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Re: possible gcse failure: not able to eliminate redundant loads

From: Dale Johannesen <dalej at apple dot com>
To: "Sanjiv Kumar Gupta, Noida" <sanjivg at noida dot hcltech dot com>
Cc: Dale Johannesen <dalej at apple dot com>, gcc at gcc dot gnu dot org
Date: Wed, 11 Dec 2002 14:24:48 -0800
Subject: Re: possible gcse failure: not able to eliminate redundant loads

On Wednesday, December 11, 2002, at 03:24 AM, Sanjiv Kumar Gupta, Noida wrote:

void func (double *a, double *b, int i)
{
       b[2] = a[1];

       for (i ; i < 3; i = i + 8)
       {
               a[4] = a[1];

       }
}

for -O2 -fno-argument-alias, I am getting multiple loads for a[1].

Oooops! I realized it just now. Basically GCC is assuming that
a[4] and a[1] may alias, hence reloading a[1] in each loop iteration.
sorry for the inconvenience caused.

But surely it should be smart enough to know they don't alias?
This is still a bug, possibly an important one for performance.

Follow-Ups:
- Re: possible gcse failure: not able to eliminate redundant loads
  - From: Daniel Berlin

References:
- RE: possible gcse failure: not able to eliminate redundant loads
  - From: Sanjiv Kumar Gupta, Noida

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