Hi all,
I am implementing a pass which needs aliasanalysis in llvm.
My pass firstly records all store or load instructions as follows:
loc[cnt++] = AA.getLocation(si/li);
Then, get each pairwise alias result.
AliasAnalysis::AliasResult ar = AA.alias(loc[i], loc[j]);
switch(ar){ case 0,1,2,3;}
And the command is: opt -load mypass.so -mypass -basicaa test.bc
The store/load in test.bc:
(1): store i64* %thd, i64** %t, align 8 //int64 *t = &thd;
(2): %1 = load i64** %t, align 8 //load t
(3): store i64* %1, i64** %t2, align 8 //int64 *t2 = t;
(4): %2 = load i64** %t, align 8 //load t
(5): %3 = load i64** %t2, align 8 //load t2
It seems that all these 5 instructions should be aliased to each other.
But the result should that only (1,2) (1,4) (2,4) (3,5) are must alias.
Others are no alias.
Who can explain these results? Any hits would be appreciated. Thank you.
----- Original Message -----> From: "Haopeng Liu" <hyliuhp at gmail.com> > To: llvmdev at cs.uiuc.edu > Sent: Monday, February 16, 2015 12:12:18 PM > Subject: [LLVMdev] alias result > > Hi all, > > I am implementing a pass which needs aliasanalysis in llvm. > > My pass firstly records all store or load instructions as follows: > loc[cnt++] = AA.getLocation(si/li); > > Then, get each pairwise alias result. > AliasAnalysis::AliasResult ar = AA.alias(loc[i], loc[j]); > switch(ar){ case 0,1,2,3;} > > And the command is: opt -load mypass.so -mypass -basicaa test.bc > > The store/load in test.bc: > > (1): store i64* %thd, i64** %t, align 8 //int64 *t = &thd; > (2): %1 = load i64** %t, align 8 //load t > (3): store i64* %1, i64** %t2, align 8 //int64 *t2 = t; > (4): %2 = load i64** %t, align 8 //load t > (5): %3 = load i64** %t2, align 8 //load t2 > > It seems that all these 5 instructions should be aliased to each > other. > > But the result should that only (1,2) (1,4) (2,4) (3,5) are must > alias. > Others are no alias.Where do %t and %t2 come from? -Hal> > Who can explain these results? Any hits would be appreciated. Thank > you. > > > > > > > _______________________________________________ > LLVM Developers mailing list > LLVMdev at cs.uiuc.edu http://llvm.cs.uiuc.edu > http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev >-- Hal Finkel Assistant Computational Scientist Leadership Computing Facility Argonne National Laboratory
t and t2 are two pointers defined in .c file. The definitions in .bc are: %thd = alloc i64, align 8 %t = alloca i64*, align 8 %t2 = alloca i64*, align 8 .c file likes this: int thd; int *t = &thd; int *t2 = t; On 2/16/15 12:28 PM, Hal Finkel wrote:> ----- Original Message ----- >> From: "Haopeng Liu" <hyliuhp at gmail.com> >> To: llvmdev at cs.uiuc.edu >> Sent: Monday, February 16, 2015 12:12:18 PM >> Subject: [LLVMdev] alias result >> >> Hi all, >> >> I am implementing a pass which needs aliasanalysis in llvm. >> >> My pass firstly records all store or load instructions as follows: >> loc[cnt++] = AA.getLocation(si/li); >> >> Then, get each pairwise alias result. >> AliasAnalysis::AliasResult ar = AA.alias(loc[i], loc[j]); >> switch(ar){ case 0,1,2,3;} >> >> And the command is: opt -load mypass.so -mypass -basicaa test.bc >> >> The store/load in test.bc: >> >> (1): store i64* %thd, i64** %t, align 8 //int64 *t = &thd; >> (2): %1 = load i64** %t, align 8 //load t >> (3): store i64* %1, i64** %t2, align 8 //int64 *t2 = t; >> (4): %2 = load i64** %t, align 8 //load t >> (5): %3 = load i64** %t2, align 8 //load t2 >> >> It seems that all these 5 instructions should be aliased to each >> other. >> >> But the result should that only (1,2) (1,4) (2,4) (3,5) are must >> alias. >> Others are no alias. > Where do %t and %t2 come from? > > -Hal > >> Who can explain these results? Any hits would be appreciated. Thank >> you. >> >> >> >> >> >> >> _______________________________________________ >> LLVM Developers mailing list >> LLVMdev at cs.uiuc.edu http://llvm.cs.uiuc.edu >> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev >>