From: "Igor Shevlyakov" <igor@microunity.com>
To: <gcc@gcc.gnu.org>, <gcc-help@gcc.gnu.org>
Subject: Advice needed how to avoid generation of extra sign_extends in .md file
Date: Thu, 03 Oct 2002 18:07:00 -0000 [thread overview]
Message-ID: <002001c26b42$ac2589b0$1e0756c0@medusa> (raw)
Hi everybody,
I wonder if somebody know how to make back-end generate better code
under following conditions:
- 32 bit opearations always sign extend their result into whole 64-bit
result registers.
- conditional branches work only on 64-bit registers
- loads are always sign-extending.
now if we have
int64 a, b;
int32 c, d, f;
c = d + f;
a = b + c;
How to avoid sign_extend before second plus since result of 'addsi3' was
already extended?
Even worse:
int16 *pi, j;
int64 a,b;
j = *pi + 3;
a = b + j;
Doesn't really requires any extensions since *pi already sign extended
target register and we could use same instruction to add 16-bits as for
add 32-bits and result will be 64-bit sign extended in that case.
But I couldn't come up with idea how to teach .md file all that.
Thanks a lot
Igor
next reply other threads:[~2002-10-04 1:07 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2002-10-03 18:07 Igor Shevlyakov [this message]
2002-10-03 19:14 ` Richard Henderson
2002-10-04 9:51 ` Jim Wilson
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