Implement the final (hopefully) wrinkle to i-c-e + builtin_constant_p

processing: it allows arbitrary foldable constants as the operand of ?: when
builtin_constant_p is the condition.

llvm-svn: 60954

1 files changed, 11 insertions, 7 deletions

diff --git a/clang/lib/AST/Expr.cpp b/clang/lib/AST/Expr.cpp
index bdc5096584a..c01c973cf59 100644
--- a/clang/lib/AST/Expr.cpp
+++ b/clang/lib/AST/Expr.cpp
@@ -1028,14 +1028,18 @@ bool Expr::isIntegerConstantExpr(llvm::APSInt &Result, ASTContext &Ctx,
     
     // If the condition (ignoring parens) is a __builtin_constant_p call, 
     // then only the true side is actually considered in an integer constant
-    // expression.  This is an important GNU extension.
-    //
-    // FIXME: ?: with a conditional expr should arguably be an i-c-e if the true
-    // side can be folded in any way to a constant.  See GCC PR38377 for
-    // discussion.
+    // expression, and it is fully evaluated.  This is an important GNU
+    // extension.  See GCC PR38377 for discussion.
     if (const CallExpr *CallCE = dyn_cast<CallExpr>(Cond->IgnoreParenCasts()))
-      if (CallCE->isBuiltinCall() == Builtin::BI__builtin_constant_p)
-        FalseExp = 0;
+      if (CallCE->isBuiltinCall() == Builtin::BI__builtin_constant_p) {
+        EvalResult EVResult;
+        if (!Evaluate(EVResult, Ctx) || EVResult.HasSideEffects)
+          return false;
+        assert(EVResult.Val.isInt() && "FP conditional expr not expected");
+        Result = EVResult.Val.getInt();
+        if (Loc) *Loc = EVResult.DiagLoc;
+        return true;
+      }
     
     // Evaluate the false one first, discard the result.
     if (FalseExp && !FalseExp->isIntegerConstantExpr(Result, Ctx, Loc, false))