Use GC.malloc_atomic with GC.realloc, not Pointer#realloc (#12391)

spec/std/io/io_spec.cr

@@ -72,7 +72,7 @@ private class SimpleIOMemory < IO
 
   private def resize_to_capacity(capacity)
     @capacity = capacity
-    @buffer = @buffer.realloc(@capacity)
+    @buffer = GC.realloc(@buffer, @capacity)
   end
 end
 

src/gc.cr

@@ -93,8 +93,11 @@ module GC
   # If *pointer* was allocated with `malloc_atomic`, the same constraints apply.
   #
   # The return value is a pointer that may be identical to *pointer* or different.
-  def self.realloc(pointer : Void*, size : Int) : Void*
-    realloc(pointer, LibC::SizeT.new(size))
+  #
+  # WARNING: Memory allocated using `Pointer.malloc` must be reallocated using
+  # `Pointer#realloc` instead.
+  def self.realloc(pointer : T*, size : Int) : T* forall T
+    realloc(pointer.as(Void*), LibC::SizeT.new(size)).as(T*)
   end
 end
 

src/io/memory.cr

@@ -460,6 +460,6 @@ class IO::Memory < IO
 
   private def resize_to_capacity(capacity)
     @capacity = capacity
-    @buffer = @buffer.realloc(@capacity)
+    @buffer = GC.realloc(@buffer, @capacity)
   end
 end

src/pointer.cr

@@ -347,6 +347,9 @@ struct Pointer(T)
   # ptr = ptr.realloc(8)
   # ptr # [1, 2, 3, 4, 0, 0, 0, 0]
   # ```
+  #
+  # WARNING: Memory allocated using `GC.malloc` or `GC.malloc_atomic` must be
+  # reallocated using `GC.realloc` instead.
   def realloc(size : Int)
     if size < 0
       raise ArgumentError.new("Negative size")

src/string.cr

@@ -256,7 +256,7 @@ class String
 
     # Try to reclaim some memory if capacity is bigger than what was requested
     if bytesize < capacity
-      str = str.realloc(bytesize.to_u32 + HEADER_SIZE + 1)
+      str = GC.realloc(str, bytesize.to_u32 + HEADER_SIZE + 1)
     end
 
     str_header = str.as({Int32, Int32, Int32}*)

src/string/builder.cr

@@ -128,6 +128,6 @@ class String::Builder < IO
 
   private def resize_to_capacity(capacity)
     @capacity = capacity
-    @buffer = @buffer.realloc(@capacity)
+    @buffer = GC.realloc(@buffer, @capacity)
   end
 end