On Mon, Mar 9, 2026 at 2:09 PM Daniel Henrique Barboza
<[email protected]> wrote:
>
> From: Daniel Barboza <[email protected]>
>
> Identify cases where a zero_one comparison is used to conditional
> constant assignment and turn that into an unconditional PLUS. For the
> code in PR71336:
>
> int test(int a) {
> return a & 1 ? 7 : 3;
> }
>
> We'll turn that into "(a&1) * (7 - 3) + 3", which yields the same
> results but without the conditional, promoving more optimization
> opportunities. In an armv8-a target the original code generates:
>
> tst x0, 1 // 38 [c=8 l=4] *anddi3nr_compare0_zextract
> mov w1, 3 // 41 [c=4 l=4] *movsi_aarch64/3
> mov w0, 7 // 42 [c=4 l=4] *movsi_aarch64/3
> csel w0, w1, w0, eq // 17 [c=4 l=4] *cmovsi_insn/0
> ret // 47 [c=0 l=4] *do_return
>
> With this transformation:
>
> ubfiz w0, w0, 2, 1 // 7 [c=4 l=4] *andim_ashiftsi_bfiz
> add w0, w0, 3 // 13 [c=4 l=4] *addsi3_aarch64/0
> ret // 21 [c=0 l=4] *do_return
>
> Similar gains are noticeable in RISC-V and x86.
>
> For completeness sake we're also adding the variant "zero_one == 0".
>
> Bootstrapped and regression tested in x86 and aarch64.
This is a very bad transform on targets that cannot do (wide) integer
multiplication, like AVR. I would suggest to gate this on types
<= word_mode? optab availability isn't going to work since to workaround
similar issues AVR for example implements some of these but with
explicit libgcc dispatch in the insn patterns.
Richard.
> PR tree-optimization/71336
>
> gcc/ChangeLog:
>
> * match.pd(`zero_one EQ|NE 0 ? CST1:CST2`): New pattern.
>
> gcc/testsuite/ChangeLog:
>
> * gcc.dg/tree-ssa/pr71336-2.c: New test.
> * gcc.dg/tree-ssa/pr71336.c: New test.
> ---
> gcc/match.pd | 36 ++++++++++++++
> gcc/testsuite/gcc.dg/tree-ssa/pr71336-2.c | 59 +++++++++++++++++++++++
> gcc/testsuite/gcc.dg/tree-ssa/pr71336.c | 20 ++++++++
> 3 files changed, 115 insertions(+)
> create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/pr71336-2.c
> create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/pr71336.c
>
> diff --git a/gcc/match.pd b/gcc/match.pd
> index 7f16fd4e081..d041276c595 100644
> --- a/gcc/match.pd
> +++ b/gcc/match.pd
> @@ -5195,6 +5195,42 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
> && expr_no_side_effects_p (@2))
> (op (mult (convert:type @0) @2) @1))))
>
> +/* PR71336:
> + zero_one != 0 ? CST1 : CST2 -> ((typeof (CST2))zero_one * diff) + CST2,
> + where CST1 > CST2 and diff = CST1 - CST2.
> +
> + Includes the "zero_one == 0 ? (...)" variant too. */
> +(for cmp (ne eq)
> + (simplify
> + (cond (cmp zero_one_valued_p@0 integer_zerop) INTEGER_CST@1 INTEGER_CST@2)
> + (with {
> + unsigned HOST_WIDE_INT diff = 0;
> +
> + if (tree_int_cst_sgn (@1) > 0 && tree_int_cst_sgn (@2) > 0
> + && tree_fits_uhwi_p (@1) && tree_fits_uhwi_p (@2))
> + {
> + if (cmp == NE_EXPR
> + && wi::gtu_p (wi::to_wide (@1), wi::to_wide (@2)))
> + diff = tree_to_uhwi (@1) - tree_to_uhwi (@2);
> +
> + if (cmp == EQ_EXPR
> + && wi::gtu_p (wi::to_wide (@2), wi::to_wide (@1)))
> + diff = tree_to_uhwi (@2) - tree_to_uhwi (@1);
> + }
> + }
> + (if (cmp == NE_EXPR
> + && INTEGRAL_TYPE_P (type)
> + && INTEGRAL_TYPE_P (TREE_TYPE (@0))
> + && diff > 0)
> + (plus (mult (convert:type @0) { build_int_cst (type, diff); })
> + @2)
> + (if (cmp == EQ_EXPR
> + && INTEGRAL_TYPE_P (type)
> + && INTEGRAL_TYPE_P (TREE_TYPE (@0))
> + && diff > 0)
> + (plus (mult (convert:type @0) { build_int_cst (type, diff); })
> + @1))))))
> +
> /* ?: Value replacement. */
> /* a == 0 ? b : b + a -> b + a */
> (for op (plus bit_ior bit_xor)
> diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr71336-2.c
> b/gcc/testsuite/gcc.dg/tree-ssa/pr71336-2.c
> new file mode 100644
> index 00000000000..da44489d3e4
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/tree-ssa/pr71336-2.c
> @@ -0,0 +1,59 @@
> +/* { dg-do run } */
> +/* { dg-options "-O1" } */
> +
> +/* Macro adapted from builtin-object-size-common.h */
> +#define FAIL() \
> + do { \
> + __builtin_printf ("Failure at line: %d\n", __LINE__); \
> + abort(); \
> + } while (0)
> +
> +void abort(void);
> +
> +int test (int a) {
> + return a & 1 ? 7 : 3;
> +}
> +
> +int test2 (int a) {
> + return a & 1 ? 3 : 7;
> +}
> +
> +int test3 (int a) {
> + return (a & 1) == 0 ? 3 : 7;
> +}
> +
> +int test4 (int a) {
> + return (a & 1) == 0 ? 7 : 3;
> +}
> +
> +int main (void) {
> + if (test (0) != 3)
> + FAIL ();
> + if (test (1) != 7)
> + FAIL ();
> + if (test (3) != 7)
> + FAIL ();
> +
> + if (test2 (0) != 7)
> + FAIL ();
> + if (test2 (1) != 3)
> + FAIL ();
> + if (test2 (3) != 3)
> + FAIL ();
> +
> + if (test3 (0) != 3)
> + FAIL ();
> + if (test3 (1) != 7)
> + FAIL ();
> + if (test3 (2) != 3)
> + FAIL ();
> +
> + if (test4 (0) != 7)
> + FAIL ();
> + if (test4 (1) != 3)
> + FAIL ();
> + if (test4 (2) != 7)
> + FAIL ();
> +
> + return 0;
> +}
> diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr71336.c
> b/gcc/testsuite/gcc.dg/tree-ssa/pr71336.c
> new file mode 100644
> index 00000000000..fb643bf1eb3
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/tree-ssa/pr71336.c
> @@ -0,0 +1,20 @@
> +/* { dg-additional-options -O1 } */
> +/* { dg-additional-options -fdump-tree-gimple } */
> +
> +int test (int a) {
> + return a & 1 ? 7 : 3;
> +}
> +
> +int test2 (int a) {
> + return (a & 1) == 0 ? 3 : 7;
> +}
> +
> +int test3 (int a) {
> + return a & 1 ? 17 : 3;
> +}
> +
> +int test4 (int a) {
> + return (a & 1) == 0 ? 3 : 17;
> +}
> +
> +/* { dg-final { scan-tree-dump-times " goto " 0 gimple } } */
> --
> 2.43.0
>
