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Re: Optimizer Questions
- To: Klaus Didrich <kd at cs dot tu-berlin dot de>
- Subject: Re: Optimizer Questions
- From: Jeffrey A Law <law at cygnus dot com>
- Date: Wed, 24 Jun 1998 18:07:14 -0600
- cc: egcs at cygnus dot com
- Reply-To: law at cygnus dot com
In message <13712.56819.874875.486735@polyxena>you write:
>
> [1] The flag -fmove-all-movables does not seem to have any effect:
>
> gcc -fmove-all-movables -S T.c
> gcc -S T.c
>
> produce the same assembler file (no moving in either case), as do
>
> gcc -O2 -fno-move-all-movables -S T.c
> gcc -O2 -S T.c
Probably because there are no additional moveables in your code.
In larger loops, the compiler's heuristics may indicate that a particular
movable isn't profitable to move. This flag tells the compiler to move
it anyway.
> [2] Code moving produces an empty loop, which is not removed.
> (See below for the output with -O2)
This is a "feature" and the documented behavior of the compiler. That
may change (there's a recent long thread on this topic that I need to
review).
jeff