[LLVMdev] Loading ProfileInfo in Backend. (Was: [PATCH] & Question: Preserving ProfileInfo for backend.)

[Andreas Neustifter]

Shuguang Feng wrote:
>> What does "llc -debug-pass=Structure" say? Is the ProfileLoaderPass
>> really the last pass to touch the ProfileInfo before you are using it?
> 
> Below is the sequence of passes that I see.  Although the
> NoProfileInfo pass is being run, it should be subsequently overridden
> by ProfileInfoLoaderPass (LoaderPass) correct?

Yes.

> Target Data Layout
> Create Garbage Collector Module Metadata
> Basic Alias Analysis (default AA impl)
> DWARF Information Writer
> No Profile Information
> Module Information
>   ModulePass Manager
>     FunctionPass Manager
>       Preliminary module verification
>       Dominator Tree Construction
>       Module Verifier
>       Natural Loop Construction
>       Canonicalize natural loops
>       Scalar Evolution Analysis
>       Loop Pass Manager
>         Loop Strength Reduction
>       Lower Garbage Collection Instructions
>       Remove unreachable blocks from the CFG
>       Optimize for code generation
>       Insert stack protectors
>       X86 DAG->DAG Instruction Selection
>       X86 FP_REG_KILL inserter
>       X86 Maximal Stack Alignment Calculator
>       <MY PASS RUNS HERE>
> 
> 
>> Also, does bb.getBasicBlock() for sure always returns a valid block
>> refrerence?
> 
> Yes. I am printing bb and *bb.getBasicBlock() in order to compare the
> contents of the IR in the BasicBlock and the target assembly in the
> MachineBasicBlock.
> 
>> You are getting the PI by getAnalysis<ProfileInfo>() I presume? Is this
>> really the instance created by ProfileLoaderPass?
> 
> Yes, I have "PI = &getAnalysis<ProfileInfo>()" in my code (modeled
> after BasicBlockPlacement.cpp).  However, when I run gdb the value of
> the Pass* pointer returned by createProfileLoaderPass() does not match
> the value of PI (of type ProfileInfo*) that I see inside my
> MachineFunctionPass.  The abbreviated output of gdb is found below:
> 
> Breakpoint 1, main (argc=11, argv=0xbfffd394) at <path to llvm>/tools/
> llc/llc.cpp:292
> 292	      Pass* tmp = createProfileLoaderPass();
> (gdb) p tmp
> $1 = (class llvm::Pass *) 0x3573000
> (gdb) c
> Continuing.
> 
> Breakpoint 2, main (argc=11, argv=0xbfffd394) at <path to llvm>/tools/
> llc/llc.cpp:293
> 293	      Passes.add(tmp);
> (gdb) p tmp
> $2 = (class llvm::Pass *) 0x8feeaf0
> 
> So the address of the ProfileLoaderPass should be 0x8feeaf0 correct?
> But I see the following inside my own pass:
> 
> Breakpoint 3, MyCodeGenPass::runOnMachineFunction (this=0x90be200,
> MF=@0x90ca280) at <path to llvm>/lib/Target/X86/MyCodeGenPass.cpp:108
> 108	                   <random line of code after PI =
> &getAnalysis<ProfileInfo>() executes>
> (gdb) p PI
> $3 = (class llvm::ProfileInfo *) 0x90be438

I *guess* this two pointer should point to the same object, this could
explain why the ProfileInfo you are reading is not the expected one. Can
anyone from the list confirm this?

It *is* allowed to access ModulePass analysis information from an
FunctionPass?

Can you try to manually override the PI value in the
MyCodeGenPass::runOnMachineFunction() to the value seen in llc and then
access the ProfileInfo?

>> (I guess for the last two questions its best to use gdb, are you
>> familiar with it?)
> 
> I have a working knowledge :) but haven't used any bells and whistles.

Worked fine enough!

Andi