[llvm] Simplify hot-path size computations in BumpPtrAllocator. (PR #101467)

[Nikita Popov via llvm-commits]

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@@ -149,28 +149,30 @@ class BumpPtrAllocatorImpl
     // Keep track of how many bytes we've allocated.
     BytesAllocated += Size;
 
-    size_t Adjustment = offsetToAlignedAddr(CurPtr, Alignment);
-    assert(Adjustment + Size >= Size && "Adjustment + Size must not overflow");
+    uintptr_t AlignedPtr = alignAddr(CurPtr, Alignment);
 
     size_t SizeToAllocate = Size;
 #if LLVM_ADDRESS_SANITIZER_BUILD
     // Add trailing bytes as a "red zone" under ASan.
     SizeToAllocate += RedZoneSize;
 #endif
 
+    uintptr_t AllocEndPtr = AlignedPtr + SizeToAllocate;
+    assert(AllocEndPtr >= uintptr_t(CurPtr) &&
+           "Alignment + Size must not overflow");
+
     // Check if we have enough space.
-    if (LLVM_LIKELY(Adjustment + SizeToAllocate <= size_t(End - CurPtr)
+    if (LLVM_LIKELY(AllocEndPtr <= uintptr_t(End)
                     // We can't return nullptr even for a zero-sized allocation!
                     && CurPtr != nullptr)) {
-      char *AlignedPtr = CurPtr + Adjustment;
-      CurPtr = AlignedPtr + SizeToAllocate;
+      CurPtr = reinterpret_cast<char *>(AllocEndPtr);
       // Update the allocation point of this memory block in MemorySanitizer.
       // Without this, MemorySanitizer messages for values originated from here
       // will point to the allocation of the entire slab.
-      __msan_allocated_memory(AlignedPtr, Size);
+      __msan_allocated_memory(reinterpret_cast<char *>(AlignedPtr), Size);
       // Similarly, tell ASan about this space.
       __asan_unpoison_memory_region(AlignedPtr, Size);
-      return AlignedPtr;
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nikic wrote:

This has two casts now?

https://github.com/llvm/llvm-project/pull/101467