Re: C vs. FORTRAN aliasing

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Article #2205

#2205

From: Anton Rang
Date: Wed, 21 Nov 1990 17:59

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In article <15704.274a7509@levels.sait.edu.au> ccml@levels.sait.edu.au writes:
>I wrote:
>> 	SUBROUTINE BLAH(X,Y)
>> 	INTEGER X,Y
>> 	X = 3
>> 	Y = 2
>> 	IF (A(X) .EQ. 0) ...
>> 
>> [edited down]
>>   A compiler for FORTRAN can optimize the test to be A(3) since it
>> knows that the assignment to Y can never change X.  A compiler for C,
>> in the absence of interprocedural aliasing information, cannot do the
>> same.
>
>Assuming that there was no 'EQUIVALENCE (a,b)'  in the routine
>which does the 'CALL BLAH(a,b)'!

  If there was, then the program is erroneous (not legal FORTRAN, I'm
not sure if 'erroneous' is the term ANSI uses in the FORTRAN spec).
In a legal FORTRAN program, X and Y can never be aliased (strictly
speaking, program execution can not depend on whether X and Y are
aliased or not).

	Anton
   
+---------------------------+------------------+-------------+
| Anton Rang (grad student) | rang@cs.wisc.edu | UW--Madison |
+---------------------------+------------------+-------------+

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From: rang@cs.wisc.edu (Anton Rang)
Newsgroups: comp.lang.misc
Subject: Re: C vs. FORTRAN aliasing
Message-ID: <RANG.90Nov21115939@nexus.cs.wisc.edu>
Date: 21 Nov 90 17:59:39 GMT
References: <RANG.90Nov18160113@nexus.cs.wisc.edu>
 <15704.274a7509@levels.sait.edu.au>
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In-Reply-To: ccml@levels.sait.edu.au's message of 21 Nov 90 12:37:29 GMT

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