Fix PR3724 by searching for the largest free block when

allocating memory in the JIT.  This is insanely inefficient, but
hey, most people implement their own memory managers anyway.

Patch by Eric Yew!

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@66472 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/ExecutionEngine/JIT/JITMemoryManager.cpp b/lib/ExecutionEngine/JIT/JITMemoryManager.cpp
index 0dcc71f837c6c526e16c85f498b069fc635550f0..b2bf8529d45667b6ffbed5a513b6f55ecc4ffd01 100644 (file)
--- a/lib/ExecutionEngine/JIT/JITMemoryManager.cpp
+++ b/lib/ExecutionEngine/JIT/JITMemoryManager.cpp
@@ -278,10 +278,27 @@ namespace {
     /// startFunctionBody - When a function starts, allocate a block of free
     /// executable memory, returning a pointer to it and its actual size.
     unsigned char *startFunctionBody(const Function *F, uintptr_t &ActualSize) {
-      CurBlock = FreeMemoryList;
       
+      FreeRangeHeader* candidateBlock = FreeMemoryList;
+      FreeRangeHeader* head = FreeMemoryList;
+      FreeRangeHeader* iter = head->Next;
+
+      uintptr_t largest = candidateBlock->BlockSize;
+      
+      // Search for the largest free block
+      while (iter != head) {
+          if (iter->BlockSize > largest) {
+              largest = iter->BlockSize;
+              candidateBlock = iter;
+          }
+          iter = iter->Next;
+      }
+      
+      // Select this candidate block for allocation
+      CurBlock = candidateBlock;
+
       // Allocate the entire memory block.
-      FreeMemoryList = FreeMemoryList->AllocateBlock();
+      FreeMemoryList = candidateBlock->AllocateBlock();
       ActualSize = CurBlock->BlockSize-sizeof(MemoryRangeHeader);
       return (unsigned char *)(CurBlock+1);
     }