[analyzer] Functions marked __attribute__((const)) don't modify any memory.

This applies to __attribute__((pure)) as well, but 'const' is more interesting
because many of our builtins are marked 'const'.

PR19661

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@208154 91177308-0d34-0410-b5e6-96231b3b80d8

lib/StaticAnalyzer/Core/CallEvent.cpp

@@ -139,6 +139,11 @@ ProgramStateRef CallEvent::invalidateRegions(unsigned BlockCount,
                                              ProgramStateRef Orig) const {
   ProgramStateRef Result = (Orig ? Orig : getState());
 
+  // Don't invalidate anything if the callee is marked pure/const.
+  if (const Decl *callee = getDecl())
+    if (callee->hasAttr<PureAttr>() || callee->hasAttr<ConstAttr>())
+      return Result;
+
   SmallVector<SVal, 8> ValuesToInvalidate;
   RegionAndSymbolInvalidationTraits ETraits;
 

test/Analysis/call-invalidation.cpp

@@ -89,3 +89,32 @@ void testConstReferenceStruct() {
   clang_analyzer_eval(x == 42); // expected-warning{{UNKNOWN}}
 }
 
+
+void usePointerPure(int * const *) __attribute__((pure));
+void usePointerConst(int * const *) __attribute__((const));
+
+void testPureConst() {
+  extern int global;
+  int x;
+  int *p;
+
+  p = &x;
+  x = 42;
+  global = -5;
+  clang_analyzer_eval(x == 42); // expected-warning{{TRUE}}
+  clang_analyzer_eval(global == -5); // expected-warning{{TRUE}}
+
+  usePointerPure(&p);
+  clang_analyzer_eval(x == 42); // expected-warning{{TRUE}}
+  clang_analyzer_eval(global == -5); // expected-warning{{TRUE}}
+
+  usePointerConst(&p);
+  clang_analyzer_eval(x == 42); // expected-warning{{TRUE}}
+  clang_analyzer_eval(global == -5); // expected-warning{{TRUE}}
+
+  usePointer(&p);
+  clang_analyzer_eval(x == 42); // expected-warning{{UNKNOWN}}
+  clang_analyzer_eval(global == -5); // expected-warning{{UNKNOWN}}
+}
+
+