[clang] Add storage for APValue in ConstantExpr

Summary:
When using ConstantExpr we often need the result of the expression to be kept in the AST. Currently this is done on a by the node that needs the result and has been done multiple times for enumerator, for constexpr variables... . This patch adds to ConstantExpr the ability to store the result of evaluating the expression. no functional changes expected.

Changes:
 - Add trailling object to ConstantExpr that can hold an APValue or an uint64_t. the uint64_t is here because most ConstantExpr yield integral values so there is an optimized layout for integral values.
 - Add basic* serialization support for the trailing result.
 - Move conversion functions from an enum to a fltSemantics from clang::FloatingLiteral to llvm::APFloatBase. this change is to make it usable for serializing APValues.
 - Add basic* Import support for the trailing result.
 - ConstantExpr created in CheckConvertedConstantExpression now stores the result in the ConstantExpr Node.
 - Adapt AST dump to print the result when present.

basic* : None, Indeterminate, Int, Float, FixedPoint, ComplexInt, ComplexFloat,
the result is not yet used anywhere but for -ast-dump.

Reviewers: rsmith, martong, shafik

Reviewed By: rsmith

Subscribers: rnkovacs, hiraditya, dexonsmith, cfe-commits, llvm-commits

Tags: #clang, #llvm

Differential Revision: https://reviews.llvm.org/D62399

llvm-svn: 363493
diff --git a/clang/lib/Serialization/ASTReaderStmt.cpp b/clang/lib/Serialization/ASTReaderStmt.cpp
index 4955343..e94a912 100644
--- a/clang/lib/Serialization/ASTReaderStmt.cpp
+++ b/clang/lib/Serialization/ASTReaderStmt.cpp
@@ -533,6 +533,18 @@
 
 void ASTStmtReader::VisitConstantExpr(ConstantExpr *E) {
   VisitExpr(E);
+  E->ConstantExprBits.ResultKind = Record.readInt();
+  switch (E->ConstantExprBits.ResultKind) {
+  case ConstantExpr::RSK_Int64: {
+    E->Int64Result() = Record.readInt();
+    uint64_t tmp = Record.readInt();
+    E->ConstantExprBits.IsUnsigned = tmp & 0x1;
+    E->ConstantExprBits.BitWidth = tmp >> 1;
+    break;
+  }
+  case ConstantExpr::RSK_APValue:
+    E->APValueResult() = Record.readAPValue();
+  }
   E->setSubExpr(Record.readSubExpr());
 }
 
@@ -590,7 +602,8 @@
 
 void ASTStmtReader::VisitFloatingLiteral(FloatingLiteral *E) {
   VisitExpr(E);
-  E->setRawSemantics(static_cast<Stmt::APFloatSemantics>(Record.readInt()));
+  E->setRawSemantics(
+      static_cast<llvm::APFloatBase::Semantics>(Record.readInt()));
   E->setExact(Record.readInt());
   E->setValue(Record.getContext(), Record.readAPFloat(E->getSemantics()));
   E->setLocation(ReadSourceLocation());
@@ -2510,7 +2523,11 @@
       break;
 
     case EXPR_CONSTANT:
-      S = new (Context) ConstantExpr(Empty);
+      S = ConstantExpr::CreateEmpty(
+          Context,
+          static_cast<ConstantExpr::ResultStorageKind>(
+              Record[ASTStmtReader::NumExprFields]),
+          Empty);
       break;
 
     case EXPR_PREDEFINED: