diff options
Diffstat (limited to 'gcc')
| -rw-r--r-- | gcc/ChangeLog | 7 | ||||
| -rw-r--r-- | gcc/expmed.c | 25 |
2 files changed, 31 insertions, 1 deletions
diff --git a/gcc/ChangeLog b/gcc/ChangeLog index 46f3360..92a4d69 100644 --- a/gcc/ChangeLog +++ b/gcc/ChangeLog @@ -1,3 +1,10 @@ +2004-06-30 Roger Sayle <roger@eyesopen.com> + + * expmed.c (expand_shift): Consider expanding LSHIFT_EXPR by a + constant as a sequence of additions depending upon the rtx_costs. + (synth_mult): Update the "observed" cost of a shift, based upon + the above optimization. + 2004-06-28 Geoffrey Keating <geoffk@apple.com> Andreas Tobler <a.tobler@schweiz.ch> diff --git a/gcc/expmed.c b/gcc/expmed.c index a2278b9..e95a626 100644 --- a/gcc/expmed.c +++ b/gcc/expmed.c @@ -2017,6 +2017,24 @@ expand_shift (enum tree_code code, enum machine_mode mode, rtx shifted, if (op1 == const0_rtx) return shifted; + /* Check whether its cheaper to implement a left shift by a constant + bit count by a sequence of additions. */ + if (code == LSHIFT_EXPR + && GET_CODE (op1) == CONST_INT + && INTVAL (op1) > 0 + && INTVAL (op1) < GET_MODE_BITSIZE (mode) + && shift_cost[mode][INTVAL (op1)] > INTVAL (op1) * add_cost[mode]) + { + int i; + for (i = 0; i < INTVAL (op1); i++) + { + temp = force_reg (mode, shifted); + shifted = expand_binop (mode, add_optab, temp, temp, NULL_RTX, + unsignedp, OPTAB_LIB_WIDEN); + } + return shifted; + } + for (try = 0; temp == 0 && try < 3; try++) { enum optab_methods methods; @@ -2242,7 +2260,12 @@ synth_mult (struct algorithm *alg_out, unsigned HOST_WIDE_INT t, if (m < maxm) { q = t >> m; - cost = shift_cost[mode][m]; + /* The function expand_shift will choose between a shift and + a sequence of additions, so the observed cost is given as + MIN (m * add_cost[mode], shift_cost[mode][m]). */ + cost = m * add_cost[mode]; + if (shift_cost[mode][m] < cost) + cost = shift_cost[mode][m]; synth_mult (alg_in, q, cost_limit - cost, mode); cost += alg_in->cost; |