alpha.core.UnreachableCode - don't warn about unreachable code inside macro

[danielmarjamaki]

Summary

This patch fixes false positives for such code:

#define RETURN(X)  do { return; } while (0)

void dostuff(void) {
  RETURN(1); // no-warning
}

The condition "0" in the macro is unreachable but that condition is there for a good reason.

[zaks.anna]

We should pattern match for this specific macro pattern (ex: do{...}while(0) ) instead of suppressing all warnings coming from macros. Maybe we could use the same heuristic as -Wunreachable-code-return compiler warning?

[danielmarjamaki]

make pattern to avoid warnings more specific

[zaks.anna]

LGTM. Thank you!

cfe/trunk/lib/StaticAnalyzer/Checkers/UnreachableCodeChecker.cpp

if (!CB->empty()) {
         continue;
     }
 
     // We found a block that wasn't covered - find the statement to report
     SourceRange SR;
     PathDiagnosticLocation DL;
     SourceLocation SL;
     if (const Stmt *S = getUnreachableStmt(CB)) {
+      // In macros, 'do {...} while (0)' is often used. Don't warn about the
+      // condition 0 when it is unreachable.
+      if (S->getLocStart().isMacroID())
+        if (const auto *I = dyn_cast<IntegerLiteral>(S))
+          if (I->getValue() == 0ULL)
+            if (const Stmt *Parent = PM->getParent(S))
+              if (isa<DoStmt>(Parent))
+                continue;
       SR = S->getSourceRange();
       DL = PathDiagnosticLocation::createBegin(S, B.getSourceManager(), LC);
       SL = DL.asLocation();
       if (SR.isInvalid() || !SL.isValid())
         continue;
     }
     else
       continue;

cfe/trunk/test/Analysis/unreachable-code-path.c

static int inlineFunction(const int i) {
   if (table[i] != 0)
     return 1;
   return 0;
 }
 void test13(int i) {
   int x = inlineFunction(i);
   x && x < 10; // no-warning
 }
+
+// Don't warn in a macro
+#define RETURN(X)  do { return; } while (0)
+void macro(void) {
+  RETURN(1); // no-warning
+}
+