Re: [PATCH v3] RISC-V: Implement C[LT]Z_DEFINED_VALUE_AT_ZERO

[Philipp Tomsich <philipp.tomsich@vrull.eu>]

Thank you for catching this one.  I'll provide a fix.

On Fri, 3 Jun 2022 at 16:56, H.J. Lu <hjl.tools@gmail.com> wrote:
>
> On Fri, May 13, 2022 at 1:17 PM Philipp Tomsich
> <philipp.tomsich@vrull.eu> wrote:
> >
> > The Zbb support has introduced ctz and clz to the backend, but some
> > transformations in GCC need to know what the value of c[lt]z at zero
> > is. This affects how the optab is generated and may suppress use of
> > CLZ/CTZ in tree passes.
> >
> > Among other things, this is needed for the transformation of
> > table-based ctz-implementations, such as in deepsjeng, to work
> > (see https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90838).
> >
> > Prior to this change, the test case from PR90838 would compile to
> > on RISC-V targets with Zbb:
> >   myctz:
> >         lui     a4,%hi(.LC0)
> >         ld      a4,%lo(.LC0)(a4)
> >         neg     a5,a0
> >         and     a5,a5,a0
> >         mul     a5,a5,a4
> >         lui     a4,%hi(.LANCHOR0)
> >         addi    a4,a4,%lo(.LANCHOR0)
> >         srli    a5,a5,58
> >         sh2add  a5,a5,a4
> >         lw      a0,0(a5)
> >         ret
> >
> > After this change, we get:
> >   myctz:
> >         ctz     a0,a0
> >         andi    a0,a0,63
> >         ret
> >
> > Testing this with deepsjeng_r (from SPEC 2017) against QEMU, this
> > shows a clear reduction in dynamic instruction count:
> >  - before  1961888067076
> >  - after   1907928279874 (2.75% reduction)
> >
> > This also merges the various target-specific test-cases (for x86-64,
> > aarch64 and riscv) within gcc.dg/pr90838.c.
> >
> > This extends the macros (i.e., effective-target keywords) used in
> > testing (lib/target-supports.exp) to reliably distinguish between RV32
> > and RV64 via __riscv_xlen (i.e., the integer register bitwidth) :
> > testing for ILP32 could be misleading (as ILP32 is a valid memory
> > model for 64bit systems).
> >
> > gcc/ChangeLog:
> >
> >         * config/riscv/riscv.h (CLZ_DEFINED_VALUE_AT_ZERO): Implement.
> >         (CTZ_DEFINED_VALUE_AT_ZERO): Same.
> >         * doc/sourcebuild.texi: add documentation for RISC-V specific
> >         test target keywords
> >
> > gcc/testsuite/ChangeLog:
> >
> >         * gcc.dg/pr90838.c: Add additional flags (dg-additional-options)
> >           when compiling for riscv64 and subsume gcc.target/aarch64/pr90838.c
> >           and gcc.target/i386/pr95863-2.c.
> >         * gcc.target/riscv/zbb-ctz.c: New test.
> >         * gcc.target/aarch64/pr90838.c: Removed.
> >         * gcc.target/i386/pr95863-2.c: Removed.
> >         * lib/target-supports.exp: Recognize RV32 or RV64 via XLEN
> >
> > Signed-off-by: Philipp Tomsich <philipp.tomsich@vrull.eu>
> > Signed-off-by: Manolis Tsamis <manolis.tsamis@vrull.eu>
> > Co-developed-by: Manolis Tsamis <manolis.tsamis@vrull.eu>
> >
> > ---
> > Changes in v3:
> > - Address nit from Kito (use rv64 and rv32 on gcc.dg/pr90838.c
> >   consistently.
> >
> > Changes in v2:
> > - Address review comments from Palmer (merging testcases)
> > - Merge the different target-specific testcases for CLZ into one
> > - Add RV32 tests
> > - Fix pr90383.c testcase for x86_64
> >
> >  gcc/config/riscv/riscv.h                   |  5 ++
> >  gcc/doc/sourcebuild.texi                   | 12 ++++
> >  gcc/testsuite/gcc.dg/pr90838.c             | 25 +++++++++
> >  gcc/testsuite/gcc.target/aarch64/pr90838.c | 64 ----------------------
> >  gcc/testsuite/gcc.target/i386/pr95863-2.c  | 27 ---------
> >  gcc/testsuite/lib/target-supports.exp      | 30 ++++++++++
> >  6 files changed, 72 insertions(+), 91 deletions(-)
> >  delete mode 100644 gcc/testsuite/gcc.target/aarch64/pr90838.c
> >  delete mode 100644 gcc/testsuite/gcc.target/i386/pr95863-2.c
> >
> > diff --git a/gcc/config/riscv/riscv.h b/gcc/config/riscv/riscv.h
> > index 8a4d2cf7f85..b191606edb4 100644
> > --- a/gcc/config/riscv/riscv.h
> > +++ b/gcc/config/riscv/riscv.h
> > @@ -1004,4 +1004,9 @@ extern void riscv_remove_unneeded_save_restore_calls (void);
> >
> >  #define HARD_REGNO_RENAME_OK(FROM, TO) riscv_hard_regno_rename_ok (FROM, TO)
> >
> > +#define CLZ_DEFINED_VALUE_AT_ZERO(MODE, VALUE) \
> > +  ((VALUE) = GET_MODE_UNIT_BITSIZE (MODE), 2)
> > +#define CTZ_DEFINED_VALUE_AT_ZERO(MODE, VALUE) \
> > +  ((VALUE) = GET_MODE_UNIT_BITSIZE (MODE), 2)
> > +
> >  #endif /* ! GCC_RISCV_H */
> > diff --git a/gcc/doc/sourcebuild.texi b/gcc/doc/sourcebuild.texi
> > index 613ac29967b..71c04841df2 100644
> > --- a/gcc/doc/sourcebuild.texi
> > +++ b/gcc/doc/sourcebuild.texi
> > @@ -2420,6 +2420,18 @@ PowerPC target pre-defines macro _ARCH_PWR9 which means the @code{-mcpu}
> >  setting is Power9 or later.
> >  @end table
> >
> > +@subsection RISC-V specific attributes
> > +
> > +@table @code
> > +
> > +@item rv32
> > +Test system has an integer register width of 32 bits.
> > +
> > +@item rv64
> > +Test system has an integer register width of 64 bits.
> > +
> > +@end table
> > +
> >  @subsubsection Other hardware attributes
> >
> >  @c Please keep this table sorted alphabetically.
> > diff --git a/gcc/testsuite/gcc.dg/pr90838.c b/gcc/testsuite/gcc.dg/pr90838.c
> > index 41c5dab9a5c..7502b846346 100644
> > --- a/gcc/testsuite/gcc.dg/pr90838.c
> > +++ b/gcc/testsuite/gcc.dg/pr90838.c
> > @@ -1,5 +1,8 @@
> >  /* { dg-do compile } */
> >  /* { dg-options "-O2 -fdump-tree-forwprop2-details" } */
> > +/* { dg-additional-options "-mbmi" { target { { i?86-*-* x86_64-*-* } && { ! { ia32 } } } } } */
> > +/* { dg-additional-options "-march=rv64gc_zbb" { target { rv64 } } } */
> > +/* { dg-additional-options "-march=rv32gc_zbb" { target { rv32 } } } */
> >
> >  int ctz1 (unsigned x)
> >  {
> > @@ -56,4 +59,26 @@ int ctz4 (unsigned long x)
> >    return table[(lsb * magic) >> 58];
> >  }
> >
> > +/* { dg-final { scan-tree-dump-times {= \.CTZ} 4 "forwprop2" { target { { i?86-*-* x86_64-*-* } && { ! { ia32 } } } } } } */
> > +/* { dg-final { scan-assembler-times "tzcntq\t" 1 { target { { i?86-*-* x86_64-*-* } && { ! { ia32 } } } } } } */
> > +/* { dg-final { scan-assembler-times "tzcntl\t" 3 { target { { i?86-*-* x86_64-*-* } && { ! { ia32 } } } } } } */
> > +/* { dg-final { scan-assembler-times "andl\t" 2 { target { { i?86-*-* x86_64-*-* } && { ! { ia32 } } } } } } */
> > +/* { dg-final { scan-assembler-not "negq" { target { { i?86-*-* x86_64-*-* } && { ! { ia32 } } } } } } */
> > +/* { dg-final { scan-assembler-not "imulq" { target { { i?86-*-* x86_64-*-* } && { ! { ia32 } } } } } } */
> > +/* { dg-final { scan-assembler-not "shrq" { target { { i?86-*-* x86_64-*-* } && { ! { ia32 } } } } } } */
> > +
> >  /* { dg-final { scan-tree-dump-times {= \.CTZ} 4 "forwprop2" { target aarch64*-*-* } } } */
> > +/* { dg-final { scan-assembler-times "clz\t" 4 { target aarch64*-*-* } } } */
> > +/* { dg-final { scan-assembler-times "and\t" 2 { target aarch64*-*-* } } } */
> > +/* { dg-final { scan-assembler-not "cmp\t.*0" { target aarch64*-*-* } } } */
> > +
> > +/* { dg-final { scan-tree-dump-times {= \.CTZ} 4 "forwprop2" { target { rv64 } } } } */
> > +/* { dg-final { scan-assembler-times "ctz\t"  1 { target { rv64 } } } } */
> > +/* { dg-final { scan-assembler-times "ctzw\t" 3 { target { rv64 } } } } */
> > +/* { dg-final { scan-assembler-times "andi\t" 2 { target { rv64 } } } } */
> > +/* { dg-final { scan-assembler-not "mul" { target { rv64 } } } } */
> > +
> > +/* { dg-final { scan-tree-dump-times {= \.CTZ} 3 "forwprop2" { target { rv32 } } } } */
> > +/* { dg-final { scan-assembler-times "ctz\t" 3 { target { rv32 } } } } */
> > +/* { dg-final { scan-assembler-times "andi\t" 1 { target { rv32 } } } } */
> > +/* { dg-final { scan-assembler-times "mul\t" 1 { target { rv32 } } } } */
> > diff --git a/gcc/testsuite/gcc.target/aarch64/pr90838.c b/gcc/testsuite/gcc.target/aarch64/pr90838.c
> > deleted file mode 100644
> > index e1e19ac6a61..00000000000
> > --- a/gcc/testsuite/gcc.target/aarch64/pr90838.c
> > +++ /dev/null
> > @@ -1,64 +0,0 @@
> > -/* { dg-do compile } */
> > -/* { dg-options "-O2" } */
> > -
> > -int ctz1 (unsigned x)
> > -{
> > -  static const char table[32] =
> > -    {
> > -      0, 1, 28, 2, 29, 14, 24, 3, 30, 22, 20, 15, 25, 17, 4, 8,
> > -      31, 27, 13, 23, 21, 19, 16, 7, 26, 12, 18, 6, 11, 5, 10, 9
> > -    };
> > -
> > -  return table[((unsigned)((x & -x) * 0x077CB531U)) >> 27];
> > -}
> > -
> > -int ctz2 (unsigned x)
> > -{
> > -#define u 0
> > -  static short table[64] =
> > -    {
> > -      32, 0, 1,12, 2, 6, u,13, 3, u, 7, u, u, u, u,14,
> > -      10, 4, u, u, 8, u, u,25, u, u, u, u, u,21,27,15,
> > -      31,11, 5, u, u, u, u, u, 9, u, u,24, u, u,20,26,
> > -      30, u, u, u, u,23, u,19,29, u,22,18,28,17,16, u
> > -    };
> > -
> > -  x = (x & -x) * 0x0450FBAF;
> > -  return table[x >> 26];
> > -}
> > -
> > -int ctz3 (unsigned x)
> > -{
> > -  static int table[32] =
> > -    {
> > -      0, 1, 2,24, 3,19, 6,25, 22, 4,20,10,16, 7,12,26,
> > -      31,23,18, 5,21, 9,15,11,30,17, 8,14,29,13,28,27
> > -    };
> > -
> > -  if (x == 0) return 32;
> > -  x = (x & -x) * 0x04D7651F;
> > -  return table[x >> 27];
> > -}
> > -
> > -static const unsigned long long magic = 0x03f08c5392f756cdULL;
> > -
> > -static const char table[64] = {
> > -     0,  1, 12,  2, 13, 22, 17,  3,
> > -    14, 33, 23, 36, 18, 58, 28,  4,
> > -    62, 15, 34, 26, 24, 48, 50, 37,
> > -    19, 55, 59, 52, 29, 44, 39,  5,
> > -    63, 11, 21, 16, 32, 35, 57, 27,
> > -    61, 25, 47, 49, 54, 51, 43, 38,
> > -    10, 20, 31, 56, 60, 46, 53, 42,
> > -     9, 30, 45, 41,  8, 40,  7,  6,
> > -};
> > -
> > -int ctz4 (unsigned long x)
> > -{
> > -  unsigned long lsb = x & -x;
> > -  return table[(lsb * magic) >> 58];
> > -}
> > -
> > -/* { dg-final { scan-assembler-times "clz\t" 4 } } */
> > -/* { dg-final { scan-assembler-times "and\t" 2 } } */
> > -/* { dg-final { scan-assembler-not "cmp\t.*0" } } */
> > diff --git a/gcc/testsuite/gcc.target/i386/pr95863-2.c b/gcc/testsuite/gcc.target/i386/pr95863-2.c
> > deleted file mode 100644
> > index cb56dfc6d94..00000000000
> > --- a/gcc/testsuite/gcc.target/i386/pr95863-2.c
> > +++ /dev/null
> > @@ -1,27 +0,0 @@
> > -/* { dg-do compile { target { ! ia32 } } } */
> > -/* { dg-options "-O -mbmi" } */
> > -
> > -static const unsigned long long magic = 0x03f08c5392f756cdULL;
> > -
> > -static const char table[64] = {
> > -     0,  1, 12,  2, 13, 22, 17,  3,
> > -    14, 33, 23, 36, 18, 58, 28,  4,
> > -    62, 15, 34, 26, 24, 48, 50, 37,
> > -    19, 55, 59, 52, 29, 44, 39,  5,
> > -    63, 11, 21, 16, 32, 35, 57, 27,
> > -    61, 25, 47, 49, 54, 51, 43, 38,
> > -    10, 20, 31, 56, 60, 46, 53, 42,
> > -     9, 30, 45, 41,  8, 40,  7,  6,
> > -};
> > -
> > -int ctz4 (unsigned long long x)
>
> This uses long long.  But gcc.dg/pr90838.c has long.  They aren't the same.
> long isn't always 64 bits.  Can you fix it?
>
> Thanks.
>
> > -{
> > -  unsigned long long lsb = x & -x;
> > -  return table[(lsb * magic) >> 58];
> > -}
> > -
> > -/* { dg-final { scan-assembler-times "tzcntq\t" 1 } } */
> > -/* { dg-final { scan-assembler-times "andl\t" 1 } } */
> > -/* { dg-final { scan-assembler-not "negq" } } */
> > -/* { dg-final { scan-assembler-not "imulq" } } */
> > -/* { dg-final { scan-assembler-not "shrq" } } */
> > diff --git a/gcc/testsuite/lib/target-supports.exp b/gcc/testsuite/lib/target-supports.exp
> > index 2d5d0539bb4..244fe2306f4 100644
> > --- a/gcc/testsuite/lib/target-supports.exp
> > +++ b/gcc/testsuite/lib/target-supports.exp
> > @@ -1689,6 +1689,36 @@ proc check_linker_plugin_available { } {
> >    } "-flto -fuse-linker-plugin"]
> >  }
> >
> > +# Return 1 if the target is RV32, 0 otherwise.  Cache the result.
> > +
> > +proc check_effective_target_rv32 { } {
> > +    # Check that we are compiling for RV32 by checking the xlen size.
> > +    return [check_no_compiler_messages riscv_rv32 assembly {
> > +       #if !defined(__riscv_xlen)
> > +       #error "__riscv_xlen not defined!"
> > +       #else
> > +       #if __riscv_xlen != 32
> > +       #error "Not RV32"
> > +       #endif
> > +       #endif
> > +    }]
> > +}
> > +
> > +# Return 1 if the target is RV64, 0 otherwise.  Cache the result.
> > +
> > +proc check_effective_target_rv64 { } {
> > +    # Check that we are compiling for RV64 by checking the xlen size.
> > +    return [check_no_compiler_messages riscv_rv64 assembly {
> > +       #if !defined(__riscv_xlen)
> > +       #error "__riscv_xlen not defined!"
> > +       #else
> > +       #if __riscv_xlen != 64
> > +       #error "Not RV64"
> > +       #endif
> > +       #endif
> > +    }]
> > +}
> > +
> >  # Return 1 if the target OS supports running SSE executables, 0
> >  # otherwise.  Cache the result.
> >
> > --
> > 2.34.1
> >
>
>
> --
> H.J.