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Re: [PATCH] Fix alpha and arm bootstrap failures
- From: Richard Henderson <rth at redhat dot com>
- To: Roger Sayle <roger at www dot eyesopen dot com>
- Cc: Richard Earnshaw <rearnsha at arm dot com>, Brad Lucier <lucier at math dot purdue dot edu>, gcc-patches at gcc dot gnu dot org, Kazu Hirata <kazu at cs dot umass dot edu>
- Date: Wed, 26 Feb 2003 14:59:59 -0800
- Subject: Re: [PATCH] Fix alpha and arm bootstrap failures
- References: <20030226215530.GA23068@redhat.com> <Pine.LNX.4.44.0302261433340.21288-100000@www.eyesopen.com>
On Wed, Feb 26, 2003 at 02:50:37PM -0700, Roger Sayle wrote:
> But we handle const, pure, nothrow and malloc attributes on
> arbitrary non-libcall functions just fine without having to use
> REG_EQUAL notes.
How's that? What other mechanism do we use to prove that
two calls to foo are identical?
> I agree we could add special cases to ignore REG_EQUAL notes
> whereever we also have a REG_RETVAL note, but I was under the
> impression that we're trying to move away from libcalls.
No, we're trying to move away from emit_libcall{,value}.
That's not the same thing.
> We can also recover much of our ability to CSE/GCSE by using
> perfectly valid REG_EQUAL notes, such as "REG_EQUAL (lt:DF (reg:DF 1)
> (reg: DF 2))" rather than the current "REG_EQUAL (expr_list ((symbol_ref
> "__ltfdf2") (expr_list (reg:DF 1)..."
Except that lt:DF would evaluate to FLOAT_STORE_FLAG_VALUE and lt:SI
would evaluate to STORE_FLAG_VALUE. Neither of which is what __ltfdf2
returns. And this is completely irrelevant for a user's
extern int foo(int) __attribute__((const));
> Do you have a strong preference on the best mid/long term solution?
Long term, tree-ssa will make this all moot. There's no point
in trying to change our scheme for rtl.
r~