diff options
| -rw-r--r-- | gcc/ChangeLog | 5 | ||||
| -rw-r--r-- | gcc/predict.c | 39 |
2 files changed, 42 insertions, 2 deletions
diff --git a/gcc/ChangeLog b/gcc/ChangeLog index 3378818..f6e5897 100644 --- a/gcc/ChangeLog +++ b/gcc/ChangeLog @@ -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. diff --git a/gcc/predict.c b/gcc/predict.c index d8a588f..2cae39a 100644 --- a/gcc/predict.c +++ b/gcc/predict.c @@ -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)) |