On 8/5/2026 5:53 AM, [email protected] wrote:
From: Kyrylo Tkachov <[email protected]>
The minimum and the maximum of two values add up to the sum of those
values, so subtracting one of them from the sum yields the other one.
That identity holds in modular arithmetic. It also holds for floating
point when reassociation is enabled and signed zeros and traps are not
honoured.
int f (int a, int b) { int mn = a < b ? a : b; return (a + b) - mn; }
aarch64 -O2:
before after
cmp w1, w0 cmp w1, w0
add w2, w1, w0 csel w0, w1, w0, ge
csel w0, w1, w0, le
sub w0, w2, w0
Bootstrapped and tested on aarch64-none-linux-gnu.
Ok for trunk?
Thanks,
Kyrill
gcc/ChangeLog:
* match.pd ((x + y) - minmax (x, y)): New simplification.
gcc/testsuite/ChangeLog:
* gcc.dg/tree-ssa/minmax-sum-1.c: New test.
* gcc.dg/tree-ssa/minmax-sum-fp-1.c: Likewise.
* gcc.dg/tree-ssa/minmax-sum-fp-2.c: Likewise.
* g++.target/aarch64/minmax-sum-1.C: Likewise.
Signed-off-by: Kyrylo Tkachov <[email protected]>
---
gcc/match.pd | 15 +++++++++++++++
.../g++.target/aarch64/minmax-sum-1.C | 17 +++++++++++++++++
gcc/testsuite/gcc.dg/tree-ssa/minmax-sum-1.c | 18 ++++++++++++++++++
.../gcc.dg/tree-ssa/minmax-sum-fp-1.c | 15 +++++++++++++++
.../gcc.dg/tree-ssa/minmax-sum-fp-2.c | 10 ++++++++++
5 files changed, 75 insertions(+)
create mode 100644 gcc/testsuite/g++.target/aarch64/minmax-sum-1.C
create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/minmax-sum-1.c
create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/minmax-sum-fp-1.c
create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/minmax-sum-fp-2.c
diff --git a/gcc/match.pd b/gcc/match.pd
index 728fa8a8d63..35cc995ebf9 100644
--- a/gcc/match.pd
+++ b/gcc/match.pd
@@ -2051,6 +2051,21 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
&& !TYPE_SATURATING (type))
(res @0 @1))))
+/* (x + y) - min (x, y) -> max (x, y)
+ (x + y) - max (x, y) -> min (x, y)
+ The sum of the minimum and the maximum is the sum of the operands. */
+(for minmax (min max)
+ maxmin (max min)
+ (simplify
+ (minus (plus @0 @1) (minmax @0 @1))
+ (if ((ANY_INTEGRAL_TYPE_P (type)
+ && !TYPE_OVERFLOW_SANITIZED (type) && !TYPE_OVERFLOW_TRAPS (type))
+ || (FLOAT_TYPE_P (type)
+ && flag_associative_math
+ && !HONOR_SIGNED_ZEROS (type)
+ && !flag_trapping_math))
+ (maxmin @0 @1))))
+
LOL. I was going to suggest a :c on the plus and minmax expressions,
but it looks like that was something Andrea explicitly indicated you
didn't need :-)
OK for the trunk.
jeffh
