Add extension 'gnu_asm_goto_with_outputs'

[void]

Summary

Clang now supports GNU's asm goto with outputs.

[void]

Use GNU asm predicate for the "asm goto with outputs" extension.

[nickdesaulniers]

Great idea; thanks for the patch! Needs documentation. :)

clang/test/Parser/asm-goto-with-outputs.c

7 ↗

(On Diff #240657)

probably don't need a bunch of test cases, just the check for the preprocessor define? In that case, why don't you just add the above to an existing asm goto test?

[void]

Move extension test to exsiting test.

[void]

In D73319#1842900, @nickdesaulniers wrote:

Great idea; thanks for the patch! Needs documentation. :)

I can't find a place for documentation of extensions, at least not the names of extensions like gnu_asm.

clang/test/Parser/asm-goto-with-outputs.c

7 ↗

(On Diff #240657)

Sure. done.

[void]

Add description of "gnu_asm_goto_with_outputs" to the language extensions doc.

[nickdesaulniers]

In D73319#1842951, @void wrote:

In D73319#1842900, @nickdesaulniers wrote:

Great idea; thanks for the patch! Needs documentation. :)

I can't find a place for documentation of extensions, at least not the names of extensions like gnu_asm.

How about https://clang.llvm.org/docs/LanguageExtensions.html#checks-for-standard-language-features ? Then we can add both gnu_asm and gnu_asm_goto_with_outputs.

clang/test/Parser/asm-goto.c

9

ah, sorry, maybe a test that makes use of asm goto + output constraints? Maybe if you base your patch on top of the others in the series that implement the feature?

[MaskRay]

clang/docs/LanguageExtensions.rst

1273

Is the canonical spelling %l2?

[void]

In D73319#1843129, @nickdesaulniers wrote:

In D73319#1842951, @void wrote:

In D73319#1842900, @nickdesaulniers wrote:

Great idea; thanks for the patch! Needs documentation. :)

I can't find a place for documentation of extensions, at least not the names of extensions like gnu_asm.

How about https://clang.llvm.org/docs/LanguageExtensions.html#checks-for-standard-language-features ? Then we can add both gnu_asm and gnu_asm_goto_with_outputs.

That looks like it's features specific to various versions of C/C++. There were other examples like https://clang.llvm.org/docs/LanguageExtensions.html#blocks.

clang/test/Parser/asm-goto.c

9

There's one below in zoo. The order of these patches is a bit wonky because the front-end patch, which has more tests for AGWO, should go in before this one.

[void]

clang/docs/LanguageExtensions.rst

1273

Nice catch! I patched it in D69876.

[void]

I'm going to merge this into D69876 as it's closely related.

clang/docs/LanguageExtensions.rst

 ======
 
 The syntax and high level language feature description is in
 :doc:`BlockLanguageSpec<BlockLanguageSpec>`. Implementation and ABI details for
 the clang implementation are in :doc:`Block-ABI-Apple<Block-ABI-Apple>`.
 
 Query for this feature with ``__has_extension(blocks)``.
 
+ASM Goto with Output Constraints
+================================
+
+In addition to the functionality provided by `GCC's extended
+assembly`<https://gcc.gnu.org/onlinedocs/gcc/Extended-Asm.html>`_, clang
+supports output constraints with the `goto` form.
+
+The goto form of GCC's extended assembly allows the programmer to branch to a C
+label from within an inline assembly block. Clang extends this behavior by
+allowing the programmer to use output constriants:
+
+.. code-block:: c++
+
+  int foo(int x) {
+      int y;
+      asm goto("# %0 %1 %2" : "=r"(y) : "r"(x) : : err);
+      return y;
+    err:
+      return -1;
+  }
+
+It's important to note that outputs are valid only on the "fallthrough" branch.
+Using outputs on an indirect branch may result in undefined behavior. For
+example, in the function above, use of the value assigned to `y` in the `err`
+block is undefined behavior.
+
+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_binary_literals, true)
 EXTENSION(cxx_init_captures, LangOpts.CPlusPlus11)
 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(gnu_asm, LangOpts.GNUAsm)
+EXTENSION(gnu_asm_goto_with_outputs, LangOpts.GNUAsm)
 
 #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
 
 
 int a, b, c, d, e, f, g, h, i, j, k, l;
 
 void
 fgoto1 (void)
 {
   __asm__ volatile goto (""