Introduced realloc0 and reallocShared0, these procs are now used by

strs_v2 and seqs_v2. This also allowed the -d:useMalloc allocator to
drop the extra header with allocation length.

lib/system/alloc.nim

@@ -948,13 +948,18 @@ proc dealloc(allocator: var MemRegion, p: pointer) =
 
 proc realloc(allocator: var MemRegion, p: pointer, newsize: Natural): pointer =
   if newsize > 0:
-    result = alloc0(allocator, newsize)
+    result = alloc(allocator, newsize)
     if p != nil:
       copyMem(result, p, min(ptrSize(p), newsize))
       dealloc(allocator, p)
   elif p != nil:
     dealloc(allocator, p)
 
+proc realloc0(allocator: var MemRegion, p: pointer, oldsize, newsize: Natural): pointer =
+  result = realloc(allocator, p, newsize)
+  if newsize > oldsize:
+    zeroMem(cast[pointer](cast[int](result) + oldsize), newsize - oldsize)
+
 proc deallocOsPages(a: var MemRegion) =
   # we free every 'ordinarily' allocated page by iterating over the page bits:
   var it = addr(a.heapLinks)
@@ -1009,6 +1014,11 @@ template instantiateForRegion(allocator: untyped) {.dirty.} =
   proc realloc(p: pointer, newSize: Natural): pointer =
     result = realloc(allocator, p, newSize)
 
+  proc realloc0(p: pointer, oldSize, newSize: Natural): pointer =
+    result = realloc(allocator, p, newSize)
+    if newSize > oldSize:
+      zeroMem(cast[pointer](cast[int](result) + oldSize), newSize - oldSize)
+
   when false:
     proc countFreeMem(): int =
       # only used for assertions
@@ -1062,6 +1072,14 @@ template instantiateForRegion(allocator: untyped) {.dirty.} =
     else:
       result = realloc(p, newSize)
 
+  proc reallocShared0(p: pointer, oldSize, newSize: Natural): pointer =
+    when hasThreadSupport:
+      acquireSys(heapLock)
+      result = realloc0(sharedHeap, p, oldSize, newSize)
+      releaseSys(heapLock)
+    else:
+      result = realloc0(p, oldSize, newSize)
+
   when hasThreadSupport:
     template sharedMemStatsShared(v: int) =
       acquireSys(heapLock)

lib/system/ansi_c.nim

@@ -140,6 +140,8 @@ proc c_sprintf*(buf, frmt: cstring): cint {.
 
 proc c_malloc*(size: csize_t): pointer {.
   importc: "malloc", header: "<stdlib.h>".}
+proc c_calloc*(nmemb, size: csize_t): pointer {.
+  importc: "calloc", header: "<stdlib.h>".}
 proc c_free*(p: pointer) {.
   importc: "free", header: "<stdlib.h>".}
 proc c_realloc*(p: pointer, newsize: csize_t): pointer {.

lib/system/memalloc.nim

@@ -97,6 +97,22 @@ when hasAlloc:
     ## The allocated memory belongs to its allocating thread!
     ## Use `reallocShared <#reallocShared,pointer,Natural>`_ to reallocate
     ## from a shared heap.
+  proc realloc0*(p: pointer, oldSize, newSize: Natural): pointer {.noconv, rtl, tags: [],
+                                                         benign, raises: [].}
+    ## Grows or shrinks a given memory block.
+    ##
+    ## If `p` is **nil** then a new memory block is returned.
+    ## In either way the block has at least ``newSize`` bytes.
+    ## If ``newSize == 0`` and `p` is not **nil** ``realloc`` calls ``dealloc(p)``.
+    ## In other cases the block has to be freed with
+    ## `dealloc(block) <#dealloc,pointer>`_.
+    ##
+    ## The block is initialized with all bytes containing zero, so it is
+    ## somewhat safer then realloc
+    ##
+    ## The allocated memory belongs to its allocating thread!
+    ## Use `reallocShared <#reallocShared,pointer,Natural>`_ to reallocate
+    ## from a shared heap.
   proc resize*[T](p: ptr T, newSize: Natural): ptr T {.inline, benign, raises: [].} =
     ## Grows or shrinks a given memory block.
     ##
@@ -185,6 +201,19 @@ when hasAlloc:
     ## ``deallocShared(p)``.
     ## In other cases the block has to be freed with
     ## `deallocShared <#deallocShared,pointer>`_.
+  proc reallocShared0*(p: pointer, oldSize, newSize: Natural): pointer {.noconv, rtl, tags: [],
+                                                               benign, raises: [].}
+    ## Grows or shrinks a given memory block on the heap.
+    ##
+    ## When growing, the new bytes of the block is initialized with all bytes
+    ## containing zero, so it is somewhat safer then reallocShared
+    ##
+    ## If `p` is **nil** then a new memory block is returned.
+    ## In either way the block has at least ``newSize`` bytes.
+    ## If ``newSize == 0`` and `p` is not **nil** ``reallocShared`` calls
+    ## ``deallocShared(p)``.
+    ## In other cases the block has to be freed with
+    ## `deallocShared <#deallocShared,pointer>`_.
   proc resizeShared*[T](p: ptr T, newSize: Natural): ptr T {.inline, raises: [].} =
     ## Grows or shrinks a given memory block on the heap.
     ##
@@ -239,11 +268,13 @@ when defined(js):
   proc alloc(size: Natural): pointer = discard
   proc alloc0(size: Natural): pointer = discard
   proc realloc(p: pointer, newsize: Natural): pointer = discard
+  proc realloc0(p: pointer, oldsize, newsize: Natural): pointer = discard
 
   proc allocShared(size: Natural): pointer = discard
   proc allocShared0(size: Natural): pointer = discard
   proc deallocShared(p: pointer) = discard
   proc reallocShared(p: pointer, newsize: Natural): pointer = discard
+  proc reallocShared0(p: pointer, oldsize, newsize: Natural): pointer = discard
 
 
 when hasAlloc and hasThreadSupport:

lib/system/mmdisp.nim

@@ -115,17 +115,18 @@ when defined(boehmgc):
     proc realloc(p: pointer, newSize: Natural): pointer =
       result = boehmRealloc(p, newSize)
       if result == nil: raiseOutOfMem()
-    proc dealloc(p: pointer) = boehmDealloc(p)
-
-    proc allocShared(size: Natural): pointer =
-      result = boehmAlloc(size)
-      if result == nil: raiseOutOfMem()
-    proc allocShared0(size: Natural): pointer =
-      result = allocShared(size)
-    proc reallocShared(p: pointer, newSize: Natural): pointer =
+    proc realloc0(p: pointer, oldSize, newSize: Natural): pointer =
       result = boehmRealloc(p, newSize)
       if result == nil: raiseOutOfMem()
-    proc deallocShared(p: pointer) = boehmDealloc(p)
+      if newsize > oldsize:
+        zeroMem(cast[pointer](cast[int](result) + oldsize), newsize - oldsize)
+    proc dealloc(p: pointer) = boehmDealloc(p)
+
+    proc allocShared(size: Natural): pointer = alloc(size)
+    proc allocShared0(size: Natural): pointer = alloc(size)
+    proc reallocShared(p: pointer, newSize: Natural): pointer = realloc(p, newSize)
+    proc reallocShared0(p: pointer, oldSize, newSize: Natural): pointer = realloc0(p, newSize, oldSize)
+    proc deallocShared(p: pointer) = dealloc(p)
 
     when hasThreadSupport:
       proc getFreeSharedMem(): int =
@@ -274,6 +275,9 @@ elif defined(gogc):
   proc realloc(p: pointer, newsize: Natural): pointer =
     doAssert false, "not implemented"
 
+  proc realloc0(p: pointer, oldsize, newsize: Natural): pointer =
+    doAssert false, "not implemented"
+
   proc dealloc(p: pointer) =
     discard
 
@@ -286,6 +290,9 @@ elif defined(gogc):
   proc reallocShared(p: pointer, newsize: Natural): pointer =
     result = realloc(p, newsize)
 
+  proc reallocShared0(p: pointer, oldsize, newsize: Natural): pointer =
+    result = realloc0(p, oldsize, newsize)
+
   proc deallocShared(p: pointer) = dealloc(p)
 
   when hasThreadSupport:
@@ -356,39 +363,21 @@ elif defined(gogc):
 
 elif (defined(nogc) or defined(gcDestructors)) and defined(useMalloc):
 
-  # libc realloc() does not zero out memory, so this is handled here. Every
-  # allocated buffer is prepended with the size of the allocation which is used
-  # to deduce which part of the buffer to zero.
-
   when not defined(useNimRtl):
 
-    proc alloc(size: Natural): pointer =
-      var x = c_malloc (size + sizeof(size)).csize_t
-      if x == nil: raiseOutOfMem()
-      cast[ptr int](x)[] = size
-      result = cast[pointer](cast[int](x) + sizeof(size))
-
-    proc alloc0(size: Natural): pointer =
-      result = alloc(size)
-      zeroMem(result, size)
-
-    proc realloc(p: pointer, newsize: Natural): pointer =
-      var x = cast[pointer](cast[int](p) - sizeof(newsize))
-      let oldsize = cast[ptr int](x)[]
-      x = c_realloc(x, (newsize + sizeof(newsize)).csize_t)
-      if x == nil: raiseOutOfMem()
-      cast[ptr int](x)[] = newsize
-      result = cast[pointer](cast[int](x) + sizeof(newsize))
+    proc alloc(size: Natural): pointer = c_malloc(size.csize_t)
+    proc alloc0(size: Natural): pointer = c_calloc(size.csize_t, 1)
+    proc realloc(p: pointer, newsize: Natural): pointer = c_realloc(p, newSize.csize_t)
+    proc realloc0(p: pointer, oldsize, newsize: Natural): pointer =
+      result = realloc(p, newsize.csize_t)
       if newsize > oldsize:
         zeroMem(cast[pointer](cast[int](result) + oldsize), newsize - oldsize)
+    proc dealloc(p: pointer) = c_free(p)
 
-    proc dealloc(p: pointer) = c_free(cast[pointer](cast[int](p) - sizeof(int)))
-
-    # Shared allocators map to the regular ones
-
-    proc allocShared(size: Natural): pointer = alloc(size.csize_t)
+    proc allocShared(size: Natural): pointer = alloc(size)
     proc allocShared0(size: Natural): pointer = alloc0(size)
-    proc reallocShared(p: pointer, newsize: Natural): pointer = realloc(p, newsize.csize_t)
+    proc reallocShared(p: pointer, newsize: Natural): pointer = realloc(p, newsize)
+    proc reallocShared0(p: pointer, oldsize, newsize: Natural): pointer = realloc0(p, oldsize, newsize)
     proc deallocShared(p: pointer) = dealloc(p)
 
     proc GC_disable() = discard

lib/system/seqs_v2.nim

@@ -69,7 +69,9 @@ proc prepareSeqAdd(len: int; p: pointer; addlen, elemSize: int): pointer {.
         q.cap = cap
         result = q
       else:
-        var q = cast[ptr NimSeqPayloadBase](reallocShared(p, headerSize + elemSize * cap))
+        let oldSize = headerSize + elemSize * p.cap
+        let newSize = headerSize + elemSize * cap
+        var q = cast[ptr NimSeqPayloadBase](reallocShared0(p, oldSize, newSize))
         q.allocated = 1
         q.cap = cap
         result = q

lib/system/strs_v2.nim

@@ -51,7 +51,7 @@ proc prepareAdd(s: var NimStringV2; addlen: int) {.compilerRtl.} =
         copyMem(unsafeAddr s.p.data[0], unsafeAddr oldP.data[0], s.len)
   elif s.len + addlen > s.p.cap:
     let cap = max(s.len + addlen, resize(s.p.cap))
-    s.p = cast[ptr NimStrPayload](reallocShared(s.p, contentSize(cap)))
+    s.p = cast[ptr NimStrPayload](reallocShared0(s.p, contentSize(s.p.cap), contentSize(cap)))
     s.p.cap = cap
 
 proc nimAddCharV1(s: var NimStringV2; c: char) {.compilerRtl.} =