[Clang] Reland '__has_builtin should return false for aux triple builtins' (#126324)

Reland #121839 based on the
results of the Discourse discussion
[here](https://discourse.llvm.org/t/rfc-has-builtin-behavior-on-offloading-targets/84964).

---------

Signed-off-by: Sarnie, Nick <[email protected]>

Author: sarnex

clang/docs/LanguageExtensions.rst

@@ -68,6 +68,9 @@ It can be used like this:
   ``__has_builtin`` should not be used to detect support for a builtin macro;
   use ``#ifdef`` instead.
 
+  When compiling with target offloading, ``__has_builtin`` only considers the
+  currently active target.
+
 ``__has_constexpr_builtin``
 ---------------------------
 

clang/docs/ReleaseNotes.rst

@@ -37,6 +37,8 @@ Potentially Breaking Changes
 C/C++ Language Potentially Breaking Changes
 -------------------------------------------
 
+- The ``__has_builtin`` function now only considers the currently active target when being used with target offloading.
+
 C++ Specific Potentially Breaking Changes
 -----------------------------------------
 - For C++20 modules, the Reduced BMI mode will be the default option. This may introduce

clang/lib/Lex/PPMacroExpansion.cpp

@@ -1760,7 +1760,8 @@ void Preprocessor::ExpandBuiltinMacro(Token &Tok) {
               Tok, *this, diag::err_feature_check_malformed);
           if (!II)
             return false;
-          else if (II->getBuiltinID() != 0) {
+          unsigned BuiltinID = II->getBuiltinID();
+          if (BuiltinID != 0) {
             switch (II->getBuiltinID()) {
             case Builtin::BI__builtin_cpu_is:
               return getTargetInfo().supportsCpuIs();
@@ -1774,8 +1775,11 @@ void Preprocessor::ExpandBuiltinMacro(Token &Tok) {
               // usual allocation and deallocation functions. Required by libc++
               return 201802;
             default:
+              // __has_builtin should return false for aux builtins.
+              if (getBuiltinInfo().isAuxBuiltinID(BuiltinID))
+                return false;
               return Builtin::evaluateRequiredTargetFeatures(
-                  getBuiltinInfo().getRequiredFeatures(II->getBuiltinID()),
+                  getBuiltinInfo().getRequiredFeatures(BuiltinID),
                   getTargetInfo().getTargetOpts().FeatureMap);
             }
             return true;

clang/test/Headers/__cpuidex_conflict.c

@@ -3,7 +3,10 @@
 // RUN: %clang_cc1 %s -ffreestanding -fms-extensions -fms-compatibility \
 // RUN:  -fms-compatibility-version=19.00 -triple x86_64-pc-windows-msvc -emit-llvm -o -
 // %clang_cc1 %s -ffreestanding -triple x86_64-w64-windows-gnu -fms-extensions -emit-llvm -o -
-// RUN: %clang_cc1 %s -ffreestanding -fopenmp -fopenmp-is-target-device -aux-triple x86_64-unknown-linux-gnu
+//
+// FIXME: See https://github.com/llvm/llvm-project/pull/121839 and
+// FIXME: https://github.com/llvm/llvm-project/pull/126324
+// RUN: not %clang_cc1 %s -ffreestanding -fopenmp -fopenmp-is-target-device -aux-triple x86_64-unknown-linux-gnu
 
 typedef __SIZE_TYPE__ size_t;
 

clang/test/Preprocessor/builtin_aux_info.cpp

@@ -0,0 +1,18 @@
+// RUN: %clang_cc1 -fopenmp -triple=spirv64 -fopenmp-is-target-device \
+// RUN: -aux-triple x86_64-linux-unknown -E %s | FileCheck -implicit-check-not=BAD %s
+
+// RUN: %clang_cc1 -fopenmp -triple=nvptx64 -fopenmp-is-target-device \
+// RUN: -aux-triple x86_64-linux-unknown -E %s | FileCheck -implicit-check-not=BAD %s
+
+// RUN: %clang_cc1 -fopenmp -triple=amdgcn-amd-amdhsa -fopenmp-is-target-device \
+// RUN: -aux-triple x86_64-linux-unknown -E %s | FileCheck -implicit-check-not=BAD %s
+
+// RUN: %clang_cc1 -fopenmp -triple=aarch64 -fopenmp-is-target-device \
+// RUN: -aux-triple x86_64-linux-unknown -E %s | FileCheck -implicit-check-not=BAD %s
+
+// CHECK: GOOD
+#if __has_builtin(__builtin_ia32_pause)
+  BAD
+#else
+  GOOD
+#endif