work around GCC name mangling bug

It seems that older versions of GCC (4.0 and older, at least) generate
assembly files with duplicate symbols for function templates which
differ only by the attributes of the templated types.  Newer versions
have no such problem, but we need to support both, hence the
workaround in this commit of using a dedicated, non-template "alias"
function where we previously used "cast<alias_t>".

Author: dicej

src/common.h

@@ -59,7 +59,15 @@ typedef uint64_t uintptr_t;
 #    error "unsupported architecture"
 #  endif
 
-typedef intptr_t alias_t;
+namespace vm {
+
+inline intptr_t&
+alias(void* p, unsigned offset)
+{
+  return *reinterpret_cast<intptr_t*>(static_cast<uint8_t*>(p) + offset);
+}
+
+} // namespace vm
 
 #else // not _MSC_VER
 
@@ -88,7 +96,16 @@ typedef intptr_t alias_t;
 #    error "unsupported architecture"
 #  endif
 
-typedef intptr_t __attribute__((__may_alias__)) alias_t;
+namespace vm {
+
+typedef intptr_t __attribute__((__may_alias__)) intptr_alias_t;
+inline intptr_alias_t&
+alias(void* p, unsigned offset)
+{
+  return *reinterpret_cast<intptr_alias_t*>(static_cast<uint8_t*>(p) + offset);
+}
+
+} // namespace vm
 
 #endif // not _MSC_VER
 

src/machine.cpp

@@ -2145,8 +2145,8 @@ class HeapClient: public Heap::Client {
     memcpy(dst, src, n * BytesPerWord);
 
     if (hashTaken(t, src)) {
-      cast<alias_t>(dst, 0) &= PointerMask;
-      cast<alias_t>(dst, 0) |= ExtendedMark;
+      alias(dst, 0) &= PointerMask;
+      alias(dst, 0) |= ExtendedMark;
       extendedWord(t, dst, base) = takeHash(t, src);
     }
   }
@@ -2781,7 +2781,7 @@ allocate3(Thread* t, Allocator* allocator, Machine::AllocationType type,
 
     memset(o, 0, sizeInBytes);
 
-    cast<alias_t>(o, 0) = FixedMark;
+    alias(o, 0) = FixedMark;
 
     t->m->fixedFootprint += total;
 
@@ -2796,7 +2796,7 @@ allocate3(Thread* t, Allocator* allocator, Machine::AllocationType type,
 
     memset(o, 0, sizeInBytes);
 
-    cast<alias_t>(o, 0) = FixedMark;
+    alias(o, 0) = FixedMark;
 
     return o;
   }

src/machine.h

@@ -1878,8 +1878,9 @@ setObjectClass(Thread*, object o, object value)
 {
   cast<object>(o, 0)
     = reinterpret_cast<object>
-    (reinterpret_cast<alias_t>(value)
-     | (reinterpret_cast<alias_t>(cast<object>(o, 0)) & (~PointerMask)));
+    (reinterpret_cast<intptr_alias_t>(value)
+     | (reinterpret_cast<intptr_alias_t>
+        (cast<object>(o, 0)) & (~PointerMask)));
 }
 
 inline const char*
@@ -2094,19 +2095,19 @@ setType(Thread* t, Machine::Type type, object value)
 inline bool
 objectFixed(Thread*, object o)
 {
-  return (cast<alias_t>(o, 0) & (~PointerMask)) == FixedMark;
+  return (alias(o, 0) & (~PointerMask)) == FixedMark;
 }
 
 inline bool
 objectExtended(Thread*, object o)
 {
-  return (cast<alias_t>(o, 0) & (~PointerMask)) == ExtendedMark;
+  return (alias(o, 0) & (~PointerMask)) == ExtendedMark;
 }
 
 inline bool
 hashTaken(Thread*, object o)
 {
-  return (cast<alias_t>(o, 0) & (~PointerMask)) == HashTakenMark;
+  return (alias(o, 0) & (~PointerMask)) == HashTakenMark;
 }
 
 inline unsigned
@@ -2237,7 +2238,7 @@ markHashTaken(Thread* t, object o)
 
   ACQUIRE_RAW(t, t->m->heapLock);
 
-  cast<alias_t>(o, 0) |= HashTakenMark;
+  alias(o, 0) |= HashTakenMark;
   t->m->heap->pad(o);
 }
 

src/util.cpp

@@ -66,32 +66,32 @@ inline object
 getTreeNodeValue(Thread*, object n)
 {
   return reinterpret_cast<object>
-    (cast<alias_t>(n, TreeNodeValue) & PointerMask);
+    (alias(n, TreeNodeValue) & PointerMask);
 }
 
 inline void
 setTreeNodeValue(Thread* t, object n, object value)
 {
-  alias_t red = cast<alias_t>(n, TreeNodeValue) & (~PointerMask);
+  intptr_t red = alias(n, TreeNodeValue) & (~PointerMask);
 
   set(t, n, TreeNodeValue, value);
 
-  cast<alias_t>(n, TreeNodeValue) |= red;
+  alias(n, TreeNodeValue) |= red;
 }
 
 inline bool
 treeNodeRed(Thread*, object n)
 {
-  return (cast<alias_t>(n, TreeNodeValue) & (~PointerMask)) == 1;
+  return (alias(n, TreeNodeValue) & (~PointerMask)) == 1;
 }
 
 inline void
 setTreeNodeRed(Thread*, object n, bool red)
 {
   if (red) {
-    cast<alias_t>(n, TreeNodeValue) |= 1;
+    alias(n, TreeNodeValue) |= 1;
   } else {
-    cast<alias_t>(n, TreeNodeValue) &= PointerMask;
+    alias(n, TreeNodeValue) &= PointerMask;
   }
 }