Improve zero-size allocation with safe_malloc, etc.

Summary:
The current implementations of the memory allocation functions mistake a nullptr returned from std::malloc, std::calloc, or std::realloc as a failure. The behaviour for each of std::malloc, std::calloc, and std::realloc when the size is 0 is implementation defined (ISO/IEC 9899:2018 7.22.3), and may return a nullptr.

This patch checks if space requested is zero when a nullptr is returned, retry requesting non-zero if it is.

Authored By: andusy

Reviewers: hubert.reinterpretcast, xingxue, jasonliu

Reviewed By: hubert.reinterpretcast, xingxue, abrachet

Subscribers: abrachet, jsji, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D63668

llvm-svn: 364322

1 files changed, 21 insertions, 3 deletions

diff --git a/llvm/include/llvm/Support/MemAlloc.h b/llvm/include/llvm/Support/MemAlloc.h
index ed076ffa52d..0e5869141fd 100644
--- a/llvm/include/llvm/Support/MemAlloc.h
+++ b/llvm/include/llvm/Support/MemAlloc.h
@@ -24,23 +24,41 @@ namespace llvm {
 
 LLVM_ATTRIBUTE_RETURNS_NONNULL inline void *safe_malloc(size_t Sz) {
   void *Result = std::malloc(Sz);
-  if (Result == nullptr)
+  if (Result == nullptr) {
+    // It is implementation-defined whether allocation occurs if the space
+    // requested is zero (ISO/IEC 9899:2018 7.22.3). Retry, requesting
+    // non-zero, if the space requested was zero.
+    if (Sz == 0)
+      return safe_malloc(1);
     report_bad_alloc_error("Allocation failed");
+  }
   return Result;
 }
 
 LLVM_ATTRIBUTE_RETURNS_NONNULL inline void *safe_calloc(size_t Count,
                                                         size_t Sz) {
   void *Result = std::calloc(Count, Sz);
-  if (Result == nullptr)
+  if (Result == nullptr) {
+    // It is implementation-defined whether allocation occurs if the space
+    // requested is zero (ISO/IEC 9899:2018 7.22.3). Retry, requesting
+    // non-zero, if the space requested was zero.
+    if (Count == 0 || Sz == 0)
+      return safe_malloc(1);
     report_bad_alloc_error("Allocation failed");
+  }
   return Result;
 }
 
 LLVM_ATTRIBUTE_RETURNS_NONNULL inline void *safe_realloc(void *Ptr, size_t Sz) {
   void *Result = std::realloc(Ptr, Sz);
-  if (Result == nullptr)
+  if (Result == nullptr) {
+    // It is implementation-defined whether allocation occurs if the space
+    // requested is zero (ISO/IEC 9899:2018 7.22.3). Retry, requesting
+    // non-zero, if the space requested was zero.
+    if (Sz == 0)
+      return safe_malloc(1);
     report_bad_alloc_error("Allocation failed");
+  }
   return Result;
 }