[flang] Fix excess allocation

[klausler]

A recent patch introduced an error in an aligned byte size calculation that causes an extra word to be allocated when the original byte size is already aligned (including the case of zero). Fix.

[llvmbot]

@llvm/pr-subscribers-flang-runtime

Author: Peter Klausler (klausler)

Changes

A recent patch introduced an error in an aligned byte size calculation that causes an extra word to be allocated when the original byte size is already aligned (including the case of zero). Fix.

---

Full diff: https://github.com/llvm/llvm-project/pull/96663.diff

1 Files Affected:

• (modified) flang/runtime/pointer.cpp (+2-2)

diff --git a/flang/runtime/pointer.cpp b/flang/runtime/pointer.cpp
index aeed879f1a2e2..2979181ddd61b 100644
--- a/flang/runtime/pointer.cpp
+++ b/flang/runtime/pointer.cpp
@@ -127,7 +127,7 @@ void RTDEF(PointerAssociateRemapping)(Descriptor &pointer,
 RT_API_ATTRS void *AllocateValidatedPointerPayload(std::size_t byteSize) {
   // Add space for a footer to validate during deallocation.
   constexpr std::size_t align{sizeof(std::uintptr_t)};
-  byteSize = ((byteSize / align) + 1) * align;
+  byteSize = ((byteSize + align - 1) / align) * align;
   std::size_t total{byteSize + sizeof(std::uintptr_t)};
   void *p{std::malloc(total)};
   if (p) {
@@ -197,7 +197,7 @@ static RT_API_ATTRS std::size_t GetByteSize(
 bool RT_API_ATTRS ValidatePointerPayload(const ISO::CFI_cdesc_t &desc) {
   std::size_t byteSize{GetByteSize(desc)};
   constexpr std::size_t align{sizeof(std::uintptr_t)};
-  byteSize = ((byteSize / align) + 1) * align;
+  byteSize = ((byteSize + align - 1) / align) * align;
   const void *p{desc.base_addr};
   const std::uintptr_t *footer{reinterpret_cast<const std::uintptr_t *>(
       static_cast<const char *>(p) + byteSize)};

[vzakhari]

Thanks!