[LLVMdev] llc is taking a long time at -O1 to convert *.bc to *.s

[Kodakara, Sreekumar V]

Hi All,

I am using llvm-3.0 release version for compiling some files. I have a cpp file on which I did a few custom passes. After that I used llc to convert the *.bc file to *.s file at -O1 optimization level. llc took ~2630 seconds to perform this conversion. I timed llc and these are the top three passes that is taking most of the time.

 ---User Time---   --System Time--   --User+System--   ---Wall Time---  --- Name ---
  1816.1735 ( 77.8%)  23.3215 ( 69.7%)  1839.4950 ( 77.6%)  1839.4132 ( 77.6%)  Simple Register Coalescing
  493.5948 ( 21.1%)   9.1846 ( 27.4%)  502.7794 ( 21.2%)  502.7681 ( 21.2%)  X86 DAG->DAG Instruction Selection
   5.7244 (  0.2%)   0.0000 (  0.0%)   5.7244 (  0.2%)   5.7204 (  0.2%)  Machine Instruction LICM

I am running this in a fairly new Xeon server. Furthermore, at -O0, llc takes less than 20 seconds to complete. Is this behavior expected and is there a way to disable Simple Register Coalescing pass without switching to -O0 optimization level to get around this problem?

Thanks
Sreekumar


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