the accumulator. If REUSE_EXPANSION is 0 reuse
the original accumulator. Else use
var_expansions[REUSE_EXPANSION - 1]. */
+ unsigned accum_pos; /* The position in which the accumulator is placed in
+ the insn src. For example in x = x + something
+ accum_pos is 0 while in x = something + x accum_pos
+ is 1. */
};
/* Information about optimization applied in
return NULL;
bb = split_edge (e);
emit_insn_after (insns, BB_END (bb));
- bb->flags |= BB_SUPERBLOCK;
+
+ /* ??? We used to assume that INSNS can contain control flow insns, and
+ that we had to try to find sub basic blocks in BB to maintain a valid
+ CFG. For this purpose we used to set the BB_SUPERBLOCK flag on BB
+ and call break_superblocks when going out of cfglayout mode. But it
+ turns out that this never happens; and that if it does ever happen,
+ the verify_flow_info call in loop_optimizer_finalize would fail.
+
+ There are two reasons why we expected we could have control flow insns
+ in INSNS. The first is when a comparison has to be done in parts, and
+ the second is when the number of iterations is computed for loops with
+ the number of iterations known at runtime. In both cases, test cases
+ to get control flow in INSNS appear to be impossible to construct:
+
+ * If do_compare_rtx_and_jump needs several branches to do comparison
+ in a mode that needs comparison by parts, we cannot analyze the
+ number of iterations of the loop, and we never get to unrolling it.
+
+ * The code in expand_divmod that was suspected to cause creation of
+ branching code seems to be only accessed for signed division. The
+ divisions used by # of iterations analysis are always unsigned.
+ Problems might arise on architectures that emits branching code
+ for some operations that may appear in the unroller (especially
+ for division), but we have no such architectures.
+
+ Considering all this, it was decided that we should for now assume
+ that INSNS can in theory contain control flow insns, but in practice
+ it never does. So we don't handle the theoretical case, and should
+ a real failure ever show up, we have a pretty good clue for how to
+ fix it. */
+
return bb;
}
static struct var_to_expand *
analyze_insn_to_expand_var (struct loop *loop, rtx insn)
{
- rtx set, dest, src, op1;
+ rtx set, dest, src, op1, op2, something;
struct var_to_expand *ves;
enum machine_mode mode1, mode2;
-
+ unsigned accum_pos;
+
set = single_set (insn);
if (!set)
return NULL;
if (!have_insn_for (GET_CODE (src), GET_MODE (src)))
return NULL;
- if (!XEXP (src, 0))
- return NULL;
-
op1 = XEXP (src, 0);
+ op2 = XEXP (src, 1);
if (!REG_P (dest)
&& !(GET_CODE (dest) == SUBREG
&& REG_P (SUBREG_REG (dest))))
return NULL;
- if (!rtx_equal_p (dest, op1))
- return NULL;
-
+ if (rtx_equal_p (dest, op1))
+ accum_pos = 0;
+ else if (rtx_equal_p (dest, op2))
+ accum_pos = 1;
+ else
+ return NULL;
+
+ /* The method of expansion that we are using; which includes
+ the initialization of the expansions with zero and the summation of
+ the expansions at the end of the computation will yield wrong results
+ for (x = something - x) thus avoid using it in that case. */
+ if (accum_pos == 1
+ && GET_CODE (src) == MINUS)
+ return NULL;
+
+ something = (accum_pos == 0)? op2 : op1;
+
if (!referenced_in_one_insn_in_loop_p (loop, dest))
return NULL;
- if (rtx_referenced_p (dest, XEXP (src, 1)))
+ if (rtx_referenced_p (dest, something))
return NULL;
mode1 = GET_MODE (dest);
- mode2 = GET_MODE (XEXP (src, 1));
+ mode2 = GET_MODE (something);
if ((FLOAT_MODE_P (mode1)
|| FLOAT_MODE_P (mode2))
&& !flag_unsafe_math_optimizations)
ves->op = GET_CODE (src);
ves->expansion_count = 0;
ves->reuse_expansion = 0;
+ ves->accum_pos = accum_pos;
return ves;
}
new_reg = get_expansion (ve);
validate_change (insn, &SET_DEST (set), new_reg, 1);
- validate_change (insn, &XEXP (SET_SRC (set), 0), new_reg, 1);
+ validate_change (insn, &XEXP (SET_SRC (set), ve->accum_pos), new_reg, 1);
if (apply_change_group ())
if (really_new_expansion)
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