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/Serialization/ASTReaderStmt.cpp b/clang/lib/Serialization/ASTReaderStmt.cpp
index 6a4482b..a12fb8c 100644
--- a/clang/lib/Serialization/ASTReaderStmt.cpp
+++ b/clang/lib/Serialization/ASTReaderStmt.cpp
@@ -670,7 +670,7 @@
   E->setRHS(Record.readSubExpr());
   E->setOpcode((BinaryOperator::Opcode)Record.readInt());
   E->setOperatorLoc(ReadSourceLocation());
-  E->setFPContractable((bool)Record.readInt());
+  E->setFPFeatures(FPOptions(Record.readInt()));
 }
 
 void ASTStmtReader::VisitCompoundAssignOperator(CompoundAssignOperator *E) {
@@ -1225,7 +1225,7 @@
   VisitCallExpr(E);
   E->Operator = (OverloadedOperatorKind)Record.readInt();
   E->Range = Record.readSourceRange();
-  E->setFPContractable((bool)Record.readInt());
+  E->setFPFeatures(FPOptions(Record.readInt()));
 }
 
 void ASTStmtReader::VisitCXXConstructExpr(CXXConstructExpr *E) {