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predict.c (estimate_probability): Added the pointer heuristic to the collection of static branch predictors.

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* predict.c (estimate_probability): Added the pointer heuristic to
        the collection of static branch predictors.

From-SVN: r32093
This commit is contained in:
Jason Eckhardt 2000-02-21 23:04:43 +00:00 committed by Jason Eckhardt
parent 1e387156a8
commit 24c3bf687d
2 changed files with 42 additions and 2 deletions
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5
gcc/ChangeLog
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@ -1,3 +1,8 @@
Mon Feb 21 17:06:27 2000 Jason Eckhardt <jle@cygnus.com>
* predict.c (estimate_probability): Added the pointer heuristic to
the collection of static branch predictors.
2000-02-21 Catherine Moore <clm@cygnus.com>
* config/mips/mips.h (ASM_SPEC): Add -mfix700.

39
gcc/predict.c
View File

@ -95,7 +95,10 @@ estimate_probability (loops_info)
}
}
/* Try to predict condjumps using same algorithm as mostly_true_jump. */
/* Attempt to predict conditional jumps using a number of heuristics.
For each conditional jump, we try each heuristic in a fixed order.
If more than one heuristic applies to a particular branch, the first
is used as the prediction for the branch. */
for (i = 0; i < n_basic_blocks - 1; i++)
{
rtx last_insn = BLOCK_END (i);
@ -108,7 +111,39 @@ estimate_probability (loops_info)
cond = get_condition (last_insn, &earliest);
if (! cond)
continue;
/* EQ tests are usually false and NE tests are usually true. Also,
/* Try "pointer heuristic."
A comparison ptr == 0 is predicted as false.
Similarly, a comparison ptr1 == ptr2 is predicted as false. */
prob = 0;
switch (GET_CODE (cond))
{
case EQ:
if (GET_CODE (XEXP (cond, 0)) == REG
&& REGNO_POINTER_FLAG (REGNO (XEXP (cond, 0)))
&& (XEXP (cond, 1) == const0_rtx
|| (GET_CODE (XEXP (cond, 1)) == REG
&& REGNO_POINTER_FLAG (REGNO (XEXP (cond, 1))))))
prob = REG_BR_PROB_BASE / 10;
break;
case NE:
if (GET_CODE (XEXP (cond, 0)) == REG
&& REGNO_POINTER_FLAG (REGNO (XEXP (cond, 0)))
&& (XEXP (cond, 1) == const0_rtx
|| (GET_CODE (XEXP (cond, 1)) == REG
&& REGNO_POINTER_FLAG (REGNO (XEXP (cond, 1))))))
prob = REG_BR_PROB_BASE / 2;
break;
default:
prob = 0;
}
if (prob && ! find_reg_note (last_insn, REG_BR_PROB, 0))
REG_NOTES (last_insn)
= gen_rtx_EXPR_LIST (REG_BR_PROB, GEN_INT (prob),
REG_NOTES (last_insn));
/* Try "opcode heuristic."
EQ tests are usually false and NE tests are usually true. Also,
most quantities are positive, so we can make the appropriate guesses
about signed comparisons against zero. */
switch (GET_CODE (cond))