Fix computation of number of iterations with unrolling
From-SVN: r44644
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@ -1,3 +1,8 @@
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2001-08-05 Bernd Schmidt <bernds@redhat.com>
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* doloop.c (doloop_modify_runtime): Properly compute number of
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iterations if loop was unrolled.
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2001-08-04 Hans-Peter Nilsson <hp@bitrange.com>
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* config/sh/sh.c (sh_asm_named_section): Fix typo in align
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79
gcc/doloop.c
79
gcc/doloop.c
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@ -567,17 +567,22 @@ doloop_modify_runtime (loop, iterations_max,
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|| comparison_code == NE);
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/* The number of iterations (prior to any loop unrolling) is given by:
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(abs (final - initial) + abs_inc - 1) / abs_inc.
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n = (abs (final - initial) + abs_inc - 1) / abs_inc.
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However, it is possible for the summation to overflow, and a
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safer method is:
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abs (final - initial) / abs_inc + (abs (final - initial) % abs_inc) != 0
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n = abs (final - initial) / abs_inc;
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n += (abs (final - initial) % abs_inc) != 0;
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If the loop has been unrolled, then the loop body has been
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preconditioned to iterate a multiple of unroll_number times.
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The number of iterations of the loop body is simply:
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abs (final - initial) / (abs_inc * unroll_number).
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preconditioned to iterate a multiple of unroll_number times. If
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abs_inc is != 1, the full calculation is
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t1 = abs_inc * unroll_number;
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n = abs (final - initial) / t1;
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n += (abs (final - initial) % t1) > t1 - abs_inc;
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The division and modulo operations can be avoided by requiring
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that the increment is a power of 2 (precondition_loop_p enforces
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@ -591,34 +596,38 @@ doloop_modify_runtime (loop, iterations_max,
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copy_rtx (neg_inc ? final_value : initial_value),
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NULL_RTX, unsigned_p, OPTAB_LIB_WIDEN);
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if (loop_info->unroll_number == 1)
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if (abs_inc * loop_info->unroll_number != 1)
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{
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int shift_count;
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rtx extra;
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rtx label;
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unsigned HOST_WIDE_INT limit;
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shift_count = exact_log2 (abs_inc * loop_info->unroll_number);
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if (shift_count < 0)
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abort ();
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/* abs (final - initial) / (abs_inc * unroll_number) */
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iterations = expand_binop (GET_MODE (diff), lshr_optab,
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diff, GEN_INT (shift_count),
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NULL_RTX, 1,
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OPTAB_LIB_WIDEN);
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if (abs_inc != 1)
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{
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int shift_count;
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rtx extra;
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rtx label;
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shift_count = exact_log2 (abs_inc);
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if (shift_count < 0)
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abort ();
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/* abs (final - initial) / abs_inc */
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iterations = expand_binop (GET_MODE (diff), lshr_optab,
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diff, GEN_INT (shift_count),
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NULL_RTX, 1,
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OPTAB_LIB_WIDEN);
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/* abs (final - initial) % abs_inc */
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/* abs (final - initial) % (abs_inc * unroll_number) */
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extra = expand_binop (GET_MODE (iterations), and_optab,
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diff, GEN_INT (abs_inc - 1),
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diff, GEN_INT (abs_inc * loop_info->unroll_number - 1),
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NULL_RTX, 1,
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OPTAB_LIB_WIDEN);
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/* If (abs (final - initial) % abs_inc == 0) jump past
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following increment instruction. */
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/* If (abs (final - initial) % (abs_inc * unroll_number)
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<= abs_inc * (unroll - 1)),
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jump past following increment instruction. */
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label = gen_label_rtx();
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emit_cmp_and_jump_insns (extra, const0_rtx, EQ, NULL_RTX,
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limit = abs_inc * (loop_info->unroll_number - 1);
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emit_cmp_and_jump_insns (extra, GEN_INT (limit),
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limit == 0 ? EQ : LEU, NULL_RTX,
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GET_MODE (extra), 0, 0, label);
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JUMP_LABEL (get_last_insn ()) = label;
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LABEL_NUSES (label)++;
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@ -631,27 +640,9 @@ doloop_modify_runtime (loop, iterations_max,
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emit_label (label);
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}
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else
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iterations = diff;
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}
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else
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{
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int shift_count;
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/* precondition_loop_p has preconditioned the loop so that the
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iteration count of the loop body is always a power of 2.
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Since we won't get an overflow calculating the loop count,
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the code we emit is simpler. */
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shift_count = exact_log2 (loop_info->unroll_number * abs_inc);
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if (shift_count < 0)
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abort ();
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iterations = expand_binop (GET_MODE (diff), lshr_optab,
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diff, GEN_INT (shift_count),
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NULL_RTX, 1,
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OPTAB_LIB_WIDEN);
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}
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iterations = diff;
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/* If there is a NOTE_INSN_LOOP_VTOP, we have a `for' or `while'
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style loop, with a loop exit test at the start. Thus, we can
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