Re: [PATCH] RISC-V: Fix bad insn splits with paradoxical subregs.

[Richard Biener <rguenther at suse dot de>]

On Wed, 18 Sep 2019, Kito Cheng wrote:

> Hi Jakub, Richard:
> 
> This commit is fixing wrong code gen for RISC-V, does it OK to
> backport to GCC 9 branch?

Since it is target specific and for non-primary/secondary targets
it's the RISC-V maintainers call whether to allow backporting this.
Generally wrong-code issues can be backported even if they are not
regressions if the chance they introduce other issues is low.

Richard.

> On Fri, Sep 6, 2019 at 4:34 AM Jim Wilson <jimw@sifive.com> wrote:
> >
> > Shifting by more than the size of a SUBREG_REG doesn't work, so we either
> > need to disable splits if an input is paradoxical, or else we need to
> > generate a clean temporary for intermediate results.
> >
> > This was tested with rv32i/newlib and rv64gc/linux cross builds and checks.
> > There were no regressions.  The new pr91635.c testcase works with the patch
> > and fails without it.  Also, code size for libc and libstdc++ was checked
> > and is smaller or equal sized with the patch, ignoring alignment padding.
> > The shift-shift-4.c testcase gives better code size with this patch.
> > The shift-shift-5.c testcase gave worse code size with a draft version
> > of this patch and is OK with the final version of this patch.
> >
> > Jakub wrote the first version of this patch, so gets primary credit for it.
> >
> > Committed.
> >
> > Jim
> >
> >         gcc/
> >         PR target/91635
> >         * config/riscv/riscv.md (zero_extendsidi2, zero_extendhi<GPR:mode>2,
> >         extend<SHORT:mode><SUPERQI:mode>2): Don't split if
> >         paradoxical_subreg_p (operands[0]).
> >         (*lshrsi3_zero_extend_3+1, *lshrsi3_zero_extend_3+2): Add clobber and
> >         use as intermediate value.
> >
> >         gcc/testsuite/
> >         PR target/91635
> >         * gcc.c-torture/execute/pr91635.c: New test.
> >         * gcc.target/riscv/shift-shift-4.c: New test.
> >         * gcc.target/riscv/shift-shift-5.c: New test.
> > ---
> >  gcc/config/riscv/riscv.md                     | 30 +++++++---
> >  gcc/testsuite/gcc.c-torture/execute/pr91635.c | 57 +++++++++++++++++++
> >  .../gcc.target/riscv/shift-shift-4.c          | 13 +++++
> >  .../gcc.target/riscv/shift-shift-5.c          | 16 ++++++
> >  4 files changed, 107 insertions(+), 9 deletions(-)
> >  create mode 100644 gcc/testsuite/gcc.c-torture/execute/pr91635.c
> >  create mode 100644 gcc/testsuite/gcc.target/riscv/shift-shift-4.c
> >  create mode 100644 gcc/testsuite/gcc.target/riscv/shift-shift-5.c
> >
> > diff --git a/gcc/config/riscv/riscv.md b/gcc/config/riscv/riscv.md
> > index 78260fcf6fd..744a027a1b7 100644
> > --- a/gcc/config/riscv/riscv.md
> > +++ b/gcc/config/riscv/riscv.md
> > @@ -1051,7 +1051,9 @@
> >    "@
> >     #
> >     lwu\t%0,%1"
> > -  "&& reload_completed && REG_P (operands[1])"
> > +  "&& reload_completed
> > +   && REG_P (operands[1])
> > +   && !paradoxical_subreg_p (operands[0])"
> >    [(set (match_dup 0)
> >         (ashift:DI (match_dup 1) (const_int 32)))
> >     (set (match_dup 0)
> > @@ -1068,7 +1070,9 @@
> >    "@
> >     #
> >     lhu\t%0,%1"
> > -  "&& reload_completed && REG_P (operands[1])"
> > +  "&& reload_completed
> > +   && REG_P (operands[1])
> > +   && !paradoxical_subreg_p (operands[0])"
> >    [(set (match_dup 0)
> >         (ashift:GPR (match_dup 1) (match_dup 2)))
> >     (set (match_dup 0)
> > @@ -1117,7 +1121,9 @@
> >    "@
> >     #
> >     l<SHORT:size>\t%0,%1"
> > -  "&& reload_completed && REG_P (operands[1])"
> > +  "&& reload_completed
> > +   && REG_P (operands[1])
> > +   && !paradoxical_subreg_p (operands[0])"
> >    [(set (match_dup 0) (ashift:SI (match_dup 1) (match_dup 2)))
> >     (set (match_dup 0) (ashiftrt:SI (match_dup 0) (match_dup 2)))]
> >  {
> > @@ -1766,15 +1772,20 @@
> >  ;; Handle AND with 2^N-1 for N from 12 to XLEN.  This can be split into
> >  ;; two logical shifts.  Otherwise it requires 3 instructions: lui,
> >  ;; xor/addi/srli, and.
> > +
> > +;; Generating a temporary for the shift output gives better combiner results;
> > +;; and also fixes a problem where op0 could be a paradoxical reg and shifting
> > +;; by amounts larger than the size of the SUBREG_REG doesn't work.
> >  (define_split
> >    [(set (match_operand:GPR 0 "register_operand")
> >         (and:GPR (match_operand:GPR 1 "register_operand")
> > -                (match_operand:GPR 2 "p2m1_shift_operand")))]
> > +                (match_operand:GPR 2 "p2m1_shift_operand")))
> > +   (clobber (match_operand:GPR 3 "register_operand"))]
> >    ""
> > - [(set (match_dup 0)
> > + [(set (match_dup 3)
> >         (ashift:GPR (match_dup 1) (match_dup 2)))
> >    (set (match_dup 0)
> > -       (lshiftrt:GPR (match_dup 0) (match_dup 2)))]
> > +       (lshiftrt:GPR (match_dup 3) (match_dup 2)))]
> >  {
> >    /* Op2 is a VOIDmode constant, so get the mode size from op1.  */
> >    operands[2] = GEN_INT (GET_MODE_BITSIZE (GET_MODE (operands[1]))
> > @@ -1786,12 +1797,13 @@
> >  (define_split
> >    [(set (match_operand:DI 0 "register_operand")
> >         (and:DI (match_operand:DI 1 "register_operand")
> > -               (match_operand:DI 2 "high_mask_shift_operand")))]
> > +               (match_operand:DI 2 "high_mask_shift_operand")))
> > +   (clobber (match_operand:DI 3 "register_operand"))]
> >    "TARGET_64BIT"
> > -  [(set (match_dup 0)
> > +  [(set (match_dup 3)
> >         (lshiftrt:DI (match_dup 1) (match_dup 2)))
> >     (set (match_dup 0)
> > -       (ashift:DI (match_dup 0) (match_dup 2)))]
> > +       (ashift:DI (match_dup 3) (match_dup 2)))]
> >  {
> >    operands[2] = GEN_INT (ctz_hwi (INTVAL (operands[2])));
> >  })
> > diff --git a/gcc/testsuite/gcc.c-torture/execute/pr91635.c b/gcc/testsuite/gcc.c-torture/execute/pr91635.c
> > new file mode 100644
> > index 00000000000..878a491fc36
> > --- /dev/null
> > +++ b/gcc/testsuite/gcc.c-torture/execute/pr91635.c
> > @@ -0,0 +1,57 @@
> > +/* PR target/91635 */
> > +
> > +#if __CHAR_BIT__ == 8 && __SIZEOF_SHORT__ == 2 \
> > +    && __SIZEOF_INT__ == 4 && __SIZEOF_LONG_LONG__ == 8
> > +unsigned short b, c;
> > +int u, v, w, x;
> > +
> > +__attribute__ ((noipa)) int
> > +foo (unsigned short c)
> > +{
> > +  c <<= __builtin_add_overflow (-c, -1, &b);
> > +  c >>= 1;
> > +  return c;
> > +}
> > +
> > +__attribute__ ((noipa)) int
> > +bar (unsigned short b)
> > +{
> > +  b <<= -14 & 15;
> > +  b = b >> -~1;
> > +  return b;
> > +}
> > +
> > +__attribute__ ((noipa)) int
> > +baz (unsigned short e)
> > +{
> > +  e <<= 1;
> > +  e >>= __builtin_add_overflow (8719476735, u, &v);
> > +  return e;
> > +}
> > +
> > +__attribute__ ((noipa)) int
> > +qux (unsigned int e)
> > +{
> > +  c = ~1;
> > +  c *= e;
> > +  c = c >> (-15 & 5);
> > +  return c + w + x;
> > +}
> > +#endif
> > +
> > +int
> > +main ()
> > +{
> > +#if __CHAR_BIT__ == 8 && __SIZEOF_SHORT__ == 2 \
> > +    && __SIZEOF_INT__ == 4 && __SIZEOF_LONG_LONG__ == 8
> > +  if (foo (0xffff) != 0x7fff)
> > +    __builtin_abort ();
> > +  if (bar (5) != 5)
> > +    __builtin_abort ();
> > +  if (baz (~0) != 0x7fff)
> > +    __builtin_abort ();
> > +  if (qux (2) != 0x7ffe)
> > +    __builtin_abort ();
> > +#endif
> > +  return 0;
> > +}
> > diff --git a/gcc/testsuite/gcc.target/riscv/shift-shift-4.c b/gcc/testsuite/gcc.target/riscv/shift-shift-4.c
> > new file mode 100644
> > index 00000000000..72a45ee87ae
> > --- /dev/null
> > +++ b/gcc/testsuite/gcc.target/riscv/shift-shift-4.c
> > @@ -0,0 +1,13 @@
> > +/* { dg-do compile } */
> > +/* { dg-options "-march=rv32i -mabi=ilp32 -O2" } */
> > +
> > +/* One zero-extend shift can be eliminated by modifying the constant in the
> > +   greater than test.  Started working after modifying the splitter
> > +   lshrsi3_zero_extend_3+1 to use a temporary reg for the first split dest.  */
> > +int
> > +sub (int i)
> > +{
> > +  i &= 0x7fffffff;
> > +  return i > 0x7f800000;
> > +}
> > +/* { dg-final { scan-assembler-not "srli" } } */
> > diff --git a/gcc/testsuite/gcc.target/riscv/shift-shift-5.c b/gcc/testsuite/gcc.target/riscv/shift-shift-5.c
> > new file mode 100644
> > index 00000000000..5b2ae89a471
> > --- /dev/null
> > +++ b/gcc/testsuite/gcc.target/riscv/shift-shift-5.c
> > @@ -0,0 +1,16 @@
> > +/* { dg-do compile } */
> > +/* { dg-options "-march=rv64gc -mabi=lp64d -O2" } */
> > +
> > +/* Fails if lshrsi3_zero_extend_3+1 uses a temp reg which has no REG_DEST
> > +   note.  */
> > +unsigned long
> > +sub (long l)
> > +{
> > +  union u {
> > +    struct s { int a : 19; unsigned int b : 13; int x; } s;
> > +    long l;
> > +  } u;
> > +  u.l = l;
> > +  return u.s.b;
> > +}
> > +/* { dg-final { scan-assembler "srliw" } } */
> > --
> > 2.17.1
> >
> 

-- 
Richard Biener <rguenther@suse.de>
SUSE Software Solutions Germany GmbH, Maxfeldstrasse 5, 90409 Nuernberg,
Germany; GF: Felix Imendörffer; HRB 247165 (AG München)