issue-430: Introduces 8-byte alignment support for tcmalloc

git-svn-id: http://gperftools.googlecode.com/svn/trunk@175 6b5cf1ce-ec42-a296-1ba9-69fdba395a50

3 files changed, 19 insertions, 7 deletions

diff --git a/src/common.cc b/src/common.cc
index dad7372..d911e36 100644
--- a/src/common.cc
+++ b/src/common.cc
@@ -60,16 +60,16 @@ int AlignmentForSize(size_t size) {
   } else if (size >= 128) {
     // Space wasted due to alignment is at most 1/8, i.e., 12.5%.
     alignment = (1 << LgFloor(size)) / 8;
-  } else if (size >= 16) {
+  } else if (size >= kMinAlign) {
     // We need an alignment of at least 16 bytes to satisfy
     // requirements for some SSE types.
-    alignment = 16;
+    alignment = kMinAlign;
   }
   // Maximum alignment allowed is page size alignment.
   if (alignment > kPageSize) {
     alignment = kPageSize;
   }
-  CHECK_CONDITION(size < 16 || alignment >= 16);
+  CHECK_CONDITION(size < kMinAlign || alignment >= kMinAlign);
   CHECK_CONDITION((alignment & (alignment - 1)) == 0);
   return alignment;
 }
@@ -110,7 +110,7 @@ void SizeMap::Init() {
   // Compute the size classes we want to use
   int sc = 1;   // Next size class to assign
   int alignment = kAlignment;
-  CHECK_CONDITION(kAlignment <= 16);
+  CHECK_CONDITION(kAlignment <= kMinAlign);
   for (size_t size = kAlignment; size <= kMaxSize; size += alignment) {
     alignment = AlignmentForSize(size);
     CHECK_CONDITION((size % alignment) == 0);
diff --git a/src/common.h b/src/common.h
index f6d1cd6..8987255 100644
--- a/src/common.h
+++ b/src/common.h
@@ -64,12 +64,23 @@ typedef uintptr_t Length;
 #if defined(TCMALLOC_LARGE_PAGES)
 static const size_t kPageShift  = 15;
 static const size_t kNumClasses = 78;
+static const size_t kMinAlign   = 16;
 #elif defined(TCMALLOC_LARGE_PAGES64K)
 static const size_t kPageShift  = 16;
 static const size_t kNumClasses = 82;
+static const size_t kMinAlign   = 16;
+#elif defined(TCMALLOC_ALIGN_8BYTES)
+static const size_t kPageShift  = 13;
+static const size_t kNumClasses = 93;
+// Unless we force to use 8 bytes alignment we use an alignment of
+// at least 16 bytes to statisfy requirements for some SSE types.
+// Keep in mind when using the 16 bytes alignment you can have a space 
+// waste due alignment of 25%. (eg malloc of 24 bytes will get 32 bytes)
+static const size_t kMinAlign   = 8;
 #else
 static const size_t kPageShift  = 13;
 static const size_t kNumClasses = 86;
+static const size_t kMinAlign   = 16;
 #endif
 static const size_t kMaxThreadCacheSize = 4 << 20;
 
diff --git a/src/tests/tcmalloc_unittest.cc b/src/tests/tcmalloc_unittest.cc
index 079cad2..e9526ae 100644
--- a/src/tests/tcmalloc_unittest.cc
+++ b/src/tests/tcmalloc_unittest.cc
@@ -759,9 +759,10 @@ static void TestAlignmentForSize(int size) {
     CHECK((p % sizeof(void*)) == 0);
     CHECK((p % sizeof(double)) == 0);
 
-    // Must have 16-byte alignment for large enough objects
-    if (size >= 16) {
-      CHECK((p % 16) == 0);
+    // Must have 16-byte (or 8-byte in case of -DTCMALLOC_ALIGN_8BYTES) 
+    // alignment for large enough objects
+    if (size >= kMinAlign) {
+      CHECK((p % kMinAlign) == 0);
     }
   }
   for (int i = 0; i < kNum; i++) {