implement rdar://6091492 - ?: with __builtin_constant_p as the operand is an i-c-e.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@60934 91177308-0d34-0410-b5e6-96231b3b80d8

docs/InternalsManual.html

@@ -1152,7 +1152,10 @@ interacts with constant evaluation:</p>
     any evaluatable subexpression to be accepted as an integer constant
     expression.</li>
 <li><b><tt>__builtin_constant_p</tt></b>: This returns true (as a integer
-    constant expression) if the operand is any evaluatable constant.</li>
+    constant expression) if the operand is any evaluatable constant.  As a
+    special case, if <tt>__builtin_constant_p</tt> is the (potentially
+    parenthesized) condition of a conditional operator expression ("?:"), only
+    the true side of the conditional operator is considered.</li>
 <li><b><tt>__builtin_choose_expr</tt></b>: The condition is required to be an
     integer constant expression, but we accept any constant as an "extension of
     an extension".  This only evaluates one operand depending on which way the

lib/AST/Expr.cpp

@@ -1017,13 +1017,22 @@ bool Expr::isIntegerConstantExpr(llvm::APSInt &Result, ASTContext &Ctx,
   case ConditionalOperatorClass: {
     const ConditionalOperator *Exp = cast<ConditionalOperator>(this);
     
-    if (!Exp->getCond()->isIntegerConstantExpr(Result, Ctx, Loc, isEvaluated))
+    const Expr *Cond = Exp->getCond();
+    
+    if (!Cond->isIntegerConstantExpr(Result, Ctx, Loc, isEvaluated))
       return false;
     
     const Expr *TrueExp  = Exp->getLHS();
     const Expr *FalseExp = Exp->getRHS();
     if (Result == 0) std::swap(TrueExp, FalseExp);
     
+    // 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.
+    if (const CallExpr *CallCE = dyn_cast<CallExpr>(Cond->IgnoreParenCasts()))
+      if (CallCE->isBuiltinCall() == Builtin::BI__builtin_constant_p)
+        FalseExp = 0;
+    
     // Evaluate the false one first, discard the result.
     if (FalseExp && !FalseExp->isIntegerConstantExpr(Result, Ctx, Loc, false))
       return false;

test/Sema/i-c-e3.c

@@ -1,3 +1,8 @@
-// RUN: clang %s -fsyntax-only -verify
+// RUN: clang %s -fsyntax-only -verify -pedantic
 
 int a() {int p; *(1 ? &p : (void*)(0 && (a(),1))) = 10;}
+
+// rdar://6091492 - ?: with __builtin_constant_p as the operand is an i-c-e.
+int expr;
+char w[__builtin_constant_p(expr) ? expr : 1];
+