also optimize memory consumption for mm:orc

lib/system/alloc.nim

@@ -1265,6 +1265,17 @@ template instantiateForRegion(allocator: untyped) {.dirty.} =
   proc alloc0Impl(size: Natural): pointer =
     result = alloc0(allocator, size)
 
+  when defined(gcOrc) or defined(gcYrc):
+    proc nimAlignedAlloc0(size: Natural, alignment: int): pointer =
+      result = rawAlloc(allocator, size, alignment)
+      zeroMem(result, size)
+
+    proc nimAlignedAlloc(size: Natural, alignment: int): pointer =
+      result = rawAlloc(allocator, size, alignment)
+
+    proc nimAlignedDealloc(p: pointer) =
+      rawDealloc(allocator, p)
+
   proc deallocImpl(p: pointer) =
     dealloc(allocator, p)
 

lib/system/arc.nim

@@ -92,12 +92,23 @@ else:
 when not defined(nimHasQuirky):
   {.pragma: quirky.}
 
+# Forward declarations for native allocator alignment (implemented in alloc.nim).
+# rawAlloc's contract: result + sizeof(FreeCell) is alignment-aligned.
+# For ORC/YRC, sizeof(FreeCell) == sizeof(RefHeader).
+when (defined(gcOrc) or defined(gcYrc)) and not defined(useMalloc) and not defined(nimscript):
+  proc nimAlignedAlloc0(size: Natural, alignment: int): pointer {.gcsafe, raises: [].}
+  proc nimAlignedAlloc(size: Natural, alignment: int): pointer {.gcsafe, raises: [].}
+  proc nimAlignedDealloc(p: pointer) {.gcsafe, raises: [].}
+
 proc nimNewObj(size, alignment: int): pointer {.compilerRtl.} =
-  let hdrSize = align(sizeof(RefHeader), alignment)
-  let s = size +% hdrSize
   when defined(nimscript):
     discard
+  elif (defined(gcOrc) or defined(gcYrc)) and not defined(useMalloc):
+    let s = size +% sizeof(RefHeader)
+    result = nimAlignedAlloc0(s, alignment) +! sizeof(RefHeader)
   else:
+    let hdrSize = align(sizeof(RefHeader), alignment)
+    let s = size +% hdrSize
     result = alignedAlloc0(s, alignment) +! hdrSize
   when defined(nimArcDebug) or defined(nimArcIds):
     head(result).refId = gRefId
@@ -111,12 +122,14 @@ proc nimNewObj(size, alignment: int): pointer {.compilerRtl.} =
 
 proc nimNewObjUninit(size, alignment: int): pointer {.compilerRtl.} =
   # Same as 'newNewObj' but do not initialize the memory to zero.
-  # The codegen proved for us that this is not necessary.
-  let hdrSize = align(sizeof(RefHeader), alignment)
-  let s = size + hdrSize
   when defined(nimscript):
     discard
+  elif (defined(gcOrc) or defined(gcYrc)) and not defined(useMalloc):
+    let s = size + sizeof(RefHeader)
+    result = cast[ptr RefHeader](nimAlignedAlloc(s, alignment) +! sizeof(RefHeader))
   else:
+    let hdrSize = align(sizeof(RefHeader), alignment)
+    let s = size + hdrSize
     result = cast[ptr RefHeader](alignedAlloc(s, alignment) +! hdrSize)
   head(result).rc = 0
   when defined(gcOrc) or defined(gcYrc):
@@ -189,8 +202,11 @@ proc nimRawDispose(p: pointer, alignment: int) {.compilerRtl.} =
       if freedCells.data == nil: init(freedCells)
       freedCells.incl head(p)
     else:
-      let hdrSize = align(sizeof(RefHeader), alignment)
-      alignedDealloc(p -! hdrSize, alignment)
+      when (defined(gcOrc) or defined(gcYrc)) and not defined(useMalloc):
+        nimAlignedDealloc(p -! sizeof(RefHeader))
+      else:
+        let hdrSize = align(sizeof(RefHeader), alignment)
+        alignedDealloc(p -! hdrSize, alignment)
 
 template `=dispose`*[T](x: owned(ref T)) = nimRawDispose(cast[pointer](x), T.alignOf)
 #proc dispose*(x: pointer) = nimRawDispose(x)

tests/align/talign_heap.nim

@@ -0,0 +1,23 @@
+discard """
+  matrix: "--mm:refc; --mm:orc; --mm:arc"
+  targets: "c cpp"
+  output: "ok"
+"""
+
+# Test that heap-allocated objects with .align use small chunks,
+# not a big chunk per object (regression test for #25577).
+type U = object
+  d {.align: 32.}: int8
+
+var e: seq[ref U]
+for _ in 0 ..< 10000: e.add(new U)
+
+# Without small-chunk alignment, each object gets its own page (~46 MB).
+# With the fix, 10000 objects fit in ~1-3 MB depending on the GC.
+doAssert getTotalMem() < 8 * 1024 * 1024, "align:32 heap objects use too much memory"
+
+# Verify alignment is actually correct
+for i in 0 ..< e.len:
+  doAssert (cast[int](addr e[i].d) and 31) == 0, "field not 32-byte aligned"
+
+echo "ok"