* calls.c (store_one_arg): Expand comment.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@45502 138bc75d-0d04-0410-961f-82ee72b054a4

1 files changed, 8 insertions, 2 deletions

diff --git a/gcc/calls.c b/gcc/calls.c
index dc915ad1ff1..f21160fa61e 100644
--- a/gcc/calls.c
+++ b/gcc/calls.c
@@ -4565,8 +4565,14 @@ store_one_arg (arg, argblock, flags, variable_size, reg_parm_stack_space)
 	    }
 	}
 
-      /*  If parm is passed both in stack and in register and offset is 
-	  greater than reg_parm_stack_space, split the offset.  */
+      /* Special handling is required if part of the parameter lies in the
+	 register parameter area.  The argument may be copied into the stack
+	 slot using memcpy(), but the original contents of the register
+	 parameter area will be restored after the memcpy() call.
+
+	 To ensure that the part that lies in the register parameter area
+	 is copied correctly, we emit a separate push for that part.  This
+	 push should be small enough to avoid a call to memcpy().  */
 #ifndef STACK_PARMS_IN_REG_PARM_AREA
       if (arg->reg && arg->pass_on_stack)
 #else