[libc] Enable remaining string functions on the GPU

[jhuber6]

Summary:
We previously had to disable these string functions because they were
not compatible with the definitions coming from the GNU / host
environment. The GPU, when exporting its declarations, has a very
difficult requirement that it be compatible with the host environment as
both sides of the compilation need to agree on definitions and what's
present.

This patch more or less gives up an just copies the definitions as
expected by glibc if they are provided that way, otherwise we fall
back to the accepted way. This is the alternative solution to an
existing PR which instead disable's GCC's handling.

[llvmbot]

@llvm/pr-subscribers-backend-x86
@llvm/pr-subscribers-clang

@llvm/pr-subscribers-libc

Changes

Summary:
We previously had to disable these string functions because they were
not compatible with the definitions coming from the GNU / host
environment. The GPU, when exporting its declarations, has a very
difficult requirement that it be compatible with the host environment as
both sides of the compilation need to agree on definitions and what's
present.

This patch more or less gives up an just copies the definitions as
expected by glibc if they are provided that way, otherwise we fall
back to the accepted way. This is the alternative solution to an
existing PR which instead disable's GCC's handling.

---

Full diff: https://github.com/llvm/llvm-project/pull/68346.diff

3 Files Affected:

• (modified) clang/lib/Headers/llvm_libc_wrappers/string.h (+70-3)
• (modified) libc/config/gpu/entrypoints.txt (+16)
• (modified) libc/docs/gpu/support.rst (+19-8)

diff --git a/clang/lib/Headers/llvm_libc_wrappers/string.h b/clang/lib/Headers/llvm_libc_wrappers/string.h
index 027c415c1d0f8f3..49c8234d7bed492 100644
--- a/clang/lib/Headers/llvm_libc_wrappers/string.h
+++ b/clang/lib/Headers/llvm_libc_wrappers/string.h
@@ -13,9 +13,6 @@
 #error "This file is for GPU offloading compilation only"
 #endif
 
-// FIXME: The GNU headers provide C++ standard compliant headers when in C++
-// mode and the LLVM libc does not. We cannot enable memchr, strchr, strchrnul,
-// strpbrk, strrchr, strstr, or strcasestr until this is addressed.
 #include_next <string.h>
 
 #if __has_include(<llvm-libc-decls/string.h>)
@@ -26,8 +23,78 @@
 
 #pragma omp begin declare target
 
+// The GNU headers provide C++ standard compliant headers when in C++ mode and
+// the LLVM libc does not. We need to manually provide the definitions using the
+// same prototypes.
+#if defined(__cplusplus) && defined(__GLIBC__) &&                              \
+    defined(__CORRECT_ISO_CPP_STRING_H_PROTO)
+
+#ifndef __LIBC_ATTRS
+#define __LIBC_ATTRS
+#endif
+
+extern "C" {
+void *memccpy(void *__restrict, const void *__restrict, int,
+              size_t) __LIBC_ATTRS;
+extern "C++" void *memchr(void *__s, int __c, size_t __n) noexcept __LIBC_ATTRS;
+extern "C++" const void *memchr(const void *__s, int __c,
+                                size_t __n) noexcept __LIBC_ATTRS;
+int memcmp(const void *, const void *, size_t) __LIBC_ATTRS;
+void *memcpy(void *__restrict, const void *__restrict, size_t) __LIBC_ATTRS;
+void *memmem(const void *, size_t, const void *, size_t) __LIBC_ATTRS;
+void *memmove(void *, const void *, size_t) __LIBC_ATTRS;
+void *mempcpy(void *__restrict, const void *__restrict, size_t) __LIBC_ATTRS;
+extern "C++" void *memrchr(void *__s, int __c,
+                           size_t __n) noexcept __LIBC_ATTRS;
+extern "C++" const void *memrchr(const void *__s, int __c,
+                                 size_t __n) noexcept __LIBC_ATTRS;
+void *memset(void *, int, size_t) __LIBC_ATTRS;
+char *stpcpy(char *__restrict, const char *__restrict) __LIBC_ATTRS;
+char *stpncpy(char *__restrict, const char *__restrict, size_t) __LIBC_ATTRS;
+extern "C++" char *strcasestr(char *__haystack,
+                              const char *__needle) noexcept __LIBC_ATTRS;
+extern "C++" const char *strcasestr(const char *__haystack,
+                                    const char *__needle) noexcept __LIBC_ATTRS;
+char *strcat(char *__restrict, const char *__restrict) __LIBC_ATTRS;
+extern "C++" char *strchr(char *__s, int __c) noexcept __LIBC_ATTRS;
+extern "C++" const char *strchr(const char *__s, int __c) noexcept __LIBC_ATTRS;
+extern "C++" char *strchrnul(char *__s, int __c) noexcept __LIBC_ATTRS;
+extern "C++" const char *strchrnul(const char *__s,
+                                   int __c) noexcept __LIBC_ATTRS;
+int strcmp(const char *, const char *) __LIBC_ATTRS;
+int strcoll(const char *, const char *) __LIBC_ATTRS;
+char *strcpy(char *__restrict, const char *__restrict) __LIBC_ATTRS;
+size_t strcspn(const char *, const char *) __LIBC_ATTRS;
+char *strdup(const char *) __LIBC_ATTRS;
+size_t strlen(const char *) __LIBC_ATTRS;
+char *strncat(char *, const char *, size_t) __LIBC_ATTRS;
+int strncmp(const char *, const char *, size_t) __LIBC_ATTRS;
+char *strncpy(char *__restrict, const char *__restrict, size_t) __LIBC_ATTRS;
+char *strndup(const char *, size_t) __LIBC_ATTRS;
+size_t strnlen(const char *, size_t) __LIBC_ATTRS;
+extern "C++" char *strpbrk(char *__s,
+                           const char *__accept) noexcept __LIBC_ATTRS;
+extern "C++" const char *strpbrk(const char *__s,
+                                 const char *__accept) noexcept __LIBC_ATTRS;
+extern "C++" char *strrchr(char *__s, int __c) noexcept __LIBC_ATTRS;
+extern "C++" const char *strrchr(const char *__s,
+                                 int __c) noexcept __LIBC_ATTRS;
+size_t strspn(const char *, const char *) __LIBC_ATTRS;
+extern "C++" char *strstr(char *__haystack,
+                          const char *__needle) noexcept __LIBC_ATTRS;
+extern "C++" const char *strstr(const char *__haystack,
+                                const char *__needle) noexcept __LIBC_ATTRS;
+char *strtok(char *__restrict, const char *__restrict) __LIBC_ATTRS;
+char *strtok_r(char *__restrict, const char *__restrict,
+               char **__restrict) __LIBC_ATTRS;
+size_t strxfrm(char *__restrict, const char *__restrict, size_t) __LIBC_ATTRS;
+}
+
+#else
 #include <llvm-libc-decls/string.h>
 
+#endif
+
 #pragma omp end declare target
 
 #undef __LIBC_ATTRS
diff --git a/libc/config/gpu/entrypoints.txt b/libc/config/gpu/entrypoints.txt
index ad68216a76b9429..dcaca15b500cbe9 100644
--- a/libc/config/gpu/entrypoints.txt
+++ b/libc/config/gpu/entrypoints.txt
@@ -22,21 +22,31 @@ set(TARGET_LIBC_ENTRYPOINTS
 
     # string.h entrypoints
     libc.src.string.bcmp
+    libc.src.string.bcopy
     libc.src.string.bzero
+    libc.src.string.index
     libc.src.string.memccpy
+    libc.src.string.memchr
     libc.src.string.memcmp
     libc.src.string.memcpy
     libc.src.string.memmem
     libc.src.string.memmove
     libc.src.string.mempcpy
+    libc.src.string.memrchr
     libc.src.string.memset
+    libc.src.string.rindex
     libc.src.string.stpcpy
     libc.src.string.stpncpy
     libc.src.string.strcasecmp
+    libc.src.string.strcasestr
     libc.src.string.strcat
+    libc.src.string.strchr
+    libc.src.string.strchrnul
     libc.src.string.strcmp
+    libc.src.string.strcoll
     libc.src.string.strcpy
     libc.src.string.strcspn
+    libc.src.string.strdup
     libc.src.string.strlcat
     libc.src.string.strlcpy
     libc.src.string.strlen
@@ -44,10 +54,16 @@ set(TARGET_LIBC_ENTRYPOINTS
     libc.src.string.strncat
     libc.src.string.strncmp
     libc.src.string.strncpy
+    libc.src.string.strndup
     libc.src.string.strnlen
+    libc.src.string.strpbrk
+    libc.src.string.strrchr
+    libc.src.string.strsep
     libc.src.string.strspn
+    libc.src.string.strstr
     libc.src.string.strtok
     libc.src.string.strtok_r
+    libc.src.string.strxfrm
 
     # stdlib.h entrypoints
     libc.src.stdlib.abs
diff --git a/libc/docs/gpu/support.rst b/libc/docs/gpu/support.rst
index fd27273ed562e49..beca7b587a05215 100644
--- a/libc/docs/gpu/support.rst
+++ b/libc/docs/gpu/support.rst
@@ -45,37 +45,48 @@ string.h
 Function Name  Available  RPC Required
 =============  =========  ============
 bcmp           |check|
+bcopy          |check|
 bzero          |check|
+index          |check|
 memccpy        |check|
-memchr         
+memchr         |check|
 memcmp         |check|
 memcpy         |check|
+memmem         |check|
 memmove        |check|
 mempcpy        |check|
-memrchr
+memrchr        |check|
 memset         |check|
+rindex         |check|
 stpcpy         |check|
 stpncpy        |check|
+strcasecmp     |check|
+strcasestr     |check|
 strcat         |check|
-strchr         
+strchr         |check|
+strchrnul      |check|
 strcmp         |check|
+strcoll        |check|
 strcpy         |check|
 strcspn        |check|
+strdup         |check|
 strlcat        |check|
 strlcpy        |check|
 strlen         |check|
+strncasecmp    |check|
 strncat        |check|
 strncmp        |check|
 strncpy        |check|
+strndup        |check|
 strnlen        |check|
-strpbrk        
-strrchr        
+strpbrk        |check|
+strrchr        |check|
+strsep         |check|
 strspn         |check|
-strstr         
+strstr         |check|
 strtok         |check|
 strtok_r       |check|
-strdup
-strndup
+strxfrm        |check|
 =============  =========  ============
 
 stdlib.h

[jdoerfert]

Seems a reasonable solution, given that nothing in this space is really nice and clean.

Nobody complained for a while, LG.