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Re: Bug in optimize_bitfield_assignment_op()?

From: Ian Lance Taylor <iant at google dot com>
To: "Bingfeng Mei" <bmei at broadcom dot com>
Cc: "gcc\ at gcc dot gnu dot org" <gcc at gcc dot gnu dot org>
Date: Fri, 19 Dec 2008 07:33:28 -0800
Subject: Re: Bug in optimize_bitfield_assignment_op()?
References: <7FB04A5C213E9943A72EE127DB74F0AD24F97C27DC@SJEXCHCCR02.corp.ad.broadcom.com>

"Bingfeng Mei" <bmei@broadcom.com> writes:

> Here the bitpos = 0, bitsize = 52.  HOST_WIDE_INT for our processor
> is 32, though 64-bit long long type is supported.  The marked
> statement produces a mask of 0xfffff, thus causes the upper 32-bit
> removed later.  Is this a potential bug, or did I miss something?

gcc requires that the size of HOST_WIDE_INT be at least as large as
BITS_PER_WORD.  In your case BITS_PER_WORD is presumably 64; if it is
not, then the condition at the start of
optimize_bitfield_assignment_op should have returned false
immediately.

See need_64bit_hwint in config.gcc.

Ian

References:
- Bug in optimize_bitfield_assignment_op()?
  - From: Bingfeng Mei

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