[clang] add __has_extension(gnu_asm_goto_with_outputs_full)

[nickdesaulniers]

Summary

Also move the line about __has_extension(gnu_asm_goto_with_outputs) so
that it is more generally about asm goto, not the paragraph on symbolic
references.

[nickdesaulniers]

clang/docs/LanguageExtensions.rst

1596

err...clang-17

[efriedma]

LGTM

[nickdesaulniers]

• rebase

[void]

LGTM

[nickdesaulniers]

• final rebase

clang/docs/LanguageExtensions.rst

 Query for this feature with ``__has_extension(blocks)``.
 
 ASM Goto with Output Constraints
 ================================
 
 Outputs may be used along any branches from the ``asm goto`` whether the
 branches are taken or not.
 
+Query for this feature with ``__has_extension(gnu_asm_goto_with_outputs)``.
+
+Prior to clang-16, the output may only be used safely when the indirect
+branches are not taken.  Query for this difference with
+``__has_extension(gnu_asm_goto_with_outputs_full)``.
+
 When using tied-outputs (i.e. outputs that are inputs and outputs, not just
 outputs) with the `+r` constraint, there is a hidden input that's created
 before the label, so numeric references to operands must account for that.
 
 .. code-block:: c++
 
   int foo(int x) {
       // %0 and %1 both refer to x
.. code-block:: c++
 
   int foo(int x) {
       asm goto("# %[x] %l[err]" : [x]"+r"(x) : : : err);
       return x;
     err:
       return -1;
   }
 
-Query for this feature with ``__has_extension(gnu_asm_goto_with_outputs)``.
-
 Objective-C Features
 ====================
 
 Related result types
 --------------------
 
 According to Cocoa conventions, Objective-C methods with certain names
 ("``init``", "``alloc``", etc.) always return objects that are an instance of

clang/include/clang/Basic/Features.def

 EXTENSION(cxx_variable_templates, LangOpts.CPlusPlus)
 // Miscellaneous language extensions
 EXTENSION(overloadable_unmarked, true)
 EXTENSION(pragma_clang_attribute_namespaces, true)
 EXTENSION(pragma_clang_attribute_external_declaration, true)
 EXTENSION(statement_attributes_with_gnu_syntax, true)
 EXTENSION(gnu_asm, LangOpts.GNUAsm)
 EXTENSION(gnu_asm_goto_with_outputs, LangOpts.GNUAsm)
+EXTENSION(gnu_asm_goto_with_outputs_full, LangOpts.GNUAsm)
 EXTENSION(matrix_types, LangOpts.MatrixTypes)
 EXTENSION(matrix_types_scalar_division, true)
 EXTENSION(cxx_attributes_on_using_declarations, LangOpts.CPlusPlus11)
 
 FEATURE(cxx_abi_relative_vtable, LangOpts.CPlusPlus && LangOpts.RelativeCXXABIVTables)
 
 // CUDA/HIP Features
 FEATURE(cuda_noinline_keyword, LangOpts.CUDA)
 
 #undef EXTENSION
 #undef FEATURE

clang/test/Parser/asm-goto.c

 // RUN: %clang_cc1 -triple i386-pc-linux-gnu -fsyntax-only -verify %s
 // RUN: %clang_cc1 -triple x86_64-pc-linux-gnu -fsyntax-only -verify %s
 
 #if !__has_extension(gnu_asm)
 #error Extension 'gnu_asm' should be available by default
 #endif
 #if !__has_extension(gnu_asm_goto_with_outputs)
 #error Extension 'gnu_asm_goto_with_outputs' should be available by default
 #endif
+#if !__has_extension(gnu_asm_goto_with_outputs_full)
+#error Extension 'gnu_asm_goto_with_outputs_full' should be available by default
+#endif
 
 int a, b, c, d, e, f, g, h, i, j, k, l;
 
 void test(void) {
   __asm__ volatile goto (""
             :: [a] "r" (a), [b] "r" (b), [c] "r" (c), [d] "r" (d),
                [e] "r" (e), [f] "r" (f), [g] "r" (g), [h] "r" (h),
                [i] "r" (i), [j] "r" (j), [k] "r" (k), [l] "r" (l)