diff options
Diffstat (limited to 'gcc/loop.c')
| -rw-r--r-- | gcc/loop.c | 46 |
1 files changed, 38 insertions, 8 deletions
@@ -293,7 +293,7 @@ static void record_giv (const struct loop *, struct induction *, rtx, rtx, rtx, rtx, rtx, rtx, int, enum g_types, int, int, rtx *); static void update_giv_derive (const struct loop *, rtx); -static void check_ext_dependent_givs (struct iv_class *, struct loop_info *); +static void check_ext_dependent_givs (const struct loop *, struct iv_class *); static int basic_induction_var (const struct loop *, rtx, enum machine_mode, rtx, rtx, rtx *, rtx *, rtx **); static rtx simplify_giv_expr (const struct loop *, rtx, rtx *, int *); @@ -5143,7 +5143,7 @@ strength_reduce (struct loop *loop, int flags) /* Check each extension dependent giv in this class to see if its root biv is safe from wrapping in the interior mode. */ - check_ext_dependent_givs (bl, loop_info); + check_ext_dependent_givs (loop, bl); /* Combine all giv's for this iv_class. */ combine_givs (regs, bl); @@ -7286,8 +7286,9 @@ combine_givs_p (struct induction *g1, struct induction *g2) make the giv illegal. */ static void -check_ext_dependent_givs (struct iv_class *bl, struct loop_info *loop_info) +check_ext_dependent_givs (const struct loop *loop, struct iv_class *bl) { + struct loop_info *loop_info = LOOP_INFO (loop); int ze_ok = 0, se_ok = 0, info_ok = 0; enum machine_mode biv_mode = GET_MODE (bl->biv->src_reg); HOST_WIDE_INT start_val; @@ -7298,9 +7299,6 @@ check_ext_dependent_givs (struct iv_class *bl, struct loop_info *loop_info) /* Make sure the iteration data is available. We must have constants in order to be certain of no overflow. */ - /* ??? An unknown iteration count with an increment of +-1 - combined with friendly exit tests of against an invariant - value is also amenable to optimization. Not implemented. */ if (loop_info->n_iterations > 0 && bl->initial_value && GET_CODE (bl->initial_value) == CONST_INT @@ -7367,6 +7365,37 @@ check_ext_dependent_givs (struct iv_class *bl, struct loop_info *loop_info) } } + /* If we know the BIV is compared at run-time against an + invariant value, and the increment is +/- 1, we may also + be able to prove that the BIV cannot overflow. */ + else if (bl->biv->src_reg == loop_info->iteration_var + && loop_info->comparison_value + && loop_invariant_p (loop, loop_info->comparison_value) + && (incr = biv_total_increment (bl)) + && GET_CODE (incr) == CONST_INT) + { + /* If the increment is +1, and the exit test is a <, + the BIV cannot overflow. (For <=, we have the + problematic case that the comparison value might + be the maximum value of the range.) */ + if (INTVAL (incr) == 1) + { + if (loop_info->comparison_code == LT) + se_ok = ze_ok = 1; + else if (loop_info->comparison_code == LTU) + ze_ok = 1; + } + + /* Likewise for increment -1 and exit test >. */ + if (INTVAL (incr) == -1) + { + if (loop_info->comparison_code == GT) + se_ok = ze_ok = 1; + else if (loop_info->comparison_code == GTU) + ze_ok = 1; + } + } + /* Invalidate givs that fail the tests. */ for (v = bl->giv; v; v = v->next_iv) if (v->ext_dependent) @@ -7388,8 +7417,9 @@ check_ext_dependent_givs (struct iv_class *bl, struct loop_info *loop_info) signed or unsigned, so to safely truncate we must satisfy both. The initial check here verifies the BIV itself; once that is successful we may check its range wrt the - derived GIV. */ - if (se_ok && ze_ok) + derived GIV. This works only if we were able to determine + constant start and end values above. */ + if (se_ok && ze_ok && info_ok) { enum machine_mode outer_mode = GET_MODE (v->ext_dependent); unsigned HOST_WIDE_INT max = GET_MODE_MASK (outer_mode) >> 1; |