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*From*: Ziemowit Laski <zlaski at apple dot com>*To*: Richard Henderson <rth at redhat dot com>*Cc*: Geoff Keating <geoffk at geoffk dot org>, Fariborz Jahanian <fjahanian at apple dot com>, GCC Patches <gcc-patches at gcc dot gnu dot org>*Date*: Thu, 7 Oct 2004 14:33:39 -0700*Subject*: Re: Patch gcc-4.0 should not apply mathematical associative rules for addition or multiplication*References*: <2B2F21A1-16FF-11D9-957B-000A95BA54A6@apple.com> <m28yalosbv.fsf@greed.local> <m3sm8sorfl.fsf@merlin.cs.tamu.edu> <B829D438-1710-11D9-BB5A-000A95B1F520@geoffk.org> <C6712220-1712-11D9-A3AB-000A95D7CD40@apple.com> <028CC984-1718-11D9-BB5A-000A95B1F520@geoffk.org> <D02AF864-17BA-11D9-957B-000A95BA54A6@apple.com> <8D0B228A-17F4-11D9-957B-000A95BA54A6@apple.com> <20041007203854.GA10557@redhat.com> <92D8D46E-18A1-11D9-8693-000D9330C50E@apple.com> <20041007211711.GC10671@redhat.com>

On 7 Oct 2004, at 14.17, Richard Henderson wrote:

On Thu, Oct 07, 2004 at 01:43:41PM -0700, Ziemowit Laski wrote:You should allow

X op C1 op C2 to combine to X op C3

if C1 op C2 is exactly representable. Which happens very often.

Yes, but don't 'X op C1' and 'X op C3' also need to be exactly representable?

Not so far as I can determine. What specifically leads you to believe this?

Actually, I overshot a bit. :-( You need to know that 'X op C1' and 'C1 op C2' are exactly representable. Otherwise, you may have

Actually, Dale just popped his head in and suggested that the folding might be OK if C1 == C2. :-)

**Follow-Ups**:

**References**:**Patch gcc-4.0 should not apply mathematical associative rules for addition or multiplication***From:*Fariborz Jahanian

**Re: Patch gcc-4.0 should not apply mathematical associative rules for addition or multiplication***From:*Geoffrey Keating

**Re: Patch gcc-4.0 should not apply mathematical associative rules for addition or multiplication***From:*Gabriel Dos Reis

**Re: Patch gcc-4.0 should not apply mathematical associative rules for addition or multiplication***From:*Geoff Keating

**Re: Patch gcc-4.0 should not apply mathematical associative rules for addition or multiplication***From:*Dale Johannesen

**Re: Patch gcc-4.0 should not apply mathematical associative rules for addition or multiplication***From:*Geoff Keating

**Re: Patch gcc-4.0 should not apply mathematical associative rules for addition or multiplication***From:*Fariborz Jahanian

**Re: Patch gcc-4.0 should not apply mathematical associative rules for addition or multiplication***From:*Fariborz Jahanian

**Re: Patch gcc-4.0 should not apply mathematical associative rules for addition or multiplication***From:*Richard Henderson

**Re: Patch gcc-4.0 should not apply mathematical associative rules for addition or multiplication***From:*Ziemowit Laski

**Re: Patch gcc-4.0 should not apply mathematical associative rules for addition or multiplication***From:*Richard Henderson

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