BPF: fix enum value 0 issue for __builtin_preserve_enum_value()

Lorenz Bauer reported that the following code will have
compilation error for bpf target:
    enum e { TWO };
    bpf_core_enum_value_exists(enum e, TWO);
The clang emitted the following error message:
    __builtin_preserve_enum_value argument 1 invalid

In SemaChecking, an expression like "*(enum NAME)1" will have
cast kind CK_IntegralToPointer, but "*(enum NAME)0" will have
cast kind CK_NullToPointer. Current implementation only permits
CK_IntegralToPointer, missing enum value 0 case.

This patch permits CK_NullToPointer cast kind and
the above test case can pass now.

Differential Revision: https://reviews.llvm.org/D97659

1 files changed, 4 insertions, 1 deletions

diff --git a/clang/lib/Sema/SemaChecking.cpp b/clang/lib/Sema/SemaChecking.cpp
index f67cba1..ccde2f3 100644
--- a/clang/lib/Sema/SemaChecking.cpp
+++ b/clang/lib/Sema/SemaChecking.cpp
@@ -2626,7 +2626,10 @@ static bool isValidBPFPreserveEnumValueArg(Expr *Arg) {
     return false;
 
   const auto *CE = dyn_cast<CStyleCastExpr>(UO->getSubExpr());
-  if (!CE || CE->getCastKind() != CK_IntegralToPointer)
+  if (!CE)
+    return false;
+  if (CE->getCastKind() != CK_IntegralToPointer &&
+      CE->getCastKind() != CK_NullToPointer)
     return false;
 
   // The integer must be from an EnumConstantDecl.