable())
     return nullptr;
 
   // Check whether -ffp-contract=on. (If -ffp-contract=off/fast, fusing is