On Wed, Sep 10, 2025 at 10:06:35AM +0200, Juergen Christ wrote:
> To properly implement __builtin_ffs for SI mode, implement clz and
> (for >= z17) ctz for SI mode. Otherwise, gcc falls back to a libcall
> which causes problems for Linux kernel code.
>
> Also adjust the C?Z_DEFINED_VALUE_AT_ZERO macros to return 2. Since
> the optabs now return exactly the value set by these macros, return
> value 2 is more appropriate and leads to better code.
>
> Bootstrapped and regtested on s390. Ok for trunk?
>
> gcc/ChangeLog:
>
> * config/s390/s390.h (CLZ_DEFINED_VALUE_AT_ZERO): Adjust and
> return 2.
> (CTZ_DEFINED_VALUE_AT_ZERO): Return 2.
> * config/s390/s390.md (clzsi2): Implement.
> (ctzsi2): Implement.
>
> gcc/testsuite/ChangeLog:
>
> * gcc.dg/vect/pr109011-2.c: Fix expected outcome.
> * gcc.dg/vect/pr109011-4.c: Fix expected outcome.
> * gcc.target/s390/ffs-1.c: New test.
>
> Signed-off-by: Juergen Christ <jchr...@linux.ibm.com>
> ---
> gcc/config/s390/s390.h | 4 ++--
> gcc/config/s390/s390.md | 23 +++++++++++++++++++++++
> gcc/testsuite/gcc.dg/vect/pr109011-2.c | 3 +--
> gcc/testsuite/gcc.dg/vect/pr109011-4.c | 3 +--
> gcc/testsuite/gcc.target/s390/ffs-1.c | 18 ++++++++++++++++++
> 5 files changed, 45 insertions(+), 6 deletions(-)
> create mode 100644 gcc/testsuite/gcc.target/s390/ffs-1.c
>
> diff --git a/gcc/config/s390/s390.h b/gcc/config/s390/s390.h
> index 8b04bc9a7557..6478be8c7acd 100644
> --- a/gcc/config/s390/s390.h
> +++ b/gcc/config/s390/s390.h
> @@ -1001,10 +1001,10 @@ do {
> \
> #define FUNCTION_MODE QImode
>
> /* Specify the value which is used when clz operand is zero. */
> -#define CLZ_DEFINED_VALUE_AT_ZERO(MODE, VALUE) ((VALUE) = 64, 1)
> +#define CLZ_DEFINED_VALUE_AT_ZERO(MODE, VALUE) ((VALUE) = GET_MODE_PRECISION
> (MODE), 2)
>
> /* Specify the value which is used when ctz operand is zero. */
> -#define CTZ_DEFINED_VALUE_AT_ZERO(MODE, VALUE) ((VALUE) = 64, 1)
> +#define CTZ_DEFINED_VALUE_AT_ZERO(MODE, VALUE) ((VALUE) = 64, 2)
>
> /* Machine-specific symbol_ref flags. */
> #define SYMBOL_FLAG_ALIGN_SHIFT SYMBOL_FLAG_MACH_DEP_SHIFT
> diff --git a/gcc/config/s390/s390.md b/gcc/config/s390/s390.md
> index 858387cd85c5..7525688c5fb1 100644
> --- a/gcc/config/s390/s390.md
> +++ b/gcc/config/s390/s390.md
> @@ -9738,6 +9738,19 @@
> "flogr\t%0,%1"
> [(set_attr "op_type" "RRE")])
>
> +(define_expand "clzsi2"
> + [(match_operand:SI 0 "register_operand" "")
> + (match_operand:SI 1 "register_operand" "")]
> + "TARGET_EXTIMM && TARGET_ZARCH"
> +{
> + rtx extreg = gen_reg_rtx (DImode);
> + rtx clzreg = gen_reg_rtx (DImode);
> + emit_insn (gen_zero_extendsidi2 (extreg, operands[1]));
> + emit_insn (gen_clzdi2 (clzreg, extreg));
> + rtx truncreg = gen_lowpart (SImode, clzreg);
> + emit_insn (gen_addsi3 (operands[0], truncreg, GEN_INT(-32)));
^
~~~~
nit: whitespace
Ok otherwise.
Thanks,
Stefan
> + DONE;
> +})
>
> ;;
> ;; Count Trailing Zeros.
> @@ -9750,6 +9763,16 @@
> "ctzg\t%0,%1"
> [(set_attr "op_type" "RRE")])
>
> +(define_expand "ctzsi2"
> + [(set (match_dup 2)
> + (zero_extend:DI (match_operand:SI 1 "register_operand" "")))
> + (set (match_dup 3) (ctz:DI (match_dup 2)))
> + (set (match_operand:SI 0 "register_operand" "") (subreg:SI (match_dup 3)
> 4))]
> + "TARGET_Z17 && TARGET_64BIT"
> +{
> + operands[2] = gen_reg_rtx (DImode);
> + operands[3] = gen_reg_rtx (DImode);
> +})
>
> ;;
> ;;- Rotate instructions.
> diff --git a/gcc/testsuite/gcc.dg/vect/pr109011-2.c
> b/gcc/testsuite/gcc.dg/vect/pr109011-2.c
> index 4c7e6ad07a46..dc62d01da5d9 100644
> --- a/gcc/testsuite/gcc.dg/vect/pr109011-2.c
> +++ b/gcc/testsuite/gcc.dg/vect/pr109011-2.c
> @@ -31,5 +31,4 @@ baz (int *p, int *q)
>
> /* { dg-final { scan-tree-dump-times " = \.CLZ \\\(vect" 3 "optimized" {
> target { { { { i?86-*-* x86_64-*-* } && avx512cd } && lzcnt } && bmi } } } }
> */
> /* { dg-final { scan-tree-dump-times " = \.CTZ \\\(vect" 3 "optimized" {
> target powerpc_vsx } } } */
> -/* { dg-final { scan-tree-dump-times " = \.CTZ \\\(vect" 2 "optimized" {
> target s390_vx } } } */
> -/* { dg-final { scan-tree-dump-times " = \.POPCOUNT \\\(vect" 1 "optimized"
> { target s390_vx } } } */
> +/* { dg-final { scan-tree-dump-times " = \.CTZ \\\(vect" 3 "optimized" {
> target s390_vx } } } */
> diff --git a/gcc/testsuite/gcc.dg/vect/pr109011-4.c
> b/gcc/testsuite/gcc.dg/vect/pr109011-4.c
> index 38b2ab4d511e..8440ec73080a 100644
> --- a/gcc/testsuite/gcc.dg/vect/pr109011-4.c
> +++ b/gcc/testsuite/gcc.dg/vect/pr109011-4.c
> @@ -31,5 +31,4 @@ baz (long long *p, long long *q)
>
> /* { dg-final { scan-tree-dump-times " = \.CLZ \\\(vect" 3 "optimized" {
> target { { { { i?86-*-* x86_64-*-* } && avx512cd } && lzcnt } && bmi } } } }
> */
> /* { dg-final { scan-tree-dump-times " = \.CTZ \\\(vect" 3 "optimized" {
> target powerpc_vsx } } } */
> -/* { dg-final { scan-tree-dump-times " = \.CTZ \\\(vect" 2 "optimized" {
> target s390_vx } } } */
> -/* { dg-final { scan-tree-dump-times " = \.POPCOUNT \\\(vect" 1 "optimized"
> { target s390_vx } } } */
> +/* { dg-final { scan-tree-dump-times " = \.CTZ \\\(vect" 3 "optimized" {
> target s390_vx } } } */
> diff --git a/gcc/testsuite/gcc.target/s390/ffs-1.c
> b/gcc/testsuite/gcc.target/s390/ffs-1.c
> new file mode 100644
> index 000000000000..79774d29ddac
> --- /dev/null
> +++ b/gcc/testsuite/gcc.target/s390/ffs-1.c
> @@ -0,0 +1,18 @@
> +/* Check that __builtin_ffs does not expand to libcall. This is required by
> + Linux kernel code since libcalls are not present there. */
> +/* { dg-do compile } */
> +/* { dg-options "-march=z10" } */
> +
> +long
> +fool (long x)
> +{
> + return __builtin_ffsl (x);
> +}
> +
> +int
> +foo (int x)
> +{
> + return __builtin_ffs (x);
> +}
> +
> +/* { dg-final { scan-assembler-not "brasl" } } */
> --
> 2.43.7
>
