Add an __assume side-effects warning

In MS-compatibility mode, we support the __assume builtin. The __assume builtin
does not evaluate its arguments, and we should issue a warning if __assume is
provided with an argument with side effects (because these effects will be
discarded).

This is similar in spirit to the warnings issued by other compilers (Intel
Diagnostic 2261, MS Compiler Warning C4557).

llvm-svn: 213266

1 files changed, 18 insertions, 0 deletions

diff --git a/clang/lib/Sema/SemaChecking.cpp b/clang/lib/Sema/SemaChecking.cpp
index 7a23797d477..d8b801bf0a6 100644
--- a/clang/lib/Sema/SemaChecking.cpp
+++ b/clang/lib/Sema/SemaChecking.cpp
@@ -175,6 +175,10 @@ Sema::CheckBuiltinFunctionCall(unsigned BuiltinID, CallExpr *TheCall) {
     if (SemaBuiltinPrefetch(TheCall))
       return ExprError();
     break;
+  case Builtin::BI__assume:
+    if (SemaBuiltinAssume(TheCall))
+      return ExprError();
+    break;
   case Builtin::BI__builtin_object_size:
     if (SemaBuiltinConstantArgRange(TheCall, 1, 0, 3))
       return ExprError();
@@ -1953,6 +1957,20 @@ bool Sema::SemaBuiltinPrefetch(CallExpr *TheCall) {
   return false;
 }
 
+/// SemaBuiltinAssume - Handle __assume (MS Extension).
+// __assume does not evaluate its arguments, and should warn if its argument
+// has side effects.
+bool Sema::SemaBuiltinAssume(CallExpr *TheCall) {
+  Expr *Arg = TheCall->getArg(0);
+  if (Arg->isInstantiationDependent()) return false;
+
+  if (Arg->HasSideEffects(Context))
+    return Diag(Arg->getLocStart(), diag::warn_assume_side_effects)
+      << Arg->getSourceRange();
+
+  return false;
+}
+
 /// SemaBuiltinConstantArg - Handle a check if argument ArgNum of CallExpr
 /// TheCall is a constant expression.
 bool Sema::SemaBuiltinConstantArg(CallExpr *TheCall, int ArgNum,