From: Reshma Roy <[email protected]>
gcc/ChangeLog:
PR tree-optimization/126646
* match.pd: Fold umin(a, 1) | umin(b, 1) into umin(a | b, 1).
gcc/testsuite/ChangeLog:
* gcc.dg/tree-ssa/pr126646-1.c: New test.
* gcc.dg/tree-ssa/pr126646-2.c: New test.
---
Hi,
The patch is updated as per the comments and added a new test case for
the same. My comments are added inline to the email.
Bootstrapped and tested on x86_64-linux
> -----Original Message-----
> From: Andrea Pinski <[email protected]>
> Sent: Wednesday, August 12, 2026 9:59 AM
> To: Roy, Reshma <[email protected]>
> Cc: [email protected]; Kumar, Venkataramanan
> <[email protected]>
> Subject: Re: [PATCH] match.pd: Fold umin(a, 1) | umin(b, 1) into umin(a | b,
> 1)
> [PR126646]
>
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>
> On Tue, Aug 11, 2026 at 8:50???PM <[email protected]> wrote:
> >
> > From: Reshma Roy <[email protected]>
> >
> > gcc/ChangeLog:
> >
> > PR tree-optimization/126646
> > * match.pd: Fold umin(a, 1) | umin(b, 1) into umin(a | b, 1).
> >
> > gcc/testsuite/ChangeLog:
> >
> > * gcc.dg/tree-ssa/pr126646-1.c: New test.
> > ---
> >
> > Hi,
> > This patch fixes the missed optimization opportunity reported in
> > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=126646.
> > For the following snippet of code, gcc generates 2 MIN_EXPR.
> > unsigned f(unsigned a, unsigned b)
> > {
> > unsigned t = 1;
> > a = a < t ? a : t;
> > b = b < t ? b : t;
> > return a | b;
> > }
> > But this can be optimized with just one MIN_EXPR since
> > umin(a,1) | umin(b,1) can be simplified to umin(a|b, 1).
> >
> > Bootstrapped and tested on x86_64-linux.
> >
> > Thanks,
> > Reshma
> >
> > gcc/match.pd | 5 +++++
> > gcc/testsuite/gcc.dg/tree-ssa/pr126646-1.c | 15 +++++++++++++++
> > 2 files changed, 20 insertions(+)
> > create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/pr126646-1.c
> >
> > diff --git a/gcc/match.pd b/gcc/match.pd index
> > 50e73177022..7347b83ec4f 100644
> > --- a/gcc/match.pd
> > +++ b/gcc/match.pd
> > @@ -4860,6 +4860,11 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
> > (bit_not (minmax:cs (bit_not @0) @1))
> > (maxmin @0 (bit_not @1))))
> >
> > +/* umin (a, 1) | umin (b, 1) -> umin (a | b, 1). */ (simplify
> > + (bit_ior (min @0 integer_onep@2) (min @1 @2))
> > + (if (TYPE_UNSIGNED (type))
>
> Instead of TYPE_UNSIGNED here; I think it might be a good idea to use
> tree_expr_nonnegative_p on both @0 and @1..
> tree_expr_nonnegative_p does return true for TYPE_UNSIGNED already but it also
> returns true when the argument is known to be zero or positive.
Agreed, updated to use tree_expr_nonnegative_p (@0) &&
tree_expr_nonnegative_p (@1). This is strictly more general as it covers
unsigned types (where tree_expr_nonnegative_p returns true by definition) and
also signed types when the operands are non-negative.
>
> This allows for say:
> ```
> int f(int a, int b)
> {
> int c = 0;
> if (a >= 0 && b >= 0)
> c = (a > 1 ? 1 : a) | (b > 1 ? 1 : b);
> return c;
> }
> ```
Understood the test case scenario. But the above test case doesn't apply the
new guard in practice because by the time match.pd sees the MIN_EXPRs, the
condition a >= 0 && b >= 0 has already been folded into (a | b) >= 0. The
dominating condition is now on the combined OR, so tree_expr_nonnegative_p
on a and b individually can't prove non-negativity. Hence I have added a
different test case (pr126646-2.c) that uses __builtin_abs, where non-negativity
is implied in the expression itself. Hope that is fine. Let me know your
thoughts.
> Which then should optimize to just:
> _10 = a_6(D) | b_7(D);
> c_8 = MIN_EXPR <_10, 1>;
> _11 = MAX_EXPR <c_8, 0>;
>
>
> Thanks,
> Andrea
>
> > + (min (bit_ior @0 @1) @2)))
> > /* MIN (X, Y) == X -> X <= Y */
> > /* MIN (X, Y) < X -> X > Y */
> > /* MIN (X, Y) >= X -> X <= Y */
> > diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr126646-1.c
> > b/gcc/testsuite/gcc.dg/tree-ssa/pr126646-1.c
> > new file mode 100644
> > index 00000000000..447a1739b5f
> > --- /dev/null
> > +++ b/gcc/testsuite/gcc.dg/tree-ssa/pr126646-1.c
> > @@ -0,0 +1,15 @@
> > +/* { dg-do compile } */
> > +/* { dg-options "-O2 -fdump-tree-optimized" } */
> > +
> > +/* The test case should produce only one min expr. */
> > +/* umin(a,1) | umin(b,1) -> umin(a|b, 1). */
> > +
> > +unsigned min_or (unsigned a, unsigned b) {
> > + unsigned t = 1;
> > + a = a < t ? a : t;
> > + b = b < t ? b : t;
> > + return a | b;
> > +}
> > +
> > +/* { dg-final { scan-tree-dump-times "MIN_EXPR" 1 "optimized" } } */
> > --
> > 2.34.1
> >
Thanks,
Reshma
gcc/match.pd | 5 +++++
gcc/testsuite/gcc.dg/tree-ssa/pr126646-1.c | 15 +++++++++++++++
gcc/testsuite/gcc.dg/tree-ssa/pr126646-2.c | 13 +++++++++++++
3 files changed, 33 insertions(+)
create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/pr126646-1.c
create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/pr126646-2.c
diff --git a/gcc/match.pd b/gcc/match.pd
index 5fc89426880..be2bc0dd8df 100644
--- a/gcc/match.pd
+++ b/gcc/match.pd
@@ -4887,6 +4887,11 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
(bit_not (minmax:cs (bit_not @0) @1))
(maxmin @0 (bit_not @1))))
+/* umin (a, 1) | umin (b, 1) -> umin (a | b, 1). */
+ (simplify
+ (bit_ior (min @0 integer_onep@2) (min @1 @2))
+ (if (tree_expr_nonnegative_p (@0) && tree_expr_nonnegative_p (@1))
+ (min (bit_ior @0 @1) @2)))
/* MIN (X, Y) == X -> X <= Y */
/* MIN (X, Y) < X -> X > Y */
/* MIN (X, Y) >= X -> X <= Y */
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr126646-1.c
b/gcc/testsuite/gcc.dg/tree-ssa/pr126646-1.c
new file mode 100644
index 00000000000..447a1739b5f
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/pr126646-1.c
@@ -0,0 +1,15 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-optimized" } */
+
+/* The test case should produce only one min expr. */
+/* umin(a,1) | umin(b,1) -> umin(a|b, 1). */
+
+unsigned min_or (unsigned a, unsigned b)
+{
+ unsigned t = 1;
+ a = a < t ? a : t;
+ b = b < t ? b : t;
+ return a | b;
+}
+
+/* { dg-final { scan-tree-dump-times "MIN_EXPR" 1 "optimized" } } */
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr126646-2.c
b/gcc/testsuite/gcc.dg/tree-ssa/pr126646-2.c
new file mode 100644
index 00000000000..3b47eee9656
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/pr126646-2.c
@@ -0,0 +1,13 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-optimized" } */
+
+int f (int a, int b)
+{
+ int x = __builtin_abs (a);
+ int y = __builtin_abs (b);
+ int p = x < 1 ? x : 1;
+ int q = y < 1 ? y : 1;
+ return p | q;
+}
+
+/* { dg-final { scan-tree-dump-times "MIN_EXPR" 1 "optimized" } } */
--
2.34.1
