llvm dev - Jan 2009 - [LLVMdev] Load from abs address generated bad code on LLVM 2.4

Chris Lattner wrote:
> On Jan 20, 2009, at 2:10 AM, Andrew Haley wrote:
> 
>> Chris Lattner wrote:
>>> On Jan 19, 2009, at 7:55 AM, Andrew Haley wrote:
>>>
>>>> This is x86_64.  I have a problem where an absolute memory load
>>>> The current LLVM trunk does not have this bug.  This seems
quite a
>>>> nasty
>>>> bug; is there any chance of a bug-fix release for LLVM 2.4, or
>>>> should I
>>>> just use LLVM trunk until LLVM 2.5 ?
>>> As others have pointed out, using a global and addglobalmapping is
a
>>> great workaround for the problem.
>> Thanks.
>>
>>> We generally don't do "dot" releases, since we have a
short release
>>> cycle anyway.  The 2.5 release process is slated to start this
week.
>> Mmm, but the problem is that interfaces keep changing, so simply
>> upgrading to the latest release isn't possible.  Even the tiny
>> test case I posted doesn't work with the latest version: there
>> were changes needed to get it to compile.  Also, I can no longer
>> figure out how to turn on debugging dumps in the JIT.  The simple
>>
>>   DebugFlag = true;
>>   CurrentDebugType = "x86-emitter";
>>
>> no longer works, and there seems to be no replacement for it.
> 
> That should work fine, just use "jit" instead of
"x86-emitter" as the
> debug type.
That's impossible: CurrentDebugType is now private; it appears
nowhere in the installed headers.  I can't find any public interface
to allow a JIT to set it.

Andrew.

On Jan 21, 2009, at 4:15 AM, Andrew Haley wrote:
>> That should work fine, just use "jit" instead of
"x86-emitter" as the
>> debug type.
>
> That's impossible: CurrentDebugType is now private; it appears
> nowhere in the installed headers.  I can't find any public interface
> to allow a JIT to set it.
Ah ok.  I'd suggest doing what llvm-gcc does here, it is a much more  
stable API:

   std::vector<const char*> Args;
   Args.push_back(""); // program name
   Args.push_back("-debug-only=jit");
   ...
   Args.push_back(0);  // Null terminator.
   cl::ParseCommandLineOptions(Args.size()-1, (char**)&Args[0]);

This also gives you control over optimizations and codegen options,

-Chris

Chris Lattner wrote:
> On Jan 21, 2009, at 4:15 AM, Andrew Haley wrote:
>>> That should work fine, just use "jit" instead of
"x86-emitter" as the
>>> debug type.
>> That's impossible: CurrentDebugType is now private; it appears
>> nowhere in the installed headers.  I can't find any public
interface
>> to allow a JIT to set it.
> 
> Ah ok.  I'd suggest doing what llvm-gcc does here, it is a much more  
> stable API:
> 
>    std::vector<const char*> Args;
>    Args.push_back(""); // program name
>    Args.push_back("-debug-only=jit");
>    ...
>    Args.push_back(0);  // Null terminator.
>    cl::ParseCommandLineOptions(Args.size()-1, (char**)&Args[0]);
> 
> This also gives you control over optimizations and codegen options,
Yes, thanks.  It's a slightly weird hack, but it works perfectly.  :-)

"-debug-only=jit" generates just a binary dump, like this:

JIT: Binary code:
JIT: 00000000: 4a04b848 000000ca 048b0000 c320

whereas "-debug-only=x86-emitter" generates this:

%RAX<def> = MOV64ri <ga:poo1>
%EAX<def> = MOV32rm %RAX<kill>, 1, %reg0, 0, Mem:LD(4,4) [poo1 + 0]
RET %EAX<imp-use,kill>

which may be more useful.

Can I put in a request some machine-independent names for the debug
dumps?  It's "x86-emitter", "alpha-emitter",
"x86-codegen", and so on.
We'd have to put a big target-dependent switch statement in our code to
enable asm dumps.

Andrew.

Chris Lattner wrote:
> On Jan 21, 2009, at 4:15 AM, Andrew Haley wrote:
>>> That should work fine, just use "jit" instead of
"x86-emitter" as the
>>> debug type.
>> That's impossible: CurrentDebugType is now private; it appears
>> nowhere in the installed headers.  I can't find any public
interface
>> to allow a JIT to set it.
> 
> Ah ok.  I'd suggest doing what llvm-gcc does here, it is a much more  
> stable API:
> 
>    std::vector<const char*> Args;
>    Args.push_back(""); // program name
>    Args.push_back("-debug-only=jit");
>    ...
>    Args.push_back(0);  // Null terminator.
>    cl::ParseCommandLineOptions(Args.size()-1, (char**)&Args[0]);
> 
> This also gives you control over optimizations and codegen options,
Sadly, that doesn't work either.  Well, it works once, but then you
can't change it back.  We need something more like

--- ./lib/Support/Debug.cpp~    2009-01-23 12:15:27.000000000 +0000
+++ lib/Support/Debug.cpp       2009-01-23 12:15:53.000000000 +0000
@@ -48,7 +48,7 @@
   static cl::opt<DebugOnlyOpt, true, cl::parser<std::string> >
   DebugOnly("debug-only", cl::desc("Enable a specific type of
debug output"),
             cl::Hidden, cl::value_desc("debug string"),
-            cl::location(DebugOnlyOptLoc), cl::ValueRequired);
+            cl::location(DebugOnlyOptLoc), cl::ValueRequired, cl::ZeroOrMore);
 #endif
 }


to allow it to be dynamically used by a JIT.  Of course, with a large program
being JITted it's really important to be able just to use debugging exactly
where you need it.

Andrew.