[clang] Fix crash when there is an invalid declaration with flag -Wcast-align

[qdelacru]

Summary

When there is unknown type in a struct in code compiled with -Wcast-align, the compiler crashes due to clang::ASTContext::getASTRecordLayout() failing an assert.

repro.c:1:21: error: unknown type name 'doesnotexist'
struct { int hello; doesnotexist world; } foo;
                    ^
clang: /root/llvm-project/clang/lib/AST/RecordLayoutBuilder.cpp:3230: const clang::ASTRecordLayout& clang::ASTContext::getASTRecordLayout(const clang::RecordDecl*) const: Assertion `!D->isInvalidDecl() && "Cannot get layout of invalid decl!"' failed.

Added check that the RecordDecl is valid before calling getASTRecordLayout()

[qdelacru]

Fix format

[aaron.ballman]

Thank you for the fix, LGTM! Do you need help landing the change? If so, please let me know what name and email address you'd like me to use for patch attribution.

[qdelacru]

Please use Queen Dela Cruz, [e-mail]. Thanks!

[aaron.ballman]

Thank you for the fix! I've applied in 3c5721d77275d2a7bdaeeadd0b1c3864f1166110

clang/lib/Sema/SemaChecking.cpp

if (auto *VD = dyn_cast<VarDecl>(cast<DeclRefExpr>(E)->getDecl())) {
       if (VD->hasInit())
         return getBaseAlignmentAndOffsetFromLValue(VD->getInit(), Ctx);
     }
     break;
   }
   case Stmt::MemberExprClass: {
     auto *ME = cast<MemberExpr>(E);
     auto *FD = dyn_cast<FieldDecl>(ME->getMemberDecl());
-    if (!FD || FD->getType()->isReferenceType())
+    if (!FD || FD->getType()->isReferenceType() || FD->getParent()->isInvalidDecl())
       break;
     Optional<std::pair<CharUnits, CharUnits>> P;
     if (ME->isArrow())
       P = getBaseAlignmentAndOffsetFromPtr(ME->getBase(), Ctx);
     else
       P = getBaseAlignmentAndOffsetFromLValue(ME->getBase(), Ctx);
     if (!P)
       break;

clang/test/Sema/warn-cast-align.c

 
 // No warnings.
 typedef int (*FnTy)(void);
 unsigned int func5(void);
 
 FnTy test5(void) {
   return (FnTy)&func5;
 }
+
+
+void test6() {
+    struct { int hello; doesnotexist world; } foo; // expected-error {{unknown type name 'doesnotexist'}}
+    void** repro = (void**)&foo.hello;             // expected-warning {{cast from 'int *' to 'void **' increases required alignment from 4 to 8}}             
+}