[clang] [BPF] make __BPF_FEATURE_MAY_GOTO available for cpuv1 (PR #108071)

[via cfe-commits]

https://github.com/eddyz87 created https://github.com/llvm/llvm-project/pull/108071

For some reason `__BPF_FEATURE_MAY_GOTO` is available for CPUs v{2,3,4} but is not available for CPU v1. This limitation is arbitrary:
- the instruction is never produced by LLVM backend;
- on Linux Kernel side this instruction is available in kernels that also support CPUv4.

Hence, it is more consistent to either always allow `__BPF_FEATURE_MAY_GOTO` or only allow it for CPUv4.

>From 170f6a604b041bb33c5089dd84fd26de7bd2292e Mon Sep 17 00:00:00 2001
From: Eduard Zingerman <eddyz87 at gmail.com>
Date: Tue, 10 Sep 2024 11:11:58 -0700
Subject: [PATCH] [BPF] make __BPF_FEATURE_MAY_GOTO available for cpuv1

For some reason __BPF_FEATURE_MAY_GOTO is available for CPUs v{2,3,4}
but is not available for CPU v1. This limitation is arbitrary:
- the instruction is never produced by LLVM backend;
- on Linux Kernel side this instruction is available in kernels that
  also support CPUv4.

Hence, it is more consistent to either always allow
__BPF_FEATURE_MAY_GOTO or only allow it for CPUv4.
---
 clang/lib/Basic/Targets/BPF.cpp | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/clang/lib/Basic/Targets/BPF.cpp b/clang/lib/Basic/Targets/BPF.cpp
index a94ceee5a6a5e7..931f407ecb0d7e 100644
--- a/clang/lib/Basic/Targets/BPF.cpp
+++ b/clang/lib/Basic/Targets/BPF.cpp
@@ -37,6 +37,7 @@ void BPFTargetInfo::getTargetDefines(const LangOptions &Opts,
   }
 
   Builder.defineMacro("__BPF_FEATURE_ADDR_SPACE_CAST");
+  Builder.defineMacro("__BPF_FEATURE_MAY_GOTO");
 
   if (CPU.empty())
     CPU = "v3";
@@ -48,7 +49,6 @@ void BPFTargetInfo::getTargetDefines(const LangOptions &Opts,
 
   std::string CpuVerNumStr = CPU.substr(1);
   Builder.defineMacro("__BPF_CPU_VERSION__", CpuVerNumStr);
-  Builder.defineMacro("__BPF_FEATURE_MAY_GOTO");
 
   int CpuVerNum = std::stoi(CpuVerNumStr);
   if (CpuVerNum >= 2)