> On 5 Jun 2026, at 12:11, Andrew Pinski <[email protected]> wrote:
>
> This takes https://gcc.gnu.org/pipermail/gcc-patches/2026-June/719384.html
> and merge it into factor_out_conditional_operation. Also expands it to
> allow for more than just unary and binary operands.
> It handles as similar as what ifcvt does in factor_out_operators
> but rejects some cases due to those not being profitable.
> The cases which are not profitable:
> * pointer plus in early with constant operand 1 (except if equal).
> * division/mod with constant operand 1
>
> some cases needed to be rejected for validity (copied from ifcvt):
> * BIT_FIELD_REF/BIT_INSERT_EXPR (non first operand)
> * VEC_PERM_EXPR with constant operand 2
>
> Notes on the testcase changes:
> The recip-*.c testcases need to be disable phiopt since it removes
> a division in some cases which causes the recip pass not to run.
>
> slsr-12.c and slsr-34.c need to be xfailed. SLSR pass is mostly
> in maintaince mode and is not getting improved.
>
> pr122629-1.c and vect-reduc-cond-2.c are now handled in phiopt
> rather than ifcvt.
>
> PR tree-optimization/125557
> PR tree-optimization/64700
> PR tree-optimization/29144
> PR tree-optimization/94274
> gcc/ChangeLog:
>
> * tree-if-conv.cc: Include tree-ssa-phiopt.h
> (find_different_opnum): Move to ...
> * tree-ssa-phiopt.cc (find_different_opnum): Here.
> (is_divide_or_mod_p): New function.
> (factor_out_conditional_operation): Handle operands > 1,
> including operands communitive operands. Add early_p argument
> for costing.
> (pass_phiopt::execute): Pass early_p to
> factor_out_conditional_operation.
> * tree-ssa-phiopt.h: New file.
>
> gcc/testsuite/ChangeLog:
>
> * gcc.dg/tree-ssa/recip-3.c: Disable phiopt since it removes
> one division and recip pass needs 3.
> * gcc.dg/tree-ssa/recip-5.c: Likewise.
> * gcc.dg/tree-ssa/recip-6.c: Likewise.
> * gcc.dg/tree-ssa/recip-7.c: Likewise.
> * gcc.dg/tree-ssa/slsr-12.c: xfail.
> * gcc.dg/tree-ssa/slsr-34.c: Likewise.
> * gcc.dg/tree-ssa/pr122629-1.c: Update to scan phiopt1.
> * gcc.dg/vect/vect-reduc-cond-2.c: Likewise.
> * gcc.dg/tree-ssa/phi-factor-binary-1.c: New test.
> * gcc.dg/tree-ssa/phi-factor-binary-2.c: New test.
> * gcc.target/aarch64/phi-factor-binary-1.c: New test.
> Co-authored-by: Kyrylo Tkachov <[email protected]>
>
> Signed-off-by: Andrew Pinski <[email protected]>
> ---
> .../gcc.dg/tree-ssa/phi-factor-binary-1.c | 20 ++
> .../gcc.dg/tree-ssa/phi-factor-binary-2.c | 41 +++++
> gcc/testsuite/gcc.dg/tree-ssa/pr122629-1.c | 4 +-
> gcc/testsuite/gcc.dg/tree-ssa/recip-3.c | 3 +
> gcc/testsuite/gcc.dg/tree-ssa/recip-5.c | 2 +-
> gcc/testsuite/gcc.dg/tree-ssa/recip-6.c | 2 +-
> gcc/testsuite/gcc.dg/tree-ssa/recip-7.c | 2 +-
> gcc/testsuite/gcc.dg/tree-ssa/slsr-12.c | 2 +-
> gcc/testsuite/gcc.dg/tree-ssa/slsr-34.c | 2 +-
> gcc/testsuite/gcc.dg/vect/vect-reduc-cond-2.c | 4 +-
> .../gcc.target/aarch64/phi-factor-binary-1.c | 60 ++++++
> gcc/tree-if-conv.cc | 80 +-------
> gcc/tree-ssa-phiopt.cc | 172 ++++++++++++++++--
> gcc/tree-ssa-phiopt.h | 24 +++
> 14 files changed, 319 insertions(+), 99 deletions(-)
> create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/phi-factor-binary-1.c
> create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/phi-factor-binary-2.c
> create mode 100644 gcc/testsuite/gcc.target/aarch64/phi-factor-binary-1.c
> create mode 100644 gcc/tree-ssa-phiopt.h
>
> diff --git a/gcc/testsuite/gcc.dg/tree-ssa/phi-factor-binary-1.c
> b/gcc/testsuite/gcc.dg/tree-ssa/phi-factor-binary-1.c
> new file mode 100644
> index 00000000000..bfcae888125
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/tree-ssa/phi-factor-binary-1.c
> @@ -0,0 +1,20 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O2 -fdump-tree-phiopt1-details" } */
> +
> +/* PR tree-optimization/125557. Both arms of the diamond apply the same
> binary
> + operation sharing one operand (* c), so phi-opt factors it out: the join
> + becomes t = PHI <a, b>; x = t * c -- one multiply at the merge instead of
> + one in each arm, and no extra PHI. */
> +
> +int
> +f (int cond, int a, int b, int c)
> +{
> + int x;
> + if (cond)
> + x = a * c;
> + else
> + x = b * c;
> + return x;
> +}
> +
> +/* { dg-final { scan-tree-dump " changed to factor operation out from
> COND_EXP" "phiopt1" } } */
> diff --git a/gcc/testsuite/gcc.dg/tree-ssa/phi-factor-binary-2.c
> b/gcc/testsuite/gcc.dg/tree-ssa/phi-factor-binary-2.c
> new file mode 100644
> index 00000000000..eb7669b664b
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/tree-ssa/phi-factor-binary-2.c
> @@ -0,0 +1,41 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O2 -fdump-tree-phiopt1-details" } */
> +
> +/* tree-optimization/125557. factor_out_binary_common_operand handles more
> than
> + one operation kind and, when several join PHIs share the differing
> operand,
> + factors each of them -- collapsing the arms to a single select. */
> +
> +/* Two PHIs share the differing operand a/b: the multiply and the add are
> each
> + factored out, so both arms reduce to one select of a/b. */
> +void
> +f2 (int cond, int a, int b, int c, int d, int *p, int *q)
> +{
> + int x, y;
> + if (cond)
> + {
> + x = a * c;
> + y = a + d;
> + }
> + else
> + {
> + x = b * c;
> + y = b + d;
> + }
> + *p = x;
> + *q = y;
> +}
> +
> +/* A shift is factored just like the arithmetic ops. */
> +unsigned long
> +f3 (int cond, unsigned long a, unsigned long b, int s)
> +{
> + unsigned long x;
> + if (cond)
> + x = a << s;
> + else
> + x = b << s;
> + return x;
> +}
> +
> +/* f2 factors twice (the * and the +), f3 once (the <<). */
> +/* { dg-final { scan-tree-dump-times " changed to factor operation out from
> COND_EXP" 3 "phiopt1" } } */
> diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr122629-1.c
> b/gcc/testsuite/gcc.dg/tree-ssa/pr122629-1.c
> index a80d4a1990b..54f7bf11d48 100644
> --- a/gcc/testsuite/gcc.dg/tree-ssa/pr122629-1.c
> +++ b/gcc/testsuite/gcc.dg/tree-ssa/pr122629-1.c
> @@ -1,5 +1,5 @@
> /* { dg-do compile } */
> -/* { dg-options "-O2 -fdump-tree-ifcvt-details" } */
> +/* { dg-options "-O2 -fdump-tree-ifcvt-details -fdump-tree-phiopt-details" }
> */
> /* PR tree-optimization/122629 */
>
> typedef int ix4 __attribute__((vector_size(4*sizeof(int))));
> @@ -33,4 +33,4 @@ int g(ix4 *a, int l, int *b, ix4 *c)
> }
>
> /* Make sure BIT_INSERT_EXPR/BIT_FIELD_REF is still factored out for the case
> if operand 0 is different. */
> -/* { dg-final { scan-tree-dump-times "changed to factor operation out from"
> 2 "ifcvt" } } */
> +/* { dg-final { scan-tree-dump-times "changed to factor operation out from"
> 2 "phiopt1" } } */
> diff --git a/gcc/testsuite/gcc.dg/tree-ssa/recip-3.c
> b/gcc/testsuite/gcc.dg/tree-ssa/recip-3.c
> index 036f32a9c33..3c6df8d0726 100644
> --- a/gcc/testsuite/gcc.dg/tree-ssa/recip-3.c
> +++ b/gcc/testsuite/gcc.dg/tree-ssa/recip-3.c
> @@ -5,6 +5,9 @@
> to optimize a sequence. With a FP enabled ranger, we eliminate one of them
> earlier, causing the pass to skip this optimization. */
> /* { dg-additional-options "-fno-thread-jumps -fno-tree-dominator-opts" } */
> +/* PHI-OPT will factor out the `/d` from the `?:` expression which means
> there will
> + only be 2 `/d` left so disable that. */
> +/* { dg-additional-options "-fno-ssa-phiopt" } */
>
> double F[5] = { 0.0, 0.0 }, e;
>
> diff --git a/gcc/testsuite/gcc.dg/tree-ssa/recip-5.c
> b/gcc/testsuite/gcc.dg/tree-ssa/recip-5.c
> index 6ac0559bc7c..f05cfe866cc 100644
> --- a/gcc/testsuite/gcc.dg/tree-ssa/recip-5.c
> +++ b/gcc/testsuite/gcc.dg/tree-ssa/recip-5.c
> @@ -1,4 +1,4 @@
> -/* { dg-options "-O1 -funsafe-math-optimizations -ftrapping-math
> -fdump-tree-recip -fdump-tree-optimized" } */
> +/* { dg-options "-O1 -funsafe-math-optimizations -ftrapping-math
> -fdump-tree-recip -fdump-tree-optimized -fno-ssa-phiopt" } */
> /* { dg-do compile } */
> /* { dg-warning "'-fassociative-math' disabled" "" { target *-*-* } 0 } */
>
> diff --git a/gcc/testsuite/gcc.dg/tree-ssa/recip-6.c
> b/gcc/testsuite/gcc.dg/tree-ssa/recip-6.c
> index b5d537a6ccd..c172fb34fcf 100644
> --- a/gcc/testsuite/gcc.dg/tree-ssa/recip-6.c
> +++ b/gcc/testsuite/gcc.dg/tree-ssa/recip-6.c
> @@ -1,4 +1,4 @@
> -/* { dg-options "-O1 -funsafe-math-optimizations -fno-trapping-math
> -fdump-tree-recip" } */
> +/* { dg-options "-O1 -funsafe-math-optimizations -fno-trapping-math
> -fdump-tree-recip -fno-ssa-phiopt" } */
> /* { dg-do compile } */
>
> /* Test inserting in a block that does not contain a division. */
> diff --git a/gcc/testsuite/gcc.dg/tree-ssa/recip-7.c
> b/gcc/testsuite/gcc.dg/tree-ssa/recip-7.c
> index 13fca0b0e09..0e205d17891 100644
> --- a/gcc/testsuite/gcc.dg/tree-ssa/recip-7.c
> +++ b/gcc/testsuite/gcc.dg/tree-ssa/recip-7.c
> @@ -1,4 +1,4 @@
> -/* { dg-options "-O1 -funsafe-math-optimizations -fno-trapping-math
> -fdump-tree-recip" } */
> +/* { dg-options "-O1 -funsafe-math-optimizations -fno-trapping-math
> -fdump-tree-recip -fno-ssa-phiopt" } */
> /* { dg-do compile } */
>
> /* Test inserting in a block that does not contain a division. */
> diff --git a/gcc/testsuite/gcc.dg/tree-ssa/slsr-12.c
> b/gcc/testsuite/gcc.dg/tree-ssa/slsr-12.c
> index f92b70ffafb..f50c2020157 100644
> --- a/gcc/testsuite/gcc.dg/tree-ssa/slsr-12.c
> +++ b/gcc/testsuite/gcc.dg/tree-ssa/slsr-12.c
> @@ -26,4 +26,4 @@ f (int s, int c)
> return x;
> }
>
> -/* { dg-final { scan-tree-dump-times " \\* " 3 "optimized" } } */
> +/* { dg-final { scan-tree-dump-times " \\* " 3 "optimized" { xfail *-*-* } }
> } */
> diff --git a/gcc/testsuite/gcc.dg/tree-ssa/slsr-34.c
> b/gcc/testsuite/gcc.dg/tree-ssa/slsr-34.c
> index d7ede2efe8c..31d59b84d49 100644
> --- a/gcc/testsuite/gcc.dg/tree-ssa/slsr-34.c
> +++ b/gcc/testsuite/gcc.dg/tree-ssa/slsr-34.c
> @@ -38,5 +38,5 @@ f (int c, int i)
> return x;
> }
>
> -/* { dg-final { scan-tree-dump-times " \\* " 1 "optimized" } } */
> +/* { dg-final { scan-tree-dump-times " \\* " 1 "optimized" { xfail *-*-* } }
> } */
> /* { dg-final { scan-tree-dump-times "PHI" 2 "optimized" } } */
> diff --git a/gcc/testsuite/gcc.dg/vect/vect-reduc-cond-2.c
> b/gcc/testsuite/gcc.dg/vect/vect-reduc-cond-2.c
> index 126a50f3e56..aa204d1ab67 100644
> --- a/gcc/testsuite/gcc.dg/vect/vect-reduc-cond-2.c
> +++ b/gcc/testsuite/gcc.dg/vect/vect-reduc-cond-2.c
> @@ -1,6 +1,6 @@
> /* { dg-require-effective-target vect_int } */
> /* { dg-require-effective-target vect_condition } */
> -/* { dg-additional-options "-fdump-tree-ifcvt-details" } */
> +/* { dg-additional-options "-fdump-tree-phiopt1-details" } */
>
> #include <stdarg.h>
> #include "tree-vect.h"
> @@ -59,4 +59,4 @@ int main (void)
> }
>
> /* { dg-final { scan-tree-dump-times "vectorized 1 loops" 1 "vect" { xfail {
> vect_no_int_add } } } } */
> -/* { dg-final { scan-tree-dump-times "changed to factor operation out from
> COND_EXPR" 2 "ifcvt" } } */
> +/* { dg-final { scan-tree-dump-times "changed to factor operation out from
> COND_EXPR" 2 "phiopt1" } } */
> diff --git a/gcc/testsuite/gcc.target/aarch64/phi-factor-binary-1.c
> b/gcc/testsuite/gcc.target/aarch64/phi-factor-binary-1.c
> new file mode 100644
> index 00000000000..fd6b4f556c0
> --- /dev/null
> +++ b/gcc/testsuite/gcc.target/aarch64/phi-factor-binary-1.c
> @@ -0,0 +1,60 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O2" } */
> +
> +/* tree-optimization/125557: factor_out_binary_common_operand computes a
> binary
> + operation shared between a PHI's two arms once, behind a single select,
> + instead of once per arm -- and when several join PHIs share the differing
> + operand it collapses them to one select, which also removes the
> + data-dependent branch. These are the asm wins of patch 1 on its own. */
> +
> +/* f1: one multiply behind a select, not one per arm. */
> +int
> +f1 (int cond, int a, int b, int c)
> +{
> + int x;
> + if (cond)
> + x = a * c;
> + else
> + x = b * c;
> + return x;
> +}
> +
> +/* f3: one shift, not one per arm (snappy's address-arithmetic shape). */
> +unsigned long
> +f3 (int cond, unsigned long a, unsigned long b, int s)
> +{
> + unsigned long x;
> + if (cond)
> + x = a << s;
> + else
> + x = b << s;
> + return x;
> +}
> +
> +/* f2: two results share the differing operand (a/b): one select feeds both,
> so
> + only one multiply and one add remain and the diamond is branchless. */
> +void
> +f2 (int cond, int a, int b, int c, int d, int *p, int *q)
> +{
> + int x, y;
> + if (cond)
> + {
> + x = a * c;
> + y = a + d;
> + }
> + else
> + {
> + x = b * c;
> + y = b + d;
> + }
> + *p = x;
> + *q = y;
> +}
> +
> +/* f1 and f2 each keep a single multiply (two without the factoring). */
> +/* { dg-final { scan-assembler-times {\tmul\t} 2 } } */
> +/* f3 keeps a single shift (two without the factoring). */
> +/* { dg-final { scan-assembler-times {\tlsl\t} 1 } } */
> +/* Each diamond becomes a branchless select; no data-dependent branch
> remains. */
> +/* { dg-final { scan-assembler-not {\tcbn?z\t} } } */
> +/* { dg-final { scan-assembler-not {\tb\.[a-z]} } } */
> diff --git a/gcc/tree-if-conv.cc b/gcc/tree-if-conv.cc
> index b685e30bd0b..b8ae52100fb 100644
> --- a/gcc/tree-if-conv.cc
> +++ b/gcc/tree-if-conv.cc
> @@ -124,6 +124,7 @@ along with GCC; see the file COPYING3. If not see
> #include "tree-vectorizer.h"
> #include "tree-eh.h"
> #include "cgraph.h"
> +#include "tree-ssa-phiopt.h"
>
> /* For lang_hooks.types.type_for_mode. */
> #include "langhooks.h"
> @@ -2173,85 +2174,6 @@ gen_phi_arg_condition (gphi *phi, ifcvt_arg_entry_t
> &arg,
> return cond;
> }
>
> -/* Find the operand which is different between ARG0_OP and ARG1_OP.
> - Returns the operand num where the difference is.
> - Set NEWARG0 and NEWARG1 from the different argument.
> - Returns -1 if none is found.
> - If ARG0_OP/ARG1_OP is commutative also try swapping the
> - two commutative operands and return the operand number where
> - the difference happens in ARG0_OP. */
> -
> -static int
> -find_different_opnum (const gimple_match_op &arg0_op,
> - const gimple_match_op &arg1_op,
> - tree *new_arg0, tree *new_arg1)
> -{
> - unsigned opnum = -1;
> - unsigned first;
> - first = first_commutative_argument (arg1_op.code, arg1_op.type);
> - for (unsigned i = 0; i < arg0_op.num_ops; i++)
> - {
> - if (!operand_equal_for_phi_arg_p (arg0_op.ops[i],
> - arg1_op.ops[i]))
> - {
> - /* Can handle only one non equal operand. */
> - if (opnum != -1u)
> - {
> - /* Though if opnum is right before i and opnum is equal
> - to the first communtative argument, handle communtative
> - specially. */
> - if (i == opnum + 1 && opnum == first)
> - goto commutative;
> - return -1;
> - }
> - opnum = i;
> - }
> - }
> - /* If all operands are equal only do this is there was single
> - operand. */
> - if (opnum == -1u)
> - {
> - if (arg0_op.num_ops != 1)
> - return -1;
> - opnum = 0;
> - }
> - *new_arg0 = arg0_op.ops[opnum];
> - *new_arg1 = arg1_op.ops[opnum];
> - return opnum;
> -
> -/* Handle commutative operations. */
> -commutative:
> - gcc_assert (first != -1u);
> -
> - /* Check the rest of the arguments to make sure they are the same. */
> - for (unsigned i = first + 2; i < arg0_op.num_ops; i++)
> - if (!operand_equal_for_phi_arg_p (arg0_op.ops[i],
> - arg1_op.ops[i]))
> - return -1;
> -
> - /* If the arg0[first+1] and arg1[first] are the same
> - then the one which is different is arg0[first] and arg1[first+1]
> - return first since this is based on arg0. */
> - if (operand_equal_for_phi_arg_p (arg0_op.ops[first + 1],
> - arg1_op.ops[first]))
> - {
> - *new_arg0 = arg0_op.ops[first];
> - *new_arg1 = arg1_op.ops[first + 1];
> - return first;
> - }
> - /* If the arg0[first] and arg1[first+1] are the same
> - then the one which is different is arg0[first+1] and arg1[first]
> - return first+1 since this is based on arg0. */
> - if (operand_equal_for_phi_arg_p (arg0_op.ops[first],
> - arg1_op.ops[first + 1]))
> - {
> - *new_arg0 = arg0_op.ops[first + 1];
> - *new_arg1 = arg1_op.ops[first];
> - return first + 1;
> - }
> - return -1;
> -}
> -
> /* Factors out an operation from *ARG0 and *ARG1 and
> create the new statement at GSI. *RES is the
> result of that new statement. Update *ARG0 and *ARG1
> diff --git a/gcc/tree-ssa-phiopt.cc b/gcc/tree-ssa-phiopt.cc
> index 6a7e4c70722..f8881e61d2f 100644
> --- a/gcc/tree-ssa-phiopt.cc
> +++ b/gcc/tree-ssa-phiopt.cc
> @@ -297,6 +297,104 @@ is_factor_profitable (gimple *def_stmt, basic_block
> merge, tree arg)
> return true;
> }
>
> +/* Return true if CODE is an integer division or integer mod code. */
> +static bool
> +is_divide_or_mod_p (const code_helper &code)
> +{
> + switch (code.get_rep())
> + {
> + case TRUNC_DIV_EXPR:
> + case CEIL_DIV_EXPR:
> + case FLOOR_DIV_EXPR:
> + case ROUND_DIV_EXPR:
> + case EXACT_DIV_EXPR:
> + case TRUNC_MOD_EXPR:
> + case FLOOR_MOD_EXPR:
> + return true;
> + default:
> + return false;
> + }
> +}
> +
> +/* Find the operand which is different between ARG0_OP and ARG1_OP.
> + Returns the operand num where the difference is.
> + Set NEWARG0 and NEWARG1 from the different argument.
> + Returns -1 if none is found.
> + If ARG0_OP/ARG1_OP is commutative also try swapping the
> + two commutative operands and return the operand number where
> + the difference happens in ARG0_OP. */
> +
> +int
> +find_different_opnum (const gimple_match_op &arg0_op,
> + const gimple_match_op &arg1_op,
> + tree *new_arg0, tree *new_arg1)
> +{
> + unsigned opnum = -1;
> + unsigned first;
> + first = first_commutative_argument (arg1_op.code, arg1_op.type);
> + for (unsigned i = 0; i < arg0_op.num_ops; i++)
> + {
> + if (!operand_equal_for_phi_arg_p (arg0_op.ops[i],
> + arg1_op.ops[i]))
> + {
> + /* Can handle only one non equal operand. */
> + if (opnum != -1u)
> + {
> + /* Though if opnum is right before i and opnum is equal
> + to the first communtative argument, handle communtative
> + specially. */
> + if (i == opnum + 1 && opnum == first)
> + goto commutative;
> + return -1;
> + }
> + opnum = i;
> + }
> + }
> + /* If all operands are equal only do this is there was single
> + operand. */
> + if (opnum == -1u)
> + {
> + if (arg0_op.num_ops != 1)
> + return -1;
> + opnum = 0;
> + }
> + *new_arg0 = arg0_op.ops[opnum];
> + *new_arg1 = arg1_op.ops[opnum];
> + return opnum;
> +
> +/* Handle commutative operations. */
> +commutative:
> + gcc_assert (first != -1u);
> +
> + /* Check the rest of the arguments to make sure they are the same. */
> + for (unsigned i = first + 2; i < arg0_op.num_ops; i++)
> + if (!operand_equal_for_phi_arg_p (arg0_op.ops[i],
> + arg1_op.ops[i]))
> + return -1;
> +
> + /* If the arg0[first+1] and arg1[first] are the same
> + then the one which is different is arg0[first] and arg1[first+1]
> + return first since this is based on arg0. */
> + if (operand_equal_for_phi_arg_p (arg0_op.ops[first + 1],
> + arg1_op.ops[first]))
> + {
> + *new_arg0 = arg0_op.ops[first];
> + *new_arg1 = arg1_op.ops[first + 1];
> + return first;
> + }
> + /* If the arg0[first] and arg1[first+1] are the same
> + then the one which is different is arg0[first+1] and arg1[first]
> + return first+1 since this is based on arg0. */
> + if (operand_equal_for_phi_arg_p (arg0_op.ops[first],
> + arg1_op.ops[first + 1]))
> + {
> + *new_arg0 = arg0_op.ops[first + 1];
> + *new_arg1 = arg1_op.ops[first];
> + return first + 1;
> + }
> + return -1;
> +}
> +
> /* PR66726: Factor operations out of COND_EXPR. If the arguments of the PHI
> stmt are Unary operator, factor out the operation and perform the operation
> to the result of PHI stmt. COND_STMT is the controlling predicate.
> @@ -304,7 +402,8 @@ is_factor_profitable (gimple *def_stmt, basic_block
> merge, tree arg)
>
> static bool
> factor_out_conditional_operation (edge e0, edge e1, basic_block merge,
> - gphi *phi, gimple *cond_stmt)
> + gphi *phi, gimple *cond_stmt,
> + bool early_p)
> {
> gimple *arg0_def_stmt = NULL, *arg1_def_stmt = NULL;
> tree temp, result;
> @@ -358,19 +457,14 @@ factor_out_conditional_operation (edge e0, edge e1,
> basic_block merge,
> if (arg0_op.operands_occurs_in_abnormal_phi ())
> return false;
>
> - /* Currently just support one operand expressions. */
> - if (arg0_op.num_ops != 1)
> - return false;
> -
> - tree new_arg0 = arg0_op.ops[0];
> + tree new_arg0;
> tree new_arg1;
> + int opnum = -1;
>
> /* If arg0 have > 1 use, then this transformation actually increases
> the number of expressions evaluated at runtime. */
> if (!has_single_use (arg0))
> return false;
> - if (!is_factor_profitable (arg0_def_stmt, merge, new_arg0))
> - return false;
> if (gimple_has_location (arg0_def_stmt))
> narg0_loc = gimple_location (arg0_def_stmt);
>
> @@ -387,12 +481,62 @@ factor_out_conditional_operation (edge e0, edge e1,
> basic_block merge,
> if (arg1_op.operands_occurs_in_abnormal_phi ())
> return false;
>
> + /* For the complex expression, don't factor
> + out, that will confuse the uninitializing
> + warnings. */
> + if (arg1_op.code == COMPLEX_EXPR)
> + return false;
Btw, since you asked about it in your review of my patch, this is needed to
avoid regressing gcc.dg/uninit-17.c
> +
> /* If arg1 have > 1 use, then this transformation actually increases
> the number of expressions evaluated at runtime. */
> if (!has_single_use (arg1))
> return false;
>
> - new_arg1 = arg1_op.ops[0];
> + opnum = find_different_opnum (arg0_op, arg1_op, &new_arg0, &new_arg1);
> + if (opnum == -1)
> + return false;
> + /* If this was a division and the operand is the divisor
> + and either divisor was a constant, don't factor out
> + the division; dividing by an explicit constant can be
> + expanded better than without an constant.
> + FIXME: maybe isel could undo this case. */
> + if (is_divide_or_mod_p (arg1_op.code)
> + && opnum == 1
> + && (poly_int_tree_p (new_arg0)
> + || poly_int_tree_p (new_arg1)))
> + return false;
> +
> + /* For early phiopt, don't factor out constants for pointer plus
> except if they are equal. */
> + if (early_p && arg1_op.code == POINTER_PLUS_EXPR
> + && opnum == 1
> + && TREE_CODE (new_arg0) != SSA_NAME
> + && TREE_CODE (new_arg1) != SSA_NAME
> + && !operand_equal_p (new_arg0, new_arg1))
> + return false;
I think allowing the factoring of constants for other expressions like
PLUS_EXPR leads to regressions in the aarch64 test suite in
gcc.target/aarch64/cinc_common_1.c and gcc.target/aarch64/fuse_cmp_csel.c
I ran into the same thing and ended up replacing the narrow POINTER_PLUS guard
with an unconditional "don't introduce a PHI of two constants” check.
if (TREE_CODE (new_arg0) != SSA_NAME && TREE_CODE (new_arg1) != SSA_NAME)
return false;
This is a strict superset of the early_p POINTER_PLUS guard — the
!operand_equal_p
sub-case there can't actually be reached, since find_different_opnum only
reports an operand as differing when it isn't operand-equal — so the
POINTER_PLUS guard can be dropped. I think that would allow avoiding some slsr
and recip tests fallout. But up to you if you want to keep it.
Thanks,
Kyrill
> +
> + /* BIT_FIELD_REF and BIT_INSERT_EXPR can't be factored out for non-0
> operands
> + as the other operands require constants. */
> + if ((arg1_op.code == BIT_FIELD_REF
> + || arg1_op.code == BIT_INSERT_EXPR)
> + && opnum != 0)
> + return false;
> +
> + /* It is not profitability to factor out vec_perm with
> + constant masks (operand 2). The target might not support it
> + and that might be invalid to do as such. Also with constants
> + masks, the number of elements of the mask type does not need
> + to match the number of elements of other operands and can be
> + arbitrary integral vector type so factoring that out can't work.
> + Note in the case where one mask is a constant and the other is not,
> + the next check for compatible types will reject the case the
> + constant mask has the incompatible type. */
> + if (arg1_op.code == VEC_PERM_EXPR && opnum == 2
> + && TREE_CODE (new_arg0) == VECTOR_CST
> + && TREE_CODE (new_arg1) == VECTOR_CST)
> + return false;
> +
> + if (!is_factor_profitable (arg0_def_stmt, merge, new_arg0))
> + return false;
> if (!is_factor_profitable (arg1_def_stmt, merge, new_arg1))
> return false;
> if (gimple_has_location (arg1_def_stmt))
> @@ -409,14 +553,20 @@ factor_out_conditional_operation (edge e0, edge e1,
> basic_block merge,
> locus = narg0_loc;
> }
> }
> + else if (arg0_op.num_ops != 1)
> + return false;
> else
> {
> + new_arg0 = arg0_op.ops[0];
> + opnum = 0;
> /* For constants only handle if the phi was the only one. */
> if (single_non_singleton_phi_for_edges (phi_nodes (merge), e0, e1) ==
> NULL)
> return false;
> /* TODO: handle more than just casts here. */
> if (!gimple_assign_cast_p (arg0_def_stmt))
> return false;
> + if (!is_factor_profitable (arg0_def_stmt, merge, new_arg0))
> + return false;
>
> /* arg0_def_stmt should be conditional. */
> if (dominated_by_p (CDI_DOMINATORS, gimple_bb (phi), gimple_bb
> (arg0_def_stmt)))
> @@ -509,7 +659,7 @@ factor_out_conditional_operation (edge e0, edge e1,
> basic_block merge,
> gimple_match_op new_op = arg0_op;
>
> /* Create the operation stmt if possible and insert it. */
> - new_op.ops[0] = temp;
> + new_op.ops[opnum] = temp;
> gimple_seq seq = NULL;
> result = maybe_push_res_to_seq (&new_op, &seq, result);
>
> @@ -4105,7 +4255,7 @@ pass_phiopt::execute (function *)
> gphi *phi = as_a <gphi *> (gsi_stmt (gsi));
>
> if (factor_out_conditional_operation (e1, e2, merge, phi,
> - cond_stmt))
> + cond_stmt, early_p))
> {
> /* Start over if there was an operation that was factored out because the
> new phi might have another opportunity. */
> phis = phi_nodes (merge);
> diff --git a/gcc/tree-ssa-phiopt.h b/gcc/tree-ssa-phiopt.h
> new file mode 100644
> index 00000000000..bba3136965d
> --- /dev/null
> +++ b/gcc/tree-ssa-phiopt.h
> @@ -0,0 +1,24 @@
> +/* Copyright (C) 2026 Free Software Foundation, Inc.
> +
> +This file is part of GCC.
> +
> +GCC is free software; you can redistribute it and/or modify it
> +under the terms of the GNU General Public License as published by the
> +Free Software Foundation; either version 3, or (at your option) any
> +later version.
> +
> +GCC is distributed in the hope that it will be useful, but WITHOUT
> +ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
> +FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
> +for more details.
> +
> +You should have received a copy of the GNU General Public License
> +along with GCC; see the file COPYING3. If not see
> +<http://www.gnu.org/licenses/>. */
> +
> +#ifndef TREE_SSA_PHIOPT_H
> +#define TREE_SSA_PHIOPT_H
> +extern int find_different_opnum (const gimple_match_op &arg0_op,
> + const gimple_match_op &arg1_op,
> + tree *new_arg0, tree *new_arg1);
> +#endif
> --
> 2.43.0
>
