commit 3153915714c48a57fecb5e41ca10b7fb16df52f6
author Andreas Gampe <agampe@google.com> Wed Apr 25 13:34:29 2018 -0700
committer Andreas Gampe <agampe@google.com> Fri Apr 27 09:04:29 2018 -0700
tree 9d259c272733c89475da3d202027d58d35015c55
parent a111ab1f5703ce839983a86caffae9bcad34c86f

ART: Use alloca to avoid an expensive allocation

Attempt to avoid a new[] for common cases.

Bug: 78568168
Test: m test-art-host
Change-Id: I393ecdeef58f885f6e7a6ffa216ed37a4726c227

libdexfile/dex/dex_file_verifier.cc

diff --git a/libdexfile/dex/dex_file_verifier.cc b/libdexfile/dex/dex_file_verifier.cc
index 3f72a25..a91567f 100644
--- a/libdexfile/dex/dex_file_verifier.cc
+++ b/libdexfile/dex/dex_file_verifier.cc
@@ -1300,7 +1300,19 @@
     return false;
   }
 
-  std::unique_ptr<uint32_t[]> handler_offsets(new uint32_t[handlers_size]);
+  // Avoid an expensive allocation, if possible.
+  std::unique_ptr<uint32_t[]> handler_offsets_uptr;
+  uint32_t* handler_offsets;
+  constexpr size_t kAllocaMaxSize = 1024;
+  if (handlers_size < kAllocaMaxSize/sizeof(uint32_t)) {
+    handler_offsets =
+        AlignDown(reinterpret_cast<uint32_t*>(alloca((handlers_size + 1) * sizeof(uint32_t))),
+                  alignof(uint32_t[]));
+  } else {
+    handler_offsets_uptr.reset(new uint32_t[handlers_size]);
+    handler_offsets = handler_offsets_uptr.get();
+  }
+
   if (!CheckAndGetHandlerOffsets(code_item, &handler_offsets[0], handlers_size)) {
     return false;
   }