From ec3fba5614d0ac97acf5a60164a4fdc0ad21791f Mon Sep 17 00:00:00 2001 From: Corey Minyard Date: Tue, 27 Nov 2001 18:30:40 +0000 Subject: [PATCH] unroll.c (loop_iterations): Detect one situation in which we overestimate the number of iterations. * unroll.c (loop_iterations): Detect one situation in which we overestimate the number of iterations. Co-Authored-By: Richard Henderson From-SVN: r47386 --- gcc/ChangeLog | 6 ++++++ gcc/unroll.c | 35 +++++++++++++++++++++++++++++++++++ 2 files changed, 41 insertions(+) diff --git a/gcc/ChangeLog b/gcc/ChangeLog index b118193aedb..00e613407a8 100644 --- a/gcc/ChangeLog +++ b/gcc/ChangeLog @@ -1,3 +1,9 @@ +2001-11-17 Corey Minyard + Richard Henderson + + * unroll.c (loop_iterations): Detect one situation in which we + overestimate the number of iterations. + 2001-11-27 Rainer Orth * gcc.c (set_input): Export. diff --git a/gcc/unroll.c b/gcc/unroll.c index 4b7dd974925..35ce939f012 100644 --- a/gcc/unroll.c +++ b/gcc/unroll.c @@ -3706,6 +3706,41 @@ loop_iterations (loop) if (initial_value == 0) return 0; + /* Some code transformations can result in code akin to + + tmp = i + 1; + ... + goto scan_start; + top: + tmp = tmp + 1; + scan_start: + i = tmp; + if (i < n) goto top; + + We'll have already detected this form of loop in scan_loop, + and set loop->top and loop->scan_start appropriately. + + In this situation, we skip the increment the first time through + the loop, which results in an incorrect estimate of the number + of iterations. Adjust the initial value to compensate. */ + + if (loop->scan_start && loop->cont + && INSN_LUID (loop->scan_start) < INSN_LUID (loop->cont) + && INSN_LUID (bl->biv->insn) < INSN_LUID (loop->scan_start)) + { + if (loop_dump_stream) + fprintf (loop_dump_stream, + "Loop iterations: Basic induction var skips initial incr.\n"); + if (GET_CODE (increment) != CONST_INT) + { + if (loop_dump_stream) + fprintf (loop_dump_stream, + "Loop iterations: Can't adjust with non-constant incr.\n"); + return 0; + } + initial_value = plus_constant (initial_value, -INTVAL (increment)); + } + unsigned_p = 0; off_by_one = 0; switch (comparison_code) -- 2.30.2