[libc] Use is aligned builtin instead of ptrtoint

[jhuber6]

Summary:
This avoids a ptrtoint by just using the clang builtin. This is clang
specific but only clang can compile GPU code anyway so I do not bother
with a fallback.

[llvmbot]

@llvm/pr-subscribers-libc

Author: Joseph Huber (jhuber6)

Changes

Summary:
This avoids a ptrtoint by just using the clang builtin. This is clang
specific but only clang can compile GPU code anyway so I do not bother
with a fallback.

---

Full diff: https://github.com/llvm/llvm-project/pull/146402.diff

1 Files Affected:

• (modified) libc/src/__support/GPU/allocator.cpp (+2-2)

diff --git a/libc/src/__support/GPU/allocator.cpp b/libc/src/__support/GPU/allocator.cpp
index b2f2953e4f285..dfa03782a442e 100644
--- a/libc/src/__support/GPU/allocator.cpp
+++ b/libc/src/__support/GPU/allocator.cpp
@@ -541,7 +541,7 @@ void deallocate(void *ptr) {
     return;
 
   // All non-slab allocations will be aligned on a 2MiB boundary.
-  if ((reinterpret_cast<uintptr_t>(ptr) & SLAB_ALIGNMENT) == 0)
+  if (__builtin_is_aligned(ptr, SLAB_ALIGNMENT + 1))
     return impl::rpc_free(ptr);
 
   // The original slab pointer is the 2MiB boundary using the given pointer.
@@ -556,7 +556,7 @@ void *reallocate(void *ptr, uint64_t size) {
     return gpu::allocate(size);
 
   // Non-slab allocations are considered foreign pointers so we fail.
-  if ((reinterpret_cast<uintptr_t>(ptr) & SLAB_ALIGNMENT) == 0)
+  if (__builtin_is_aligned(ptr, SLAB_ALIGNMENT + 1))
     return nullptr;
 
   // The original slab pointer is the 2MiB boundary using the given pointer.