[clang] Remove #undef alloca workaround

[aeubanks]

Added in 26670dc to workaround #4885.

Windows CI and a local Windows build are happy with this change, so it seems like this has been properly fixed at some point. If this does break somebody, this can be easily reverted. (Also, Linux does the same #define alloca in system headers, so I'm not sure why it'd be different on Windows)

This is tech debt that caused breakages, see comments on #71709.

[aeubanks]

seeing if Windows CI catches anything

[llvmbot]

@llvm/pr-subscribers-clang

Author: Arthur Eubanks (aeubanks)

Changes

Added in 26670dc.

---

Full diff: https://github.com/llvm/llvm-project/pull/81534.diff

1 Files Affected:

• (modified) clang/include/clang/Basic/Builtins.h (-4)

diff --git a/clang/include/clang/Basic/Builtins.h b/clang/include/clang/Basic/Builtins.h
index f955d21169556a..6700d1903a0088 100644
--- a/clang/include/clang/Basic/Builtins.h
+++ b/clang/include/clang/Basic/Builtins.h
@@ -20,10 +20,6 @@
 #include "llvm/ADT/StringRef.h"
 #include <cstring>
 
-// VC++ defines 'alloca' as an object-like macro, which interferes with our
-// builtins.
-#undef alloca
-
 namespace clang {
 class TargetInfo;
 class IdentifierTable;

[nico]

LG, great investigation!

[Endilll]

Thank you for your time to fix that -fPIE failure caused by my PR!

[Prabhuk]

Hi, this change seems to break building (Fuchsia) Clang toolchain on Windows.

Log: https://logs.chromium.org/logs/fuchsia/buildbucket/cr-buildbucket/8756186536543250705/+/u/clang/install/stdout
Builder: https://ci.chromium.org/ui/p/fuchsia/builders/toolchain.ci/clang-windows-x64/b8756186536543250705/overview

FAILED: tools/clang/tools/extra/clang-include-fixer/tool/CMakeFiles/clang-include-fixer.dir/ClangIncludeFixer.cpp.obj 
C:\b\s\w\ir\x\w\cipd\bin\clang-cl.exe  /nologo -TP -DCLANG_REPOSITORY_STRING=\"https://llvm.googlesource.com/llvm-project\" -DGTEST_HAS_RTTI=0 -DUNICODE -D_CRT_NONSTDC_NO_DEPRECATE -D_CRT_NONSTDC_NO_WARNINGS -D_CRT_SECURE_NO_DEPRECATE -D_CRT_SECURE_NO_WARNINGS -D_GLIBCXX_ASSERTIONS -D_HAS_EXCEPTIONS=0 -D_SCL_SECURE_NO_DEPRECATE -D_SCL_SECURE_NO_WARNINGS -D_UNICODE -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS -IC:\b\s\w\ir\x\w\llvm_build\tools\clang\tools\extra\clang-include-fixer\tool -IC:\b\s\w\ir\x\w\llvm-llvm-project\clang-tools-extra\clang-include-fixer\tool -IC:\b\s\w\ir\x\w\llvm-llvm-project\clang\include -IC:\b\s\w\ir\x\w\llvm_build\tools\clang\include -IC:\b\s\w\ir\x\w\recipe_cleanup\tensorflow-venv\store\python_venv-q9i5kpsp0iun0ktmqgab125ti8\contents\Lib\site-packages\tensorflow\include -IC:\b\s\w\ir\x\w\llvm_build\include -IC:\b\s\w\ir\x\w\llvm-llvm-project\llvm\include -IC:\b\s\w\ir\x\w\llvm-llvm-project\clang-tools-extra\clang-include-fixer\tool\.. -imsvcC:\b\s\w\ir\x\w\zlib_install_target\include -imsvcC:\b\s\w\ir\x\w\zstd_install\include /DWIN32 /D_WINDOWS   /Zc:inline /Zc:__cplusplus /Oi /Brepro /bigobj /permissive- /W4  -Wextra -Wno-unused-parameter -Wwrite-strings -Wcast-qual -Wmissing-field-initializers -Wimplicit-fallthrough -Wcovered-switch-default -Wno-noexcept-type -Wnon-virtual-dtor -Wdelete-non-virtual-dtor -Wsuggest-override -Wstring-conversion -Wmisleading-indentation -Wctad-maybe-unsupported /Gw -no-canonical-prefixes /O2 /Ob2  -std:c++17 -MT  /EHs-c- /GR- -UNDEBUG /showIncludes /Fotools\clang\tools\extra\clang-include-fixer\tool\CMakeFiles\clang-include-fixer.dir\ClangIncludeFixer.cpp.obj /Fdtools\clang\tools\extra\clang-include-fixer\tool\CMakeFiles\clang-include-fixer.dir\ -c -- C:\b\s\w\ir\x\w\llvm-llvm-project\clang-tools-extra\clang-include-fixer\tool\ClangIncludeFixer.cpp
In file included from C:\b\s\w\ir\x\w\llvm-llvm-project\clang-tools-extra\clang-include-fixer\tool\ClangIncludeFixer.cpp:11:
In file included from C:\b\s\w\ir\x\w\llvm-llvm-project\clang-tools-extra\clang-include-fixer\tool\..\IncludeFixer.h:15:
In file included from C:\b\s\w\ir\x\w\llvm-llvm-project\clang\include\clang/Sema/ExternalSemaSource.h:15:
In file included from C:\b\s\w\ir\x\w\llvm-llvm-project\clang\include\clang/AST/ExternalASTSource.h:18:
In file included from C:\b\s\w\ir\x\w\llvm-llvm-project\clang\include\clang/AST/DeclBase.h:18:
In file included from C:\b\s\w\ir\x\w\llvm-llvm-project\clang\include\clang/AST/DeclarationName.h:18:
In file included from C:\b\s\w\ir\x\w\llvm-llvm-project\clang\include\clang/Basic/IdentifierTable.h:18:
In file included from C:\b\s\w\ir\x\w\llvm-llvm-project\clang\include\clang/Basic/Builtins.h:63:
C:\b\s\w\ir\x\w\llvm_build\tools\clang\include\clang/Basic/Builtins.inc(151,1): error: redefinition of enumerator 'BI_alloca'
  151 | LANGBUILTIN(_alloca, "v*z", "n", ALL_MS_LANGUAGES)
      | ^
C:\b\s\w\ir\x\w\llvm_build\tools\clang\include\clang/Basic/Builtins.inc(15,54): note: expanded from macro 'LANGBUILTIN'
   15 | #  define LANGBUILTIN(ID, TYPE, ATTRS, BUILTIN_LANG) BUILTIN(ID, TYPE, ATTRS)
      |                                                      ^
C:\b\s\w\ir\x\w\llvm-llvm-project\clang\include\clang/Basic/Builtins.h(62,34): note: expanded from macro 'BUILTIN'
   62 | #define BUILTIN(ID, TYPE, ATTRS) BI##ID,
      |                                  ^
<scratch space>(72,1): note: expanded from here
   72 | BI_alloca
      | ^
C:\b\s\w\ir\x\w\llvm_build\tools\clang\include\clang/Basic/Builtins.inc(150,1): note: previous definition is here
  150 | LIBBUILTIN(alloca, "v*z", "fn", STDLIB_H, ALL_GNU_LANGUAGES)
      | ^
C:\b\s\w\ir\x\w\llvm_build\tools\clang\include\clang/Basic/Builtins.inc(11,61): note: expanded from macro 'LIBBUILTIN'
   11 | #  define LIBBUILTIN(ID, TYPE, ATTRS, HEADER, BUILTIN_LANG) BUILTIN(ID, TYPE, ATTRS)
      |                                                             ^
C:\b\s\w\ir\x\w\llvm-llvm-project\clang\include\clang/Basic/Builtins.h(62,34): note: expanded from macro 'BUILTIN'
   62 | #define BUILTIN(ID, TYPE, ATTRS) BI##ID,
      |                                  ^
<scratch space>(71,1): note: expanded from here
   71 | BI_alloca
      | ^