[PATCH] D24905: Fix unreachable code false positive, vardecl in switch

[Daniel Marjamäki via cfe-commits]

danielmarjamaki created this revision.
danielmarjamaki added subscribers: cfe-commits, NoQ, zaks.anna, a.sidorin, xazax.hun.
danielmarjamaki set the repository for this revision to rL LLVM.

This patch fixes false positives for vardecls that are technically unreachable but they are needed.
```
  switch (x) {
    int a;  // <- This is unreachable but needed
  case 1:
    a = ...
```


For this code there will be Wunused-variable:
```
  if (1+2==45) {
    int x;
  }
```

For this code there is 'unreachable code' warning on the 'if (1)':
```
  if (1+2==45) {
    int x;
    if (1) {}
  }  
```


Repository:
  rL LLVM

https://reviews.llvm.org/D24905

Files:
  lib/StaticAnalyzer/Checkers/UnreachableCodeChecker.cpp
  test/Analysis/unreachable-code-path.c

Index: test/Analysis/unreachable-code-path.c
===================================================================
--- test/Analysis/unreachable-code-path.c
+++ test/Analysis/unreachable-code-path.c
@@ -158,3 +158,16 @@
     }
   }
 }
+
+// don't warn about unreachable vardecl
+void varDecl() {
+  switch (x) {
+    int a; // No warning here.
+  case 1:
+    a=1;
+    break;
+  case 2:
+    a=2;
+    break;
+  }
+}
Index: lib/StaticAnalyzer/Checkers/UnreachableCodeChecker.cpp
===================================================================
--- lib/StaticAnalyzer/Checkers/UnreachableCodeChecker.cpp
+++ lib/StaticAnalyzer/Checkers/UnreachableCodeChecker.cpp
@@ -191,8 +191,10 @@
 // Find the Stmt* in a CFGBlock for reporting a warning
 const Stmt *UnreachableCodeChecker::getUnreachableStmt(const CFGBlock *CB) {
   for (CFGBlock::const_iterator I = CB->begin(), E = CB->end(); I != E; ++I) {
-    if (Optional<CFGStmt> S = I->getAs<CFGStmt>())
-      return S->getStmt();
+    if (Optional<CFGStmt> S = I->getAs<CFGStmt>()) {
+      if (isa<Expr>(S->getStmt()))
+        return S->getStmt();
+    }
   }
   if (const Stmt *S = CB->getTerminator())
     return S;


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