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

[Nick Sarnie via cfe-commits]

https://github.com/sarnex updated https://github.com/llvm/llvm-project/pull/126324

>From 894307419c0e1f001f4369a1e4fc2a11cf2e00ef Mon Sep 17 00:00:00 2001
From: "Sarnie, Nick" <nick.sarnie at intel.com>
Date: Mon, 28 Jul 2025 07:37:01 -0700
Subject: [PATCH 1/3] [clang] Reland '__has_builtin should return false for aux
 triple builtins'

Signed-off-by: Sarnie, Nick <nick.sarnie at intel.com>
---
 clang/lib/Lex/PPMacroExpansion.cpp           |  8 ++++++--
 clang/test/Headers/__cpuidex_conflict.c      |  5 ++++-
 clang/test/Preprocessor/builtin_aux_info.cpp | 18 ++++++++++++++++++
 3 files changed, 28 insertions(+), 3 deletions(-)
 create mode 100644 clang/test/Preprocessor/builtin_aux_info.cpp

diff --git a/clang/lib/Lex/PPMacroExpansion.cpp b/clang/lib/Lex/PPMacroExpansion.cpp
index 890567cfd3246..63c48e665ae32 100644
--- a/clang/lib/Lex/PPMacroExpansion.cpp
+++ b/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) {
+          auto 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;
diff --git a/clang/test/Headers/__cpuidex_conflict.c b/clang/test/Headers/__cpuidex_conflict.c
index 8687a6aa2f897..49795c447f6e0 100644
--- a/clang/test/Headers/__cpuidex_conflict.c
+++ b/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;
 
diff --git a/clang/test/Preprocessor/builtin_aux_info.cpp b/clang/test/Preprocessor/builtin_aux_info.cpp
new file mode 100644
index 0000000000000..60c8c6c492479
--- /dev/null
+++ b/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

>From b1d1b20fe534993b361363a7faff4d1dfdc07dfb Mon Sep 17 00:00:00 2001
From: "Sarnie, Nick" <nick.sarnie at intel.com>
Date: Mon, 28 Jul 2025 07:39:51 -0700
Subject: [PATCH 2/3] missed feedback

Signed-off-by: Sarnie, Nick <nick.sarnie at intel.com>
---
 clang/lib/Lex/PPMacroExpansion.cpp | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/clang/lib/Lex/PPMacroExpansion.cpp b/clang/lib/Lex/PPMacroExpansion.cpp
index 63c48e665ae32..6f12ac80d677e 100644
--- a/clang/lib/Lex/PPMacroExpansion.cpp
+++ b/clang/lib/Lex/PPMacroExpansion.cpp
@@ -1760,7 +1760,7 @@ void Preprocessor::ExpandBuiltinMacro(Token &Tok) {
               Tok, *this, diag::err_feature_check_malformed);
           if (!II)
             return false;
-          auto BuiltinID = II->getBuiltinID();
+          unsigned BuiltinID = II->getBuiltinID();
           if (BuiltinID != 0) {
             switch (II->getBuiltinID()) {
             case Builtin::BI__builtin_cpu_is:

>From d08dcee4128582018fe786f538a11c9e16ab74b5 Mon Sep 17 00:00:00 2001
From: "Sarnie, Nick" <nick.sarnie at intel.com>
Date: Mon, 28 Jul 2025 07:49:28 -0700
Subject: [PATCH 3/3] doc + note

Signed-off-by: Sarnie, Nick <nick.sarnie at intel.com>
---
 clang/docs/LanguageExtensions.rst | 3 +++
 clang/docs/ReleaseNotes.rst       | 2 ++
 2 files changed, 5 insertions(+)

diff --git a/clang/docs/LanguageExtensions.rst b/clang/docs/LanguageExtensions.rst
index 34e1bf150aef1..29ef20f328e84 100644
--- a/clang/docs/LanguageExtensions.rst
+++ b/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``
 ---------------------------
 
diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 46290b6c39c9b..82e42ae57886c 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -98,6 +98,8 @@ Non-comprehensive list of changes in this release
   This feature is enabled by default but can be disabled by compiling with 
   ``-fno-sanitize-annotate-debug-info-traps``.
 
+- The ``__has_builtin`` function now only considers the currently active target when being used with target offloading.
+
 New Compiler Flags
 ------------------
 - New option ``-fno-sanitize-annotate-debug-info-traps`` added to disable emitting trap reasons into the debug info when compiling with trapping UBSan (e.g. ``-fsanitize-trap=undefined``).