[BPF] do not generate predefined macro bpf

[yonghong-song]

Summary

"DefineStd(Builder, "bpf", Opts)" generates the following three macros:

bpf
__bpf
__bpf__

and the macro "bpf" is due to the fact that the target language
is C which allows GNU extensions.

The name "bpf" could be easily used as variable name or type
field name. For example, in current linux kernel, there are
four places where bpf is used as a field name. If the corresponding
types are included in bpf program, the compilation error will
occur.

This patch removed predefined macro "bpf" as well as "__bpf" which

is rarely used if used at all.

[ast]

lib/Basic/Targets/BPF.cpp

23

I don't think anyone is using this one.
May be we can keep __bpf__ and __BPF__ only?

[yonghong-song]

lib/Basic/Targets/BPF.cpp

23

We can do this for sure.

[yonghong-song]

remove __bpf.

[ast]

lib/Basic/Targets/BPF.cpp

 #include "clang/Basic/MacroBuilder.h"
 #include "llvm/ADT/StringRef.h"
 
 using namespace clang;
 using namespace clang::targets;
 
 void BPFTargetInfo::getTargetDefines(const LangOptions &Opts,
                                      MacroBuilder &Builder) const {
-  DefineStd(Builder, "bpf", Opts);
+  Builder.defineMacro("__bpf__");
   Builder.defineMacro("__BPF__");
 }
 
 static constexpr llvm::StringLiteral ValidCPUNames[] = {"generic", "v1", "v2",
                                                         "v3", "probe"};
 
 bool BPFTargetInfo::isValidCPUName(StringRef Name) const {
   return llvm::find(ValidCPUNames, Name) != std::end(ValidCPUNames);
 }
 
 void BPFTargetInfo::fillValidCPUList(SmallVectorImpl<StringRef> &Values) const {
   Values.append(std::begin(ValidCPUNames), std::end(ValidCPUNames));
 }

test/Preprocessor/bpf-predefined-macros.c

+// RUN: %clang -E -target bpfel -x c -o - %s | FileCheck %s
+// RUN: %clang -E -target bpfeb -x c -o - %s | FileCheck %s
+
+#ifdef __bpf__
+int b;
+#endif
+#ifdef __BPF__
+int c;
+#endif
+#ifdef bpf
+int d;
+#endif
+
+// CHECK: int b;
+// CHECK: int c;
+// CHECK-NOT: int d;