Hi Hal,
I could not get the better result from the new “cfl-aa” as well. But
"cfl-aa" seems to be less accurate than "basicaa" for the
following basic example! Am I missing something?
Example:
int func () {
int A[100], B[100];
int i = 0, sum1 =0;
for (; i < 100; ++i) {
A[i] = B[i] = i;
}
for (i = 0; i < 100; ++i) {
sum1 += A[i] + B[i];
}
return sum1;
}
Output of “opt -mem2reg -basicaa –print-alias-sets”:
Alias Set Tracker: 2 alias sets for 4 pointer values.
AliasSet[0x3b01890, 2] may alias, Mod/Ref Pointers: (i32* %A.arrayidx, 4),
(i32* %A.arrayidx9, 4)
AliasSet[0x3b012a0, 2] may alias, Mod/Ref Pointers: (i32* %B.arrayidx2, 4),
(i32* %B.arrayidx7, 4)
Output of “opt -mem2reg –cfl-aa –print-alias-sets” and “opt –mem2reg –basicaa
–cfl-aa –print-alias-sets”:
Alias Set Tracker: 1 alias sets for 4 pointer values.
AliasSet[0x3046890, 4] may alias, Mod/Ref Pointers: (i32* %A.arrayidx, 4),
(i32* %B.arrayidx2, 4), (i32* %B.arrayidx7, 4), (i32* %A.arrayidx9, 4)
Thanks,
Vinay
-----Original Message-----
From: Hal Finkel [mailto:hfinkel at anl.gov]
Sent: Monday, September 29, 2014 6:22 PM
To: Madhusudan, Vinay
Cc: LLVM Developers Mailing List (llvmdev at cs.uiuc.edu)
Subject: Re: [LLVMdev] Alias Analysis across functions
Hi Vinay,
The new -cfl-aa has an IPA that might catch this. Also, I'm working on a new
pass to do top-down function parameter attribute propagation, which should catch
this (http://reviews.llvm.org/D4609), but it is not quite ready yet.
-Hal
----- Original Message -----
> From: "Vinay Madhusudan" <Vinay.Madhusudan at
amd.com<mailto:Vinay.Madhusudan at amd.com>>
> To: "LLVM Developers Mailing List (llvmdev at
cs.uiuc.edu<mailto:llvmdev at cs.uiuc.edu>)"
> <llvmdev at cs.uiuc.edu<mailto:llvmdev at cs.uiuc.edu>>
> Sent: Monday, September 29, 2014 12:55:18 AM
> Subject: [LLVMdev] Alias Analysis across functions
>
>
>
> Hi,
>
> I am trying to get the alias info for the following code. The alias
> analysis returns “MayAlias” for arrays “A” and “B” in both the
> functions instead of “NoAlias”. What passes should I run in opt before
> the alias analysis pass to get the accurate result?
>
> Example:
>
> //Note: static and called by func() only.
> static int sum(int *A, int *B) {
>
> int i = 0, sum1 = 0;
>
> for (i = 0; i < 100; ++i) {
> sum1 += A[i] + B[i];
> }
> return sum1;
> }
>
> int func () {
> int A[100], B[100];
> int i = 0;
> for (; i < 100; ++i) {
> A[i] = B[i] = i;
> }
> return sum(A,B);
> }
>
> Arguments to opt : “ -mem2reg -basicaa - scev-aa -print-alias-sets ”
>
> Output:
> Function: func
> Alias Set Tracker: 2 alias sets for 2 pointer values.
> AliasSet[0x2bc88b0, 2] may alias, Mod/Ref Pointers: (i32* %A.arrayidx,
> 4), (i32* %B.arrayidx2, 4)
> 1 Unknown instructions: i32 %call
> AliasSet[0x2bc8490, 1] must alias, Mod forwarding to 0x2bc88b0
>
> Function: sum
> Alias Set Tracker: 1 alias sets for 2 pointer values.
> AliasSet[0x2bcbb50, 2] may alias, Ref Pointers: (i32* %A.arrayidx, 4),
> (i32* %B.arrayidx2, 4)
>
>
> Thanks,
> Vinay
>
> _______________________________________________
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http://llvm.cs.uiuc.edu
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>
--
Hal Finkel
Assistant Computational Scientist
Leadership Computing Facility
Argonne National Laboratory
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