From mboxrd@z Thu Jan  1 00:00:00 1970
From: Per Bothner <per@bothner.com>
To: Richard Kenner <kenner@vlsi1.ultra.nyu.edu>
Cc: gcc@gcc.gnu.org
Subject: Re: ICE in change_address at emit_rtl.c
Date: Sun, 25 Nov 2001 10:27:00 -0000
Message-ID: <3C0137ED.6080604@bothner.com>
References: <10111251307.AA27532@vlsi1.ultra.nyu.edu>
X-SW-Source: 2001-11/msg01202.html
Message-ID: <20011125102700.s8hW6a2JIUtzITkntWSxXh3N1xSqY8lZyU22Xr55Mv8@z>

SAVE_EXPR causes problems when generating Java bytecodes.  We do
this by using the Java parser to build a tree, but then bypassing
the  backend to emit .class files directly.  The latter does not have
a register allocation pass.  That is ok, because we cn use as many
"registers" as we need, and all local variables can be assigned to
"registers" using a trivial stack discipline.  However, SAVE_EXPRs
cause problems.  It is easy enough to assign a jvm register to a
SAVE_EXPR, but there is no way to reclaim it.  This is not a
fatal flaw, but it is wasteful, as it would bloat the stack frame
of a naive interpreter.

This is one reason why fold causes problems as it sometimes
creates SAVE_EXPR.  Using  a scoped temporary:
   let tmp := expr in BODY
would be preferable for us.

Another problem with fold is that it does not obey Java rules
for expression evaluation order.  We would probably want to add
a flag to force it to do that.

    --Per