LLVM use chains

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#1

Hi,
   I have:
   ...
@.str1 = private unnamed_addr constant [21 x i8] c"Now f is a function\0A\00", align 1
; Function Attrs: ssp uwtable
define i32 @_Z1fv() #2 {
entry:
   %call = call i32 (i8*, ...)* @printf(i8* getelementptr inbounds ([21 x i8]* @.str1, i32 0, i32 0))
   ret i32 0
}

Then I get after trying to erase the function from the module:

511 GV->eraseFromParent();
(gdb) p GV->dump()

; Function Attrs: ssp uwtable
define i32 @_Z1fv() #2 {
entry:
   %call = call i32 (i8*, ...)* @printf(i8* getelementptr inbounds ([21 x i8]* @.str1, i32 0, i32 0))
   ret i32 0
}

(gdb) n
513 }
(gdb) br llvm::AssemblyWriter::printModule(llvm::Module const*)
(gdb) p m_CurTransaction->getModule()->dump()
llvm::AssemblyWriter::printGlobal (this=0x7fff5fbfe850, GV=0x107274058) at /Users/vvassilev/workspace/root/interpreter/llvm/src/lib/IR/AsmWriter.cpp:1444
1444 if (GV->isMaterializable())
(gdb) p GV->use_empty()
$78 = false
(gdb) p GV->use_back()
$79 = (class llvm::User *) 0x107279b88
(gdb) p GV->use_back()->dump()
i8* getelementptr inbounds ([21 x i8]* @.str1, i32 0, i32 0)
$80 = void
(gdb) p (('llvm::Instruction'*)GV->use_back())
$81 = ('llvm::Instruction' *) 0x107279b88
(gdb) p (('llvm::Instruction'*)GV->use_back())->getParent()
$82 = (const 'llvm::BasicBlock' *) 0x6c675f7878630046

My conclusion was that the use chains weren't updated. Is there any recommended way of deleting a llvm::Function such that the use chain of the globals that it uses to be updated correspondingly?

Many thanks,
Vassil

#2

Hi,
  I have:
  ...
@.str1 = private unnamed_addr constant [21 x i8] c"Now f is a
function\0A\00", align 1
; Function Attrs: ssp uwtable
define i32 @_Z1fv() #2 {
entry:
  %call = call i32 (i8*, ...)* @printf(i8* getelementptr inbounds ([21 x
i8]* @.str1, i32 0, i32 0))
  ret i32 0
}

Then I get after trying to erase the function from the module:

511 GV->eraseFromParent();
(gdb) p GV->dump()

; Function Attrs: ssp uwtable
define i32 @_Z1fv() #2 {
entry:
  %call = call i32 (i8*, ...)* @printf(i8* getelementptr inbounds ([21 x
i8]* @.str1, i32 0, i32 0))
  ret i32 0
}

(gdb) n
513 }
(gdb) br llvm::AssemblyWriter::printModule(llvm::Module const*)
(gdb) p m_CurTransaction->getModule()->dump()
llvm::AssemblyWriter::printGlobal (this=0x7fff5fbfe850, GV=0x107274058) at
/Users/vvassilev/workspace/root/interpreter/llvm/src/lib/IR/AsmWriter.cpp:1444
1444 if (GV->isMaterializable())
(gdb) p GV->use_empty()
$78 = false
(gdb) p GV->use_back()
$79 = (class llvm::User *) 0x107279b88
(gdb) p GV->use_back()->dump()
i8* getelementptr inbounds ([21 x i8]* @.str1, i32 0, i32 0)
$80 = void
(gdb) p (('llvm::Instruction'*)GV->use_back())
$81 = ('llvm::Instruction' *) 0x107279b88
(gdb) p (('llvm::Instruction'*)GV->use_back())->getParent()
$82 = (const 'llvm::BasicBlock' *) 0x6c675f7878630046

My conclusion was that the use chains weren't updated. Is there any
recommended way of deleting a llvm::Function such that the use chain of the
globals that it uses to be updated correspondingly?

You probably want replaceAllUsesWith.

#3

Hi,
   I have:
   ...
@.str1 = private unnamed_addr constant [21 x i8] c"Now f is a
function\0A\00", align 1
; Function Attrs: ssp uwtable
define i32 @_Z1fv() #2 {
entry:
   %call = call i32 (i8*, ...)* @printf(i8* getelementptr inbounds ([21 x
i8]* @.str1, i32 0, i32 0))
   ret i32 0
}

Then I get after trying to erase the function from the module:

511 GV->eraseFromParent();
(gdb) p GV->dump()

; Function Attrs: ssp uwtable
define i32 @_Z1fv() #2 {
entry:
   %call = call i32 (i8*, ...)* @printf(i8* getelementptr inbounds ([21 x
i8]* @.str1, i32 0, i32 0))
   ret i32 0
}

(gdb) n
513 }
(gdb) br llvm::AssemblyWriter::printModule(llvm::Module const*)
(gdb) p m_CurTransaction->getModule()->dump()
llvm::AssemblyWriter::printGlobal (this=0x7fff5fbfe850, GV=0x107274058) at
/Users/vvassilev/workspace/root/interpreter/llvm/src/lib/IR/AsmWriter.cpp:1444
1444 if (GV->isMaterializable())
(gdb) p GV->use_empty()
$78 = false
(gdb) p GV->use_back()
$79 = (class llvm::User *) 0x107279b88
(gdb) p GV->use_back()->dump()
i8* getelementptr inbounds ([21 x i8]* @.str1, i32 0, i32 0)
$80 = void
(gdb) p (('llvm::Instruction'*)GV->use_back())
$81 = ('llvm::Instruction' *) 0x107279b88
(gdb) p (('llvm::Instruction'*)GV->use_back())->getParent()
$82 = (const 'llvm::BasicBlock' *) 0x6c675f7878630046

My conclusion was that the use chains weren't updated. Is there any
recommended way of deleting a llvm::Function such that the use chain of the
globals that it uses to be updated correspondingly?

You probably want replaceAllUsesWith.

I am sorry I don't understand. Are you suggesting calling replaceAllUses of the .str1? What I really want to do is to 'erase' the function. By erasing I'd expect the uses of .str1 to 0 (because in the example I have it is used only by f()) and I see they are not.
Vassil

#4

You probably want replaceAllUsesWith.

I am sorry I don't understand. Are you suggesting calling replaceAllUses of
the .str1? What I really want to do is to 'erase' the function. By erasing
I'd expect the uses of .str1 to 0 (because in the example I have it is used
only by f()) and I see they are not.

To remove something, the normal idiom is

Foo->replaceAllUsesWith(UndefValue::get(FooTy));
Foo->eraseFromParent();

Is that what you are trying to do?

Cheers,
Rafael

#5

You probably want replaceAllUsesWith.

I am sorry I don't understand. Are you suggesting calling replaceAllUses of
the .str1? What I really want to do is to 'erase' the function. By erasing
I'd expect the uses of .str1 to 0 (because in the example I have it is used
only by f()) and I see they are not.

To remove something, the normal idiom is

Foo->replaceAllUsesWith(UndefValue::get(FooTy));
Foo->eraseFromParent();

Is that what you are trying to do?

I want llvm to 'forget' already compiled and run function. Both from the ExecutionEngine/JIT and the llvm::Module. The problem using replaceAllUsesWith is that the JIT inserts a invisible use so that it can prevent from out-of-sync situations. I already tried using ExecutionContext::updateGlobalMapping and it doesn't help.
Vassil