Explicit cast on customized offsetof should not be ignored when evaluating as const

[danix800]

Summary

If ignored, the subexpr is a UnaryOperator (&) which cannot be evaluated (assertion failed).

#define offsetof(type,memb) ((unsigned long)&((type*)0)->memb)

[steakhal]

I love it. Short, to the point. Thanks.
I think this is the right way to fix this.
Good job.
Can you merge the change? Or should I do it on you behalf?

[danix800]

In D144780#4154487, @steakhal wrote:

I love it. Short, to the point. Thanks.
I think this is the right way to fix this.
Good job.
Can you merge the change? Or should I do it on you behalf?

I've no permission to merge, please do it for me. Thanks!

[steakhal]

In D144780#4154619, @danix800 wrote:

In D144780#4154487, @steakhal wrote:

I love it. Short, to the point. Thanks.
I think this is the right way to fix this.
Good job.
Can you merge the change? Or should I do it on you behalf?

I've no permission to merge, please do it for me. Thanks!

In that case please tell me what should I set as the commit-author?

[danix800]

danix800 ([e-mail]) is OK, thanks!

[steakhal]

Ah sorry that it took me so long to push this. I completely forgot about this one.

[steakhal]

As this resolves a crash, I'm backporting it: https://github.com/llvm/llvm-project/issues/61245

clang/lib/StaticAnalyzer/Core/BugReporter.cpp

if (const Stmt *S = Dst->getLabel()) {
     case Stmt::DefaultStmtClass:
       os << "Control jumps to the 'default' case at line "
         << End.asLocation().getExpansionLineNumber();
       break;
 
     case Stmt::CaseStmtClass: {
       os << "Control jumps to 'case ";
       const auto *Case = cast<CaseStmt>(S);
-      const Expr *LHS = Case->getLHS()->IgnoreParenCasts();
+      const Expr *LHS = Case->getLHS()->IgnoreParenImpCasts();
 
       // Determine if it is an enum.
       bool GetRawInt = true;
 
       if (const auto *DR = dyn_cast<DeclRefExpr>(LHS)) {
         // FIXME: Maybe this should be an assertion.  Are there cases
         // were it is not an EnumConstantDecl?
         const auto *D = dyn_cast<EnumConstantDecl>(DR->getDecl());

clang/test/Analysis/bitwise-ops-nocrash.c

+// RUN: %clang_analyze_cc1 -analyzer-checker=core -analyzer-output=text -triple x86_64-linux-gnu -Wno-shift-count-overflow -verify %s
+
+#define offsetof(type,memb) ((unsigned long)&((type*)0)->memb)
+
+typedef struct {
+  unsigned long guest_counter;
+  unsigned int guest_fpc;
+} S;
+
+// no crash
+int left_shift_overflow_no_crash(unsigned int i) {
+  unsigned shift = 323U; // expected-note{{'shift' initialized to 323}}
+  switch (i) { // expected-note{{Control jumps to 'case 8:'  at line 14}}
+  case offsetof(S, guest_fpc):
+    return 3 << shift; // expected-warning{{The result of the left shift is undefined due to shifting by '323', which is greater or equal to the width of type 'int'}}
+    // expected-note@-1{{The result of the left shift is undefined due to shifting by '323', which is greater or equal to the width of type 'int'}}
+  default:
+    break;
+  }
+
+  return 0;
+}