easy enough to ascertain, just print the addr of the items in question
Sun
On Fri, Jan 28, 2011 at 7:15 AM, Ye, Mei <mei...@amd.com> wrote:
> That’s what I think.
>
>
>
> -Mei
>
>
>
> *From:* Roy Ju [mailto:roy_dc...@yahoo.com]
> *Sent:* Thursday, January 27, 2011 3:09 PM
> *To:* open64-devel@lists.sourceforge.net; Ye, Mei
> *Subject:* Re: [Open64-devel] Fortran parameter no-alias rule?
>
>
>
> Does this mean that 416.gamess violates the Fortran param no aliasing rule?
>
>
>
> Roy
>
> --- On *Thu, 1/27/11, Ye, Mei <mei...@amd.com>* wrote:
>
>
> From: Ye, Mei <mei...@amd.com>
> Subject: [Open64-devel] Fortran parameter no-alias rule?
> To: "open64-devel@lists.sourceforge.net" <
> open64-devel@lists.sourceforge.net>
> Date: Thursday, January 27, 2011, 10:11 AM
>
> Hello,
>
>
>
> I am seeking your opinion on what is the best way to solve a problem that I
> observed.
>
>
>
> Compiler assumes that formal parameters based on different symbols in
> Fortran programs are not aliased. This leads to a runtime error for CPU2006
> 416.gamess when "-Ofast -LNO:fusion=2" is used.
>
>
>
> In the following code snippet, formal parameter array "D" and "DO" in
> subroutine “SYMTRD” have the same storage as their corresponding actual
> parameter "X(I40)". Therefore the read of "D" in the 1st loop must alias
> with the write of "DO" in the 2nd loop. When the two outermost loops are
> fused together, we got incorrect results.
>
>
>
> In summary, the Fortran parameter no-alias rule makes loop transformations
> illegal.
>
>
>
> For legality concern, we could rely on interprocedual analysis to track
> whether formal parameters have the same base. But compiler analysis tends
> to be conservative and therefore could hurt performance. It might not
> always be feasible to implement "copy-in copy-out" which may hurt
> performance as well.
>
>
>
> Will that be reasonable to treat this as an user error?
>
>
>
> Code snippet:
>
> callsite:
>
> CALL SYMTRD(X(I30),X(I40),X(I10),X(I40),X(I60),IA,L1,L1)
>
>
>
> callee:
>
> SUBROUTINE SYMTRD(SH,D,DT,DO,DOD,IA,N,NDIM)
>
> DIMENSION SH(*),D(*),DT(NDIM,*),DO(*),DOD(*),IA(*)
>
> ......
>
> DO 140 I = 1,N
>
> DO 120 J = 1,N
>
> DTEMP = ZERO
>
> DO 100 K = 1,N
>
> IK = IA(I)+K
>
> IF (I .LT. K) IK = IA(K)+I
>
> JK = IA(J)+K
>
> IF (J .LT. K) JK = IA(K)+J
>
> DTEMP = DTEMP+SH(IK)*D(JK) // read of D
>
> 100 CONTINUE
>
> DT(I,J) = DTEMP
>
> 120 CONTINUE
>
> 140 CONTINUE
>
>
>
> IJ = 0
>
> DO 200 I = 1,N
>
> DO 180 J = 1,I
>
> IJ = IJ+1
>
> DTEMP = ZERO
>
> DO 160 K = 1,N
>
> JK = IA(J)+K
>
> IF (J .LT. K) JK = IA(K)+J
>
> DTEMP = DTEMP+DT(I,K)*SH(JK)
>
> 160 CONTINUE
>
> DO(IJ) = DTEMP // write of DO
>
> 180 CONTINUE
>
> 200 CONTINUE
>
>
>
> -Mei Ye
>
>
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