[LLVMdev] Problem with "Does not dominate all uses"

[Cameron Zwarich]

In your original file, %6 is defined in if.end11 and is used in cond.end. if.end11 branches to cond.true and cond.false, both of which branch unconditionally to cond.end. Therefore %6 dominates its use.

In your second file %18 is defined in end.11 and used in cond.end. However, end.11 no longer dominates cond.end because you have rewritten all branches to go through the switch statement in loopEntry, and it is possible to take the path from entry to loopEntry to cond.end without going through end.11.

Cameron

On Aug 20, 2012, at 6:24 AM, Rinaldini Julien <julien.rinaldini at heig-vd.ch> wrote:

> Hi!
> 
> I'm having some trouble with a pass I'm writing.
> 
> I'm using DemotePHIToStack to remove all phi node in my code with this code (this is the first thing I do in my pass):
> 
>    // Erase phi node
>    vector<PHINode*> phis;
>    for (Function::iterator i=f->begin();i!=f->end();++i) {
>        for(BasicBlock::iterator b=i->begin();b!=i->end();++b) {
>            if(isa<PHINode>(b)) {
>                PHINode *phi= cast<PHINode>(b);
>                phis.push_back(phi);
>            }   
>        }   
>    }   
> 
>    for(vector<PHINode*>::iterator i=phis.begin();i!=phis.end();++i) {
>        PHINode *phi = *i; 
>        DemotePHIToStack(phi,NULL);
>    }
> 
> If I only run this code, I obtain this code (see safer.phi.ll).
> If I run the rest of my pass, I obtain this code (see safer.phi.obfu.ll)
> 
> And I got this error for the file safer.phi.obfu.ll:
> 
> Instruction does not dominate all uses!
>  %18 = load i8** %key.addr, align 8, !dbg !322
>  call void @Safer_Expand_Userkey(i8* %18, i8* %19, i32 %cond.reload, i32 0, i8* %arraydecay), !dbg !322
> Instruction does not dominate all uses!
>  %19 = load i8** %key.addr, align 8, !dbg !322
>  call void @Safer_Expand_Userkey(i8* %18, i8* %19, i32 %cond.reload, i32 0, i8* %arraydecay), !dbg !322
> Broken module found, compilation aborted!
> 0  opt             0x0000000000946d3f
> 1  opt             0x0000000000947229
> 2  libpthread.so.0 0x00007fcba9ff2170
> 3  libc.so.6       0x00007fcba925dfa5 gsignal + 53
> 4  libc.so.6       0x00007fcba925f428 abort + 328 
> 5  opt             0x000000000090951d
> 6  opt             0x00000000008e609f llvm::FPPassManager::runOnFunction(llvm::Function&) + 607 
> 7  opt             0x00000000008e60f3 llvm::FPPassManager::runOnModule(llvm::Module&) + 51
> 8  opt             0x00000000008e5c6c llvm::MPPassManager::runOnModule(llvm::Module&) + 524 
> 9  opt             0x00000000008e5d77 llvm::PassManagerImpl::run(llvm::Module&) + 151 
> 10 opt             0x00000000004a1d99 main + 3385
> 11 libc.so.6       0x00007fcba924a725 __libc_start_main + 245 
> 12 opt             0x00000000004a6135
> Stack dump:
> 0.  Program arguments: opt -load ../../../build/Release+Asserts/lib/LLVMobfuscation.so -flattening src/ciphers/safer/safer.bc -o src/ciphers/safer/safer.bc -stats 
> 1.  Running pass 'Function Pass Manager' on module 'src/ciphers/safer/safer.bc'.
> 2.  Running pass 'Module Verifier' on function '@safer_k64_setup'
> make: *** [src/ciphers/safer/safer.o] Aborted
> 
> 
> So the problem come from the bloc if.end11 and cond.end. I understand the dominate problem, but the thing is that these instruction (in first file):
> 
> if.end11:                                         ; preds = %if.end8
>  %6 = load i8** %key.addr, align 8, !dbg !322 
>  %7 = load i8** %key.addr, align 8, !dbg !322
>  ...
> 
> cond.end:                                         ; preds = %cond.false, %cond.true
>  %cond.reload = load i32* %cond.reg2mem
>  %10 = load %union.Symmetric_key** %skey.addr, align 8, !dbg !322
>  %safer = bitcast %union.Symmetric_key* %10 to %struct.safer_key*, !dbg !322
>  %key13 = getelementptr inbounds %struct.safer_key* %safer, i32 0, i32 0, !dbg !322
>  %arraydecay = getelementptr inbounds [217 x i8]* %key13, i32 0, i32 0, !dbg !322
>  call void @Safer_Expand_Userkey(i8* %6, i8* %7, i32 %cond.reload, i32 0, i8* %arraydecay), !dbg !322
>  store i32 0, i32* %retval, !dbg !323
>  br label %return, !dbg !323
> 
> 
> are the same in the second file:
> 
> if.end11:                                         ; preds = %loopEntry                                                                     
>  %18 = load i8** %key.addr, align 8, !dbg !322                                                                                            
>  %19 = load i8** %key.addr, align 8, !dbg !322
>  ...
> 
> cond.end:                                         ; preds = %loopEntry                                                                     
>  %cond.reload = load i32* %cond.reg2mem                                                                                                   
>  %24 = load %union.Symmetric_key** %skey.addr, align 8, !dbg !322
>  %safer = bitcast %union.Symmetric_key* %24 to %struct.safer_key*, !dbg !322                                                              
>  %key13 = getelementptr inbounds %struct.safer_key* %safer, i32 0, i32 0, !dbg !322                                                       
>  %arraydecay = getelementptr inbounds [217 x i8]* %key13, i32 0, i32 0, !dbg !322                                                         
>  call void @Safer_Expand_Userkey(i8* %18, i8* %19, i32 %cond.reload, i32 0, i8* %arraydecay), !dbg !322                                   
>  store i32 0, i32* %retval, !dbg !323
>  store i32 14, i32* %switchVar
>  br label %loopEnd
> 
> I don't understant why the first time I don't have a dominate problem, but the second time I do (I'm pretty sure it's because of the rest of my pass but I can't figure where because the code that cause problem it's the same in the both version).
> 
> Any idea?
> 
> Thx,
> Cheers<safer.phi.ll><safer.phi.obfu.ll>_______________________________________________
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