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Re: [PATCH 01/10] rs6000: Clobber XER[CA] in all user asm statements
- From: Hans-Peter Nilsson <hp at bitrange dot com>
- To: Segher Boessenkool <segher at kernel dot crashing dot org>
- Cc: gcc-patches at gcc dot gnu dot org, dje dot gcc at gmail dot com
- Date: Mon, 19 Jan 2015 01:53:06 -0500 (EST)
- Subject: Re: [PATCH 01/10] rs6000: Clobber XER[CA] in all user asm statements
- Authentication-results: sourceware.org; auth=none
- References: <cover dot 1418024189 dot git dot segher at kernel dot crashing dot org> <7a4b7bd73211032ecf856de06a20e14a323e08ba dot 1418024189 dot git dot segher at kernel dot crashing dot org>
On Mon, 8 Dec 2014, Segher Boessenkool wrote:
> A lot of old user code clobbers the carry bit without telling the compiler
> about it. This used to just work, because the compiler never used the bit
> outside of a single RTL instruction. But that will change. Let's clobber
> the carry bit in every asm; this isn't very expensive.
There's also the option of clobbering it only if it's not
explicitly mentioned in the asm, say with a singleton
regclass, see cris_md_asm_clobbers.
brgds, H-P