[llvm-commits] [llvm] r156593 - in /llvm/trunk: docs/LangRef.html include/llvm/CodeGen/ISDOpcodes.h include/llvm/Intrinsics.td include/llvm/Target/TargetSelectionDAG.td lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp lib/CodeGen/SelectionDAG/SelectionDAGDumper.cpp lib/Target/X86/X86InstrSystem.td test/CodeGen/X86/trap.ll

[Nick Lewycky]

Dan Gohman wrote:
>
> On May 10, 2012, at 10:26 PM, Nick Lewycky wrote:
>
>> Dan Gohman wrote:
>>> Modified: llvm/trunk/docs/LangRef.html
>>> +<h5>Semantics:</h5>
>>> +<p>This intrinsic is lowered to code which is intended to cause an
>>> execution
>>> + trap with the intention of requesting the attention of a debugger.</p>
>>
>> ... but no other effect? Is that how it's different from @llvm.trap,
>> that if there is no debugger, the program continue running normally?
>
> The main difference is that on x86 it generates int3, rather than ud2.
> Perhaps I
> tried to hard to make the language generic.

Right, but I don't know what that does either. I know that ud2 is going 
to stop your program (signal handlers notwithstanding), but what does 
int 3 do? Call into the debugger if there is a debugger, otherwise the 
program trundles along? Or does it do the exact same thing as ud2? (In 
which case, what's the point of this new intrinsic?)

Nick