[PATCH] Use new dump scheme for loop unroll passes

[Sharad Singhai <singhai at google dot com>]

Hi,

As per discussion in http://gcc.gnu.org/ml/gcc/2012-12/msg00056.html,
the attached patch updates loop unroll passes to use new dump
infrastructure.

This patch filters relevant dump messages into the following
three categories

- optimized: an optimization was successfully applied
- missed: an optimization was missed due to the described reason
- note: other relevant/detailed info during optimization. For example,
  loop unrolling computes the loop bounds and size.

Two sample outputs from one of the gcc tests (gcc.dg/unroll_1.c) are below.

Sample 1
-------------- info about optimized loops via
"-fopt-info-loop-optimized" -------
$ gcc gcc.dg/unroll_1.c -fno-diagnostics-show-caret -O2 -S
-fdump-rtl-loop2_unroll -funroll-loops -fopt-info-loop-optimized

Unrolled loop 1 completely (duplicated 2 times).
Exit condition of peeled iterations was eliminated.
Last iteration exit edge was proved true.
Unrolled loop 1 completely (duplicated 2 times).
Exit condition of peeled iterations was eliminated.
Last iteration exit edge was proved true.
--------------------------------

Sample 2:
--- All available loop optimization info, i.e., optimized+missed+note
via "-fopt-info-loop" ---
$ gcc gcc.dg/unroll_1.c -fno-diagnostics-show-caret -O2 -S
-fdump-rtl-loop2_unroll -funroll-loops -fopt-info-loop

Loop 1 iterates 2 times.
Loop 1 iterates at most 2 times.
Estimating sizes for loop 1
 BB: 4, after_exit: 0
  size:   2 if (i_1 <= 1)
   Exit condition will be eliminated in peeled copies.
 BB: 3, after_exit: 1
  size:   1 _5 = b[i_1];
  size:   1 _6 = _5 + 1;
  size:   1 a[i_1] = _6;
  size:   1 i_8 = i_1 + 1;
   Induction variable computation will be folded away.
size: 6-3, last_iteration: 2-0
  Loop size: 6
  Estimated size after unrolling: 5
Unrolled loop 1 completely (duplicated 2 times).
Exit condition of peeled iterations was eliminated.
Last iteration exit edge was proved true.
Forced exit to be taken: if (1 == 0)
Loop 1 iterates 2 times.
Loop 1 iterates at most 2 times.
Estimating sizes for loop 1
 BB: 4, after_exit: 0
  size:   2 if (i_1 <= 1)
   Exit condition will be eliminated in peeled copies.
 BB: 3, after_exit: 1
  size:   1 _4 = b[i_1];
  size:   1 _5 = _4 + 1;
  size:   1 a[i_1] = _5;
  size:   1 i_7 = i_1 + 1;
   Induction variable computation will be folded away.
size: 6-3, last_iteration: 2-0
  Loop size: 6
  Estimated size after unrolling: 5
Unrolled loop 1 completely (duplicated 2 times).
Exit condition of peeled iterations was eliminated.
Last iteration exit edge was proved true.
Forced exit to be taken: if (1 == 0)
--------------------------------

I would like to mention that this information is perhaps too verbose
and the the source location of optimized loops is not displayed. I can
add source line info (and fix up corresponding tests) if needed. But
right now I wanted to maintain current dump format faithfully. Perhaps
the format can be tweaked for better readability.

Note that all information dumped in response to -fopt-info is also
present in regular dump file(s) when corresponding dumps are
enabled. Thus in above examples, the loop optimization info is also
present in *.loop2_unroll dump file since the command line specified a
dump file via "-fdump-rtl-loop2_unroll" in addition to -fopt-info.

(As a side note, while doing the conversion, I found that the MSG_*
dump flags are unwieldy when used in conjunction with other
flags. Perhaps these flags should be renamed/shortened. I propose the following
       MSG_MISSED_OPTIMIZATION  ==> MSG_MISSED
       MSG_OPTIMIZED_LOCATIONS  ==> MSG_OPTIMIZED
But that is pure renaming and can be done separately.)

I have bootstrapped and tested this patch on x86_64 and found no new
failures. Okay for trunk?

Thanks,
Sharad

Attachment: unroll.opt_info.patch
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