[libc] Use generic/builtin.h for Emscripten in memory utils #177474
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@llvm/pr-subscribers-libc Author: None (google-yfyang) ChangesWASM supports bulk memory operations and can benefit from using generic/builtin.h. Full diff: https://github.com/llvm/llvm-project/pull/177474.diff 3 Files Affected:
diff --git a/libc/src/string/memory_utils/inline_memcpy.h b/libc/src/string/memory_utils/inline_memcpy.h
index 13975e6b3bd0e..931d2821be3a9 100644
--- a/libc/src/string/memory_utils/inline_memcpy.h
+++ b/libc/src/string/memory_utils/inline_memcpy.h
@@ -31,7 +31,7 @@
#elif defined(LIBC_TARGET_ARCH_IS_ANY_RISCV)
#include "src/string/memory_utils/riscv/inline_memcpy.h"
#define LIBC_SRC_STRING_MEMORY_UTILS_MEMCPY inline_memcpy_riscv
-#elif defined(LIBC_TARGET_ARCH_IS_GPU)
+#elif defined(LIBC_TARGET_ARCH_IS_GPU) || defined(LIBC_TARGET_ARCH_IS_WASM)
#include "src/string/memory_utils/generic/builtin.h"
#define LIBC_SRC_STRING_MEMORY_UTILS_MEMCPY inline_memcpy_builtin
#else
diff --git a/libc/src/string/memory_utils/inline_memmove.h b/libc/src/string/memory_utils/inline_memmove.h
index 71a28c32e4c56..31627669b06bf 100644
--- a/libc/src/string/memory_utils/inline_memmove.h
+++ b/libc/src/string/memory_utils/inline_memmove.h
@@ -29,7 +29,7 @@
#define LIBC_SRC_STRING_MEMORY_UTILS_MEMMOVE_SMALL_SIZE \
inline_memmove_no_small_size
#define LIBC_SRC_STRING_MEMORY_UTILS_MEMMOVE_FOLLOW_UP inline_memmove_riscv
-#elif defined(LIBC_TARGET_ARCH_IS_GPU)
+#elif defined(LIBC_TARGET_ARCH_IS_GPU) || defined(LIBC_TARGET_ARCH_IS_WASM)
#include "src/string/memory_utils/generic/builtin.h"
#define LIBC_SRC_STRING_MEMORY_UTILS_MEMMOVE_SMALL_SIZE \
inline_memmove_no_small_size
diff --git a/libc/src/string/memory_utils/inline_memset.h b/libc/src/string/memory_utils/inline_memset.h
index e41bdb626d60e..da85f09d0db57 100644
--- a/libc/src/string/memory_utils/inline_memset.h
+++ b/libc/src/string/memory_utils/inline_memset.h
@@ -27,7 +27,7 @@
#elif defined(LIBC_TARGET_ARCH_IS_ANY_RISCV)
#include "src/string/memory_utils/riscv/inline_memset.h"
#define LIBC_SRC_STRING_MEMORY_UTILS_MEMSET inline_memset_riscv
-#elif defined(LIBC_TARGET_ARCH_IS_GPU)
+#elif defined(LIBC_TARGET_ARCH_IS_GPU) || defined(LIBC_TARGET_ARCH_IS_WASM)
#include "src/string/memory_utils/generic/builtin.h"
#define LIBC_SRC_STRING_MEMORY_UTILS_MEMSET inline_memset_builtin
#else
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Diff between emscripten-core/emscripten#26151 and LLVM 21.1.8 has this too: diff --git a/libc/src/__support/macros/properties/architectures.h b/libc/src/__support/macros/properties/architectures.h
index c88956ff4114..817ced4e95c2 100644
--- a/libc/src/__support/macros/properties/architectures.h
+++ b/libc/src/__support/macros/properties/architectures.h
@@ -41,6 +41,10 @@
#define LIBC_TARGET_ARCH_IS_ARM
#endif
+#if defined(__wasm__)
+#define LIBC_TARGET_ARCH_IS_WASM
+#endif
+
#if defined(__aarch64__) || defined(__arm64__) || defined(_M_ARM64)
#define LIBC_TARGET_ARCH_IS_AARCH64
#endifShould we include this here too? |
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Author
This already went into the HEAD 4 months ago. https://github.com/llvm/llvm-project/blob/main/libc/src/__support/macros/properties/architectures.h. Presumably LLVM 21.1.8 isn't new enough to see this change reflected. |
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@michaelrj-google Could you please take a look? |
jhuber6
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Jan 23, 2026
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I'm assuming you've verified that __builtin_memmove and similar do not emit libcalls in their implementation? Should be fine.
sbc100
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Jan 23, 2026
This makes llvm libc on par with libcxx and libcxxabi. #26058 The remaining local changes to libc sources are very minor and is all in llvm/llvm-project#177474. Once both of these PRs go in, we can try syncing it to the LLVM upstream HEAD.
michaelrj-google
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Jan 23, 2026
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LGTM as long as you've confirmed that the builtins don't call the library functions (as jhuber suggested)
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Yes, https://godbolt.org/z/T69z9TYc8. Looks like no libcalls are emitted. |
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WASM supports bulk memory operations and can benefit from using generic/builtin.h.