[analyzer] Add modelling of __builtin_assume

Differential Revision: https://reviews.llvm.org/D33092

llvm-svn: 302880

clang/lib/StaticAnalyzer/Checkers/BuiltinFunctionChecker.cpp

@@ -41,6 +41,22 @@ bool BuiltinFunctionChecker::evalCall(const CallExpr *CE,
   default:
     return false;
 
+  case Builtin::BI__builtin_assume: {
+    assert (CE->arg_begin() != CE->arg_end());
+    SVal ArgSVal = state->getSVal(CE->getArg(0), LCtx);
+    if (ArgSVal.isUndef())
+      return true; // Return true to model purity.
+
+    state = state->assume(ArgSVal.castAs<DefinedOrUnknownSVal>(), true);
+    // FIXME: do we want to warn here? Not right now. The most reports might
+    // come from infeasible paths, thus being false positives.
+    if (!state)
+      return true;
+
+    C.addTransition(state);
+    return true;
+  }
+
   case Builtin::BI__builtin_unpredictable:
   case Builtin::BI__builtin_expect:
   case Builtin::BI__builtin_assume_aligned:

clang/test/Analysis/builtin-assume.c

@@ -0,0 +1,8 @@
+// RUN: %clang_analyze_cc1 -analyzer-checker=core,debug.ExprInspection -verify %s
+
+void clang_analyzer_eval(int);
+
+void f(int i) {
+  __builtin_assume(i < 10);
+  clang_analyzer_eval(i < 15); // expected-warning {{TRUE}}
+}