diff options
author | rakdver <rakdver@138bc75d-0d04-0410-961f-82ee72b054a4> | 2007-04-17 16:42:29 +0000 |
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committer | rakdver <rakdver@138bc75d-0d04-0410-961f-82ee72b054a4> | 2007-04-17 16:42:29 +0000 |
commit | 25153338ebbedbe0f614bc9b994fa72c6fb38699 (patch) | |
tree | 0a31c59ebc8695e61c56119d3a3890c7117e0a43 /gcc/cfgloopanal.c | |
parent | b9c7fce7adefe388cca987a0633e2e80be25084e (diff) | |
download | gcc-25153338ebbedbe0f614bc9b994fa72c6fb38699.tar.gz |
PR rtl-optimization/31360
* cfgloopanal.c (target_small_cost, target_pres_cost): Removed.
(target_reg_cost): New.
(init_set_costs): Initialize target_reg_cost. Add comments
regarding the rationale of the costs.
(global_cost_for_size): Renamed to...
(estimate_reg_pressure_cost): ... and simplify. Decrease importance
of register pressure.
* tree-ssa-loop-ivopts.c (ivopts_global_cost_for_size): Use
estimate_reg_pressure_cost. Add number of ivs.
(determine_set_costs): Dump target_reg_cost.
* loop-invariant.c (gain_for_invariant): Use
estimate_reg_pressure_cost. Removed n_inv_uses argument.
(best_gain_for_invariant, find_invariants_to_move): Remove
n_inv_uses.
* cfgloop.h (target_small_cost, target_pres_cost): Removed.
(target_reg_cost): Declare.
(global_cost_for_size): Declaration removed.
(estimate_reg_pressure_cost): Declare.
* gcc.dg/loop-7.c: New test.
git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@123919 138bc75d-0d04-0410-961f-82ee72b054a4
Diffstat (limited to 'gcc/cfgloopanal.c')
-rw-r--r-- | gcc/cfgloopanal.c | 55 |
1 files changed, 31 insertions, 24 deletions
diff --git a/gcc/cfgloopanal.c b/gcc/cfgloopanal.c index 4612ab8f1a1..7baa30a4899 100644 --- a/gcc/cfgloopanal.c +++ b/gcc/cfgloopanal.c @@ -523,11 +523,13 @@ seq_cost (rtx seq) /* The properties of the target. */ unsigned target_avail_regs; /* Number of available registers. */ -unsigned target_res_regs; /* Number of reserved registers. */ -unsigned target_small_cost; /* The cost for register when there is a free one. */ -unsigned target_pres_cost; /* The cost for register when there are not too many - free ones. */ -unsigned target_spill_cost; /* The cost for register when we need to spill. */ +unsigned target_res_regs; /* Number of registers reserved for temporary + expressions. */ +unsigned target_reg_cost; /* The cost for register when there still + is some reserve, but we are approaching + the number of available registers. */ +unsigned target_spill_cost; /* The cost for register when we need + to spill. */ /* Initialize the constants for computing set costs. */ @@ -548,14 +550,20 @@ init_set_costs (void) target_res_regs = 3; - /* These are really just heuristic values. */ + /* Set up the costs for using extra registers: + + 1) If not many free registers remain, we should prefer having an + additional move to decreasing the number of available registers. + (TARGET_REG_COST). + 2) If no registers are available, we need to spill, which may require + storing the old value to memory and loading it back + (TARGET_SPILL_COST). */ start_sequence (); emit_move_insn (reg1, reg2); seq = get_insns (); end_sequence (); - target_small_cost = seq_cost (seq); - target_pres_cost = 2 * target_small_cost; + target_reg_cost = seq_cost (seq); start_sequence (); emit_move_insn (mem, reg1); @@ -565,27 +573,26 @@ init_set_costs (void) target_spill_cost = seq_cost (seq); } -/* Calculates cost for having SIZE new loop global variables. REGS_USED is the - number of global registers used in loop. N_USES is the number of relevant - variable uses. */ +/* Estimates cost of increased register pressure caused by making N_NEW new + registers live around the loop. N_OLD is the number of registers live + around the loop. */ unsigned -global_cost_for_size (unsigned size, unsigned regs_used, unsigned n_uses) +estimate_reg_pressure_cost (unsigned n_new, unsigned n_old) { - unsigned regs_needed = regs_used + size; - unsigned cost = 0; + unsigned regs_needed = n_new + n_old; + /* If we have enough registers, we should use them and not restrict + the transformations unnecessarily. */ if (regs_needed + target_res_regs <= target_avail_regs) - cost += target_small_cost * size; - else if (regs_needed <= target_avail_regs) - cost += target_pres_cost * size; - else - { - cost += target_pres_cost * size; - cost += target_spill_cost * n_uses * (regs_needed - target_avail_regs) / regs_needed; - } - - return cost; + return 0; + + /* If we are close to running out of registers, try to preserve them. */ + if (regs_needed <= target_avail_regs) + return target_reg_cost * n_new; + + /* If we run out of registers, it is very expensive to add another one. */ + return target_spill_cost * n_new; } /* Sets EDGE_LOOP_EXIT flag for all loop exits. */ |