[llvm-dev] PGO question

Thu Mar 10 11:03:49 PST 2016

On Thu, Mar 10, 2016 at 10:01 AM, Toshio Suganuma <SUGANUMA at jp.ibm.com>
wrote:

> Hi David,
>
> Thank you for your reply. I tried both of the ways you suggested:
>
> 1) By specifying -instrprof for opt command, the IR level instrumentation
> seems to work ok.
> $ clang -c -o main.bc -O2 -m64 -emit-llvm main.c
> $ clang -c -o lbm.bc -O2 -m64 -emit-llvm lbm.c
> $ llvm-link -o _all_combined.bc lbm.bc main.bc
> $ opt -pgo-instr-gen -instrprof _all_combined.bc -o _all_combined_inst.bc
> $ clang -o lbm_inst _all_combined_inst.bc -O2 -m64 -lm
> -fprofile-instr-generate
>
> I found that the option -fprofile-instr-generate is still necessary in the
> link step, without which no profile data is produced (I confirmed it by
> ltrace).
>

yes -- it is needed as the driver needs to pass in the profile runtime
library to the linker -- which is signaled by the option.

> When using the resulting profile in opt command and printing call graphs,
> is it easy to set call edge counts from the profile data?
>
> $ opt -analyze -pgo-instr-use -print-callgraph _all_combined.bc
>
> Call graph node for function: 'main'<<0xb7635d60>> #uses=1
> CS<0xb764d420> calls function 'MAIN_parseCommandLine'
> CS<0xb764dd78> calls function 'printf'
> CS<0xb764de00> calls function 'MAIN_initialize'
> CS<0xb764e400> calls function 'LBM_handleInOutFlow'
> ...
>

There is no explicit way of doing this now -- especially for cg
post-inline. This is currently being worked on.

>
> 2) clang doesn't seem to accept -fprofile-instrument=llvm
> $ clang -fprofile-instr-generate -Xclang -fprofile-instrument=llvm main.c
> error: invalid PGO instrumentor in argument '-fprofile-instrument=llvm'
>
> This was added recently. You can update your clang/llvm source and rebuild
clang.

thanks,

David

> Thank you,
> --Toshio
>
> [image: Inactive hide details for Xinliang David Li ---2016/03/10
> 03:12:14---On Wed, Mar 9, 2016 at 9:45 AM, Toshio Suganuma via llvm-d]Xinliang
> David Li ---2016/03/10 03:12:14---On Wed, Mar 9, 2016 at 9:45 AM, Toshio
> Suganuma via llvm-dev < llvm-dev at lists.llvm.org> wrote:
>
> From: Xinliang David Li <xinliangli at gmail.com>
> To: Toshio Suganuma/Japan/IBM at IBMJP
> Cc: llvm-dev <llvm-dev at lists.llvm.org>, Rong Xu <xur at google.com>
> Date: 2016/03/10 03:12
> Subject: Re: [llvm-dev] PGO question
> ------------------------------
>
>
>
>
>
> On Wed, Mar 9, 2016 at 9:45 AM, Toshio Suganuma via llvm-dev <
> *llvm-dev at lists.llvm.org* <llvm-dev at lists.llvm.org>> wrote:
>
>    Hi,
>
>    I have a question regarding PGO.
>
>    I collected profile data with the instrumentation build
>    (-fprofile-instr-generate) and provided for PGO optimization in the second
>    build (with -fprofile-instr-use=xxx.profdata). This works fine.
>
>    Then I tried to provide the profile data to opt using the option
>    -pgo-instr-use, but this causes an error with the message: "Not an IR level
>    instrumentation profile".
>    I thought this error occurred because the profile data was produced by
>    the instrumentation build from the source level, not IR level.
>
>
>
> -fprofile-instr-generate by default still uses Clang frontend based
> instrumentation -- that is why you see the warning.
>
>
>    However, if I try to make -pgo-instr-gen for the opt command, the
>    resulting bitcode seems to cause a problem as follows (my environment is
>    3.9.0, mid Feb trunk).
>
>    $ clang -c -o main.bc -O2 -m64 -emit-llvm main.c
>    $ opt -pgo-instr-gen main.bc -o main_inst.bc
>
>
>
> you also need to use -instrprof to add the lowering pass.
>
> The formal way to enable IR level instrumentation is to use the following
> command line:
>
> clang -fprofile-instr-generate -Xclang -fprofile-instrument=llvm main.c
>
> David
>
>    $ llc main_inst.bc -o main_inst.s
>    instrprof failed to lower an increment
>    UNREACHABLE executed at
>    /home/suganuma/tools/llvm_new/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp:5245!
>    #0 0x00000000815ecc7a llvm::sys::PrintStackTrace(llvm::raw_ostream&)
>    /home/suganuma/tools/llvm_new/llvm/lib/Support/Unix/Signals.inc:322:0
>    #1 0x00000000815ed02a PrintStackTraceSignalHandler(void*)
>    /home/suganuma/tools/llvm_new/llvm/lib/Support/Unix/Signals.inc:380:0
>    #2 0x00000000815eb33e llvm::sys::RunSignalHandlers()
>    /home/suganuma/tools/llvm_new/llvm/lib/Support/Signals.cpp:44:0
>    ...
>    #7 0x0000000081577202
>    /home/suganuma/tools/llvm_new/llvm/lib/Support/ErrorHandling.cpp:117:0
>    #8 0x000000008139792a
>    llvm::SelectionDAGBuilder::visitIntrinsicCall(llvm::CallInst const&,
>    unsigned int)
>    /home/suganuma/tools/llvm_new/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp:5247:0
>    #9 0x000000008139b11c
>    llvm::SelectionDAGBuilder::visitCall(llvm::CallInst const&)
>    /home/suganuma/tools/llvm_new/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp:5811:0
>    #10 0x00000000813737e4 llvm::SelectionDAGBuilder::visit(unsigned int,
>    llvm::User const&)
>    /home/suganuma/tools/llvm_new/llvm/include/llvm/IR/Instruction.def:186:0
>    ...
>
>    Am I doing something wrong? How can we provide profile data to opt?
>    What actually I want to do is to dump call graph (cross module) and
>    cfg that reflect counter values from profile data.
>
>    Thank you,
>    --Toshio
>
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