[LLVMdev] Is it possible to create a variable that aliases a field in a struct ?

[sebastien deldon (PGI)]

Hi all,

Given assert code in alias detection I've opted for a simplification in expressing field address :

target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v16:16:16-v32:32:32-v64:64:64-v128:128:128-n16:32:64"


%struct._dpowk_16 = type < { [32 x [32 x double]], [32 x [32 x double]], [32 x [32 x i64]] } >

@_dpowk_16 = common global %struct._dpowk_16  zeroinitializer, align 16
@r_d_field = alias [32 x [32 x double]] * getelementptr (%struct._dpowk_16 * @_dpowk_16, i32 0, i32 1)

Now I've got following error from opt :

opt -O2 -S gblmod2.ll -o gblmod2.opt.ll
opt: /home/sdeldon/tools/llvm/3.2/llvm-3.2.src/include/llvm/Support/Casting.h:208: typename llvm::cast_retty<To, From>::ret_type llvm::cast(const Y&) [with X = llvm::GlobalValue, Y = llvm::Value*]: Assertion `isa<X>(Val) && "cast<Ty>() argument of incompatible type!"' failed.
0  opt             0x00000000010e3abf
1  opt             0x00000000010e5a22
2  libpthread.so.0 0x0000003dd0a0f710
3  libc.so.6       0x0000003dd0232925 gsignal + 53
4  libc.so.6       0x0000003dd0234105 abort + 373
5  libc.so.6       0x0000003dd022ba4e
6  libc.so.6       0x0000003dd022bb10 __assert_perror_fail + 0
7  opt             0x0000000000bf238f
8  opt             0x0000000001083af1 llvm::MPPassManager::runOnModule(llvm::Module&) + 497
9  opt             0x0000000001083c6b llvm::PassManagerImpl::run(llvm::Module&) + 171
10 opt             0x000000000053b307 main + 6999
11 libc.so.6       0x0000003dd021ed1d __libc_start_main + 253
12 opt             0x000000000052c5c9
Stack dump:
0.            Program arguments: opt -O2 -S gblmod2.ll -o gblmod2.opt.ll
1.            Running pass 'Global Variable Optimizer' on module 'gblmod2.ll'.

Is it a BUG ?

Seb


From: sebastien deldon (PGI)
Sent: Friday, June 13, 2014 11:05 AM
To: llvmdev
Subject: Is it possible to create a variable that aliases a field in a struct ?

Hi all,

I would like to create a variable that aliases a field in a struct like :

%struct._dpowk_16 = type < { [32 x [32 x double]], [32 x [32 x double]], [32 x [32 x i64]] } >

@_dpowk_16 = common addrspace(1) global %struct._dpowk_16  zeroinitializer, align 16
@r_d_alias = alias [32 x [32 x double]] addrspace(1) * bitcast (i8 addrspace(1) * getelementptr (i8 addrspace(1) * bitcast (%struct._dpowk_16 addrspace(1)* @_dpowk_16 to i8 addrspace(1) *), i64 8192) to [32 x [32 x double]] addrspace(1) * )

When I use opt I got following message :

Aliasee should be either GlobalValue or bitcast of GlobalValue
[32 x [32 x double]] addrspace(1)* @r_d_alias
Broken module found, compilation aborted!
0  opt             0x00000000010e3abf
1  opt             0x00000000010e5a22
2  libpthread.so.0 0x0000003dd0a0f710
3  libc.so.6       0x0000003dd0232925 gsignal + 53
4  libc.so.6       0x0000003dd0234105 abort + 373
5  opt             0x00000000010a3e8a
6  opt             0x000000000107c654 llvm::FPPassManager::doFinalization(llvm::Module&) + 84
7  opt             0x000000000107df79 llvm::FunctionPassManagerImpl::doFinalization(llvm::Module&) + 105
8  opt             0x000000000053b25d main + 6829
9  libc.so.6       0x0000003dd021ed1d __libc_start_main + 253
10 opt             0x000000000052c5c9
Stack dump:

0.                Program arguments: opt -O2 -S gblmod.ll -o gblmod.opt.ll

Is there a way to have a global value that reflects a field in a struct ?

Thanks for your answers
Seb

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