On Thu, Jan 14, 2016 at 12:30 PM, Richard Biener <richard.guent...@gmail.com> wrote:
> > The vuse test is not necessary > >> + && (gimple_assign_rhs_code (def) == SSA_NAME >> + || is_gimple_min_invariant (gimple_assign_rhs1 (def)))) > > and the is_gimple_min_invariant (rhs1) test is not sufficient if you > consider - (-INT_MIN) with -ftrapv for example. Thanks, I didn't realize gimple_min_invariant would allow such cases. >> + /* Keep symbolic form, but look through obvious copies for constants. >> */ > > You're also looing for SSA names copied so the comment is sligntly wrong. So it occurs to me that we do only need to look for constants: picking one SSA name instead of another (when both are outside the loop) doesn't really help SCEV; and it seems safer/less change to avoid fiddling around with which names are used. Moreover, given we are in LC _SSA_, I think we can look through degenerate phi's even of SSA_NAMES, without violating loop-closed-ness, so long as we only use cases where we eventually reach a constant. Therefore, how about this version? (Bootstrapped + check-gcc + check-g++ on x86_64, AArch64, ARM; again, fixing vectorization of pr65947-2.c). If this is OK - that leaves only the first patch to SRA, https://gcc.gnu.org/ml/gcc-patches/2015-12/msg02117.html (the "extra" fixes I claimed in the guality testsuite were a testing mistake, but this version still fixes the regressions in guality pr54970.c from the original "ok with the comment added and a testcase (or two)" https://gcc.gnu.org/ml/gcc-patches/2015-11/msg01948.html, as well as the comment + 2*testcase). I think I'd still like to propose these as a stage 3/4 fix (with --param sra-max-scalarization-size-Ospeed=32) of PR/63679, a regression against gcc 4.9. Thanks, Alan gcc/ChangeLog: * tree-scalar-evolution.c (follow_copies_to_constant): New. (analyze_initial_condition, analyze_scalar_evolution_1): Call previous. --- gcc/tree-scalar-evolution.c | 50 ++++++++++++++++++++++++++++++--------------- 1 file changed, 33 insertions(+), 17 deletions(-) diff --git a/gcc/tree-scalar-evolution.c b/gcc/tree-scalar-evolution.c index 9b33693..470c3ea 100644 --- a/gcc/tree-scalar-evolution.c +++ b/gcc/tree-scalar-evolution.c @@ -1522,6 +1522,34 @@ analyze_evolution_in_loop (gphi *loop_phi_node, return evolution_function; } +/* Looks to see if VAR is a copy of a constant (via straightforward assignments + or degenerate phi's). If so, returns the constant; else, returns VAR. */ + +static tree +follow_copies_to_constant (tree var) +{ + tree res = var; + while (TREE_CODE (res) == SSA_NAME) + { + gimple *def = SSA_NAME_DEF_STMT (res); + if (gphi *phi = dyn_cast <gphi *> (def)) + { + if (tree rhs = degenerate_phi_result (phi)) + res = rhs; + else + break; + } + else if (gimple_assign_single_p (def)) + /* Will exit loop if not an SSA_NAME. */ + res = gimple_assign_rhs1 (def); + else + break; + } + if (CONSTANT_CLASS_P (res)) + return res; + return var; +} + /* Given a loop-phi-node, return the initial conditions of the variable on entry of the loop. When the CCP has propagated constants into the loop-phi-node, the initial condition is @@ -1574,21 +1602,9 @@ analyze_initial_condition (gphi *loop_phi_node) if (init_cond == chrec_not_analyzed_yet) init_cond = chrec_dont_know; - /* During early loop unrolling we do not have fully constant propagated IL. - Handle degenerate PHIs here to not miss important unrollings. */ - if (TREE_CODE (init_cond) == SSA_NAME) - { - gimple *def = SSA_NAME_DEF_STMT (init_cond); - if (gphi *phi = dyn_cast <gphi *> (def)) - { - tree res = degenerate_phi_result (phi); - if (res != NULL_TREE - /* Only allow invariants here, otherwise we may break - loop-closed SSA form. */ - && is_gimple_min_invariant (res)) - init_cond = res; - } - } + /* We may not have fully constant propagated IL. Handle degenerate PHIs here + to not miss important early loop unrollings. */ + init_cond = follow_copies_to_constant (init_cond); if (dump_file && (dump_flags & TDF_SCEV)) { @@ -1968,8 +1984,8 @@ analyze_scalar_evolution_1 (struct loop *loop, tree var, tree res) if (bb == NULL || !flow_bb_inside_loop_p (loop, bb)) { - /* Keep the symbolic form. */ - res = var; + /* Keep symbolic form, but look through obvious copies for constants. */ + res = follow_copies_to_constant (var); goto set_and_end; } -- 1.9.1
