[PATCH] D99262: [analyzer] Fix dead store checker false positive

[Valeriy Savchenko via Phabricator via cfe-commits]

vsavchenko updated this revision to Diff 333793.
vsavchenko added a comment.

Add another test


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D99262/new/

https://reviews.llvm.org/D99262

Files:
  clang/lib/StaticAnalyzer/Checkers/DeadStoresChecker.cpp
  clang/test/Analysis/dead-stores.c


Index: clang/test/Analysis/dead-stores.c
===================================================================
--- clang/test/Analysis/dead-stores.c
+++ clang/test/Analysis/dead-stores.c
@@ -635,3 +635,27 @@
   volatile int v;
   v = 0; // no warning
 }
+
+struct Foo {
+  int x;
+  int y;
+};
+
+struct Foo rdar34122265_getFoo(void);
+
+int rdar34122265_test(int input) {
+  // This is allowed for defensive programming.
+  struct Foo foo = {0, 0};
+  if (input > 0) {
+    foo = rdar34122265_getFoo();
+  } else {
+    return 0;
+  }
+  return foo.x + foo.y;
+}
+
+void rdar34122265_test_cast() {
+  // This is allowed for defensive programming.
+  struct Foo foo = {0, 0};
+  (void)foo;
+}
Index: clang/lib/StaticAnalyzer/Checkers/DeadStoresChecker.cpp
===================================================================
--- clang/lib/StaticAnalyzer/Checkers/DeadStoresChecker.cpp
+++ clang/lib/StaticAnalyzer/Checkers/DeadStoresChecker.cpp
@@ -11,17 +11,18 @@
 //
 //===----------------------------------------------------------------------===//
 
-#include "clang/Lex/Lexer.h"
-#include "clang/StaticAnalyzer/Checkers/BuiltinCheckerRegistration.h"
 #include "clang/AST/ASTContext.h"
 #include "clang/AST/Attr.h"
 #include "clang/AST/ParentMap.h"
 #include "clang/AST/RecursiveASTVisitor.h"
 #include "clang/Analysis/Analyses/LiveVariables.h"
+#include "clang/Lex/Lexer.h"
+#include "clang/StaticAnalyzer/Checkers/BuiltinCheckerRegistration.h"
 #include "clang/StaticAnalyzer/Core/BugReporter/BugReporter.h"
 #include "clang/StaticAnalyzer/Core/Checker.h"
 #include "clang/StaticAnalyzer/Core/PathSensitive/AnalysisManager.h"
 #include "llvm/ADT/BitVector.h"
+#include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/SmallString.h"
 #include "llvm/Support/SaveAndRestore.h"
 
@@ -415,8 +416,23 @@
               if (E->isEvaluatable(Ctx))
                 return;
 
+              // We should also allow defensive initialization of structs.
+              if (const auto *ILE =
+                      dyn_cast<InitListExpr>(E->IgnoreParenCasts())) {
+                // We can use exactly the same logic here.
+                // If all fields of the struct are initialized with constants,
+                //
+                // e.g. : Foo x = { 0, 1 };
+                //
+                // we shouldn't complain about the fact that it is not used.
+                if (llvm::all_of(ILE->inits(), [this](const Expr *Init) {
+                      return Init->isEvaluatable(Ctx);
+                    }))
+                  return;
+              }
+
               if (const DeclRefExpr *DRE =
-                  dyn_cast<DeclRefExpr>(E->IgnoreParenCasts()))
+                      dyn_cast<DeclRefExpr>(E->IgnoreParenCasts()))
                 if (const VarDecl *VD = dyn_cast<VarDecl>(DRE->getDecl())) {
                   // Special case: check for initialization from constant
                   //  variables.


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