[PATCH] divmod: Match and expand DIVMOD even in some cases of constant divisor [PR97282]
Christophe Lyon
christophe.lyon@linaro.org
Tue Oct 6 09:42:08 GMT 2020
Hi Jakub,
On Tue, 6 Oct 2020 at 10:13, Richard Biener <rguenther@suse.de> wrote:
>
> On Tue, 6 Oct 2020, Jakub Jelinek wrote:
>
> > Hi!
> >
> > As written in the comment, tree-ssa-math-opts.c wouldn't create a DIVMOD
> > ifn call for division + modulo by constant for the fear that during
> > expansion we could generate better code for those cases.
> > If the divisoris a power of two, that is certainly the case always,
> > but otherwise expand_divmod can punt in many cases, e.g. if the division
> > type's precision is above HOST_BITS_PER_WIDE_INT, we don't even call
> > choose_multiplier, because it works on HOST_WIDE_INTs (true, something
> > we should fix eventually now that we have wide_ints), or if pre/post shift
> > is larger than BITS_PER_WORD.
> >
> > So, the following patch recognizes DIVMOD with constant last argument even
> > when it is unclear if expand_divmod will be able to optimize it, and then
> > during DIVMOD expansion if the divisor is constant attempts to expand it as
> > division + modulo and if they actually don't contain any libcalls or
> > division/modulo, they are kept as is, otherwise that sequence is thrown away
> > and divmod optab or libcall is used.
> >
> > Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
>
> OK.
>
> Richard.
>
> > 2020-10-06 Jakub Jelinek <jakub@redhat.com>
> >
> > PR rtl-optimization/97282
> > * tree-ssa-math-opts.c (divmod_candidate_p): Don't return false for
> > constant op2 if it is not a power of two and the type has precision
> > larger than HOST_BITS_PER_WIDE_INT or BITS_PER_WORD.
> > * internal-fn.c (contains_call_div_mod): New function.
> > (expand_DIVMOD): If last argument is a constant, try to expand it as
> > TRUNC_DIV_EXPR followed by TRUNC_MOD_EXPR, but if the sequence
> > contains any calls or {,U}{DIV,MOD} rtxes, throw it away and use
> > divmod optab or divmod libfunc.
> >
This patch causes ICEs on arm while building newlib or glibc
For instance with newlib when compiling vfwprintf.o:
during RTL pass: expand
In file included from
/tmp/1435347_7.tmpdir/aci-gcc-fsf/sources/newlib/newlib/libc/stdio/vfprintf.c:153:
/tmp/1435347_7.tmpdir/aci-gcc-fsf/sources/newlib/newlib/libc/include/stdio.h:
In function '_vfprintf_r':
/tmp/1435347_7.tmpdir/aci-gcc-fsf/sources/newlib/newlib/libc/include/stdio.h:503:9:
internal compiler error: in int_mode_for_mode, at stor-layout.c:404
503 | int _vfprintf_r (struct _reent *, FILE *__restrict, const
char *__restrict, __VALIST)
| ^~~~~~~~~~~
0xaed4e3 int_mode_for_mode(machine_mode)
/tmp/1435347_7.tmpdir/aci-gcc-fsf/sources/gcc-fsf/gccsrc/gcc/stor-layout.c:404
0x7ff73d emit_move_via_integer
/tmp/1435347_7.tmpdir/aci-gcc-fsf/sources/gcc-fsf/gccsrc/gcc/expr.c:3425
0x808f2d emit_move_insn_1(rtx_def*, rtx_def*)
/tmp/1435347_7.tmpdir/aci-gcc-fsf/sources/gcc-fsf/gccsrc/gcc/expr.c:3793
0x8092d7 emit_move_insn(rtx_def*, rtx_def*)
/tmp/1435347_7.tmpdir/aci-gcc-fsf/sources/gcc-fsf/gccsrc/gcc/expr.c:3935
0x6e703f emit_library_call_value_1(int, rtx_def*, rtx_def*,
libcall_type, machine_mode, int, std::pair<rtx_def*, machine_mode>*)
/tmp/1435347_7.tmpdir/aci-gcc-fsf/sources/gcc-fsf/gccsrc/gcc/calls.c:5601
0xdff642 emit_library_call_value
/tmp/1435347_7.tmpdir/aci-gcc-fsf/sources/gcc-fsf/gccsrc/gcc/rtl.h:4258
0xdff642 arm_expand_divmod_libfunc
/tmp/1435347_7.tmpdir/aci-gcc-fsf/sources/gcc-fsf/gccsrc/gcc/config/arm/arm.c:33256
0x8c69af expand_DIVMOD
/tmp/1435347_7.tmpdir/aci-gcc-fsf/sources/gcc-fsf/gccsrc/gcc/internal-fn.c:3084
0x7021b7 expand_call_stmt
/tmp/1435347_7.tmpdir/aci-gcc-fsf/sources/gcc-fsf/gccsrc/gcc/cfgexpand.c:2612
0x7021b7 expand_gimple_stmt_1
/tmp/1435347_7.tmpdir/aci-gcc-fsf/sources/gcc-fsf/gccsrc/gcc/cfgexpand.c:3686
0x7021b7 expand_gimple_stmt
/tmp/1435347_7.tmpdir/aci-gcc-fsf/sources/gcc-fsf/gccsrc/gcc/cfgexpand.c:3851
0x702cfd expand_gimple_basic_block
/tmp/1435347_7.tmpdir/aci-gcc-fsf/sources/gcc-fsf/gccsrc/gcc/cfgexpand.c:5892
0x70533e execute
/tmp/1435347_7.tmpdir/aci-gcc-fsf/sources/gcc-fsf/gccsrc/gcc/cfgexpand.c:6576
Christophe
> > * gcc.target/i386/pr97282.c: New test.
> >
> > --- gcc/tree-ssa-math-opts.c.jj 2020-10-01 10:40:10.104755999 +0200
> > +++ gcc/tree-ssa-math-opts.c 2020-10-05 13:51:54.476628287 +0200
> > @@ -3567,9 +3567,24 @@ divmod_candidate_p (gassign *stmt)
> >
> > /* Disable the transform if either is a constant, since division-by-constant
> > may have specialized expansion. */
> > - if (CONSTANT_CLASS_P (op1) || CONSTANT_CLASS_P (op2))
> > + if (CONSTANT_CLASS_P (op1))
> > return false;
> >
> > + if (CONSTANT_CLASS_P (op2))
> > + {
> > + if (integer_pow2p (op2))
> > + return false;
> > +
> > + if (TYPE_PRECISION (type) <= HOST_BITS_PER_WIDE_INT
> > + && TYPE_PRECISION (type) <= BITS_PER_WORD)
> > + return false;
> > +
> > + /* If the divisor is not power of 2 and the precision wider than
> > + HWI, expand_divmod punts on that, so in that case it is better
> > + to use divmod optab or libfunc. Similarly if choose_multiplier
> > + might need pre/post shifts of BITS_PER_WORD or more. */
> > + }
> > +
> > /* Exclude the case where TYPE_OVERFLOW_TRAPS (type) as that should
> > expand using the [su]divv optabs. */
> > if (TYPE_OVERFLOW_TRAPS (type))
> > --- gcc/internal-fn.c.jj 2020-10-02 10:36:43.272290992 +0200
> > +++ gcc/internal-fn.c 2020-10-05 15:15:12.498349327 +0200
> > @@ -50,6 +50,7 @@ along with GCC; see the file COPYING3.
> > #include "tree-phinodes.h"
> > #include "ssa-iterators.h"
> > #include "explow.h"
> > +#include "rtl-iter.h"
> >
> > /* The names of each internal function, indexed by function number. */
> > const char *const internal_fn_name_array[] = {
> > @@ -2985,6 +2986,32 @@ expand_gather_load_optab_fn (internal_fn
> > emit_move_insn (lhs_rtx, ops[0].value);
> > }
> >
> > +/* Helper for expand_DIVMOD. Return true if the sequence starting with
> > + INSN contains any call insns or insns with {,U}{DIV,MOD} rtxes. */
> > +
> > +static bool
> > +contains_call_div_mod (rtx_insn *insn)
> > +{
> > + subrtx_iterator::array_type array;
> > + for (; insn; insn = NEXT_INSN (insn))
> > + if (CALL_P (insn))
> > + return true;
> > + else if (INSN_P (insn))
> > + FOR_EACH_SUBRTX (iter, array, PATTERN (insn), NONCONST)
> > + switch (GET_CODE (*iter))
> > + {
> > + case CALL:
> > + case DIV:
> > + case UDIV:
> > + case MOD:
> > + case UMOD:
> > + return true;
> > + default:
> > + break;
> > + }
> > + return false;
> > + }
> > +
> > /* Expand DIVMOD() using:
> > a) optab handler for udivmod/sdivmod if it is available.
> > b) If optab_handler doesn't exist, generate call to
> > @@ -3007,10 +3034,44 @@ expand_DIVMOD (internal_fn, gcall *call_
> > rtx op1 = expand_normal (arg1);
> > rtx target = expand_expr (lhs, NULL_RTX, VOIDmode, EXPAND_WRITE);
> >
> > - rtx quotient, remainder, libfunc;
> > + rtx quotient = NULL_RTX, remainder = NULL_RTX;
> > + rtx_insn *insns = NULL;
> > +
> > + if (TREE_CODE (arg1) == INTEGER_CST)
> > + {
> > + /* For DIVMOD by integral constants, there could be efficient code
> > + expanded inline e.g. using shifts and plus/minus. Try to expand
> > + the division and modulo and if it emits any library calls or any
> > + {,U}{DIV,MOD} rtxes throw it away and use a divmod optab or
> > + divmod libcall. */
> > + struct separate_ops ops;
> > + ops.code = TRUNC_DIV_EXPR;
> > + ops.type = type;
> > + ops.op0 = make_tree (ops.type, op0);
> > + ops.op1 = arg1;
> > + ops.op2 = NULL_TREE;
> > + ops.location = gimple_location (call_stmt);
> > + start_sequence ();
> > + quotient = expand_expr_real_2 (&ops, NULL_RTX, mode, EXPAND_NORMAL);
> > + if (contains_call_div_mod (get_insns ()))
> > + quotient = NULL_RTX;
> > + else
> > + {
> > + ops.code = TRUNC_MOD_EXPR;
> > + remainder = expand_expr_real_2 (&ops, NULL_RTX, mode, EXPAND_NORMAL);
> > + if (contains_call_div_mod (get_insns ()))
> > + remainder = NULL_RTX;
> > + }
> > + if (remainder)
> > + insns = get_insns ();
> > + end_sequence ();
> > + }
> > +
> > + if (remainder)
> > + emit_insn (insns);
> >
> > /* Check if optab_handler exists for divmod_optab for given mode. */
> > - if (optab_handler (tab, mode) != CODE_FOR_nothing)
> > + else if (optab_handler (tab, mode) != CODE_FOR_nothing)
> > {
> > quotient = gen_reg_rtx (mode);
> > remainder = gen_reg_rtx (mode);
> > @@ -3018,7 +3079,7 @@ expand_DIVMOD (internal_fn, gcall *call_
> > }
> >
> > /* Generate call to divmod libfunc if it exists. */
> > - else if ((libfunc = optab_libfunc (tab, mode)) != NULL_RTX)
> > + else if (rtx libfunc = optab_libfunc (tab, mode))
> > targetm.expand_divmod_libfunc (libfunc, mode, op0, op1,
> > "ient, &remainder);
> >
> > --- gcc/testsuite/gcc.target/i386/pr97282.c.jj 2020-10-05 15:31:19.500363710 +0200
> > +++ gcc/testsuite/gcc.target/i386/pr97282.c 2020-10-05 15:28:51.864499619 +0200
> > @@ -0,0 +1,25 @@
> > +/* PR rtl-optimization/97282 */
> > +/* { dg-do compile } */
> > +/* { dg-options "-O2" } */
> > +/* { dg-final { scan-assembler "call\[^\n\r]*__udivmod\[dt]i4" } } */
> > +
> > +#ifdef __SIZEOF_INT128__
> > +typedef __uint128_t T;
> > +#else
> > +typedef unsigned long long T;
> > +#endif
> > +
> > +unsigned long
> > +foo (T x)
> > +{
> > + if (x == 0)
> > + return 0;
> > +
> > + unsigned long ret = 0;
> > + while (x > 0)
> > + {
> > + ret = ret + x % 10;
> > + x = x / 10;
> > + }
> > + return ret;
> > +}
> >
> > Jakub
> >
> >
>
> --
> Richard Biener <rguenther@suse.de>
> SUSE Software Solutions Germany GmbH, Maxfeldstrasse 5, 90409 Nuernberg,
> Germany; GF: Felix Imend
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