r213266 - Add an __assume side-effects warning

[Hal Finkel]

Author: hfinkel
Date: Thu Jul 17 09:25:55 2014
New Revision: 213266

URL: http://llvm.org/viewvc/llvm-project?rev=213266&view=rev
Log:
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).

Added:
    cfe/trunk/test/Sema/builtin-assume.c
Modified:
    cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td
    cfe/trunk/include/clang/Sema/Sema.h
    cfe/trunk/lib/Sema/SemaChecking.cpp

Modified: cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td?rev=213266&r1=213265&r2=213266&view=diff
==============================================================================
--- cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td (original)
+++ cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td Thu Jul 17 09:25:55 2014
@@ -444,6 +444,10 @@ def note_strncat_wrong_size : Note<
   "change the argument to be the free space in the destination buffer minus " 
   "the terminating null byte">;
 
+def warn_assume_side_effects : Warning<
+  "the argument to __assume has side effects that will be discarded">,
+  InGroup<DiagGroup<"assume">>;
+
 /// main()
 // static main() is not an error in C, just in C++.
 def warn_static_main : Warning<"'main' should not be declared static">,

Modified: cfe/trunk/include/clang/Sema/Sema.h
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/include/clang/Sema/Sema.h?rev=213266&r1=213265&r2=213266&view=diff
==============================================================================
--- cfe/trunk/include/clang/Sema/Sema.h (original)
+++ cfe/trunk/include/clang/Sema/Sema.h Thu Jul 17 09:25:55 2014
@@ -8261,6 +8261,7 @@ public:
 
 private:
   bool SemaBuiltinPrefetch(CallExpr *TheCall);
+  bool SemaBuiltinAssume(CallExpr *TheCall);
   bool SemaBuiltinLongjmp(CallExpr *TheCall);
   ExprResult SemaBuiltinAtomicOverloaded(ExprResult TheCallResult);
   ExprResult SemaAtomicOpsOverloaded(ExprResult TheCallResult,

Modified: cfe/trunk/lib/Sema/SemaChecking.cpp
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Sema/SemaChecking.cpp?rev=213266&r1=213265&r2=213266&view=diff
==============================================================================
--- cfe/trunk/lib/Sema/SemaChecking.cpp (original)
+++ cfe/trunk/lib/Sema/SemaChecking.cpp Thu Jul 17 09:25:55 2014
@@ -175,6 +175,10 @@ Sema::CheckBuiltinFunctionCall(unsigned
     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();
@@ -1952,6 +1956,20 @@ bool Sema::SemaBuiltinPrefetch(CallExpr
 
   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.

Added: cfe/trunk/test/Sema/builtin-assume.c
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/Sema/builtin-assume.c?rev=213266&view=auto
==============================================================================
--- cfe/trunk/test/Sema/builtin-assume.c (added)
+++ cfe/trunk/test/Sema/builtin-assume.c Thu Jul 17 09:25:55 2014
@@ -0,0 +1,8 @@
+// RUN: %clang_cc1 -triple i386-mingw32 -fms-extensions -fsyntax-only -verify %s
+
+int foo(int *a, int i) {
+  __assume(i != 4);
+  __assume(++i > 2); //expected-warning {{the argument to __assume has side effects that will be discarded}}
+  return a[i];
+}
+