>From 7a7c9a2a976fbb29f67c46284e7c1581cbe8cb07 Mon Sep 17 00:00:00 2001
From: Abhishek Kaushik <abhishek.kaus...@intel.com>
Date: Fri, 31 Jan 2025 01:28:48 -0800
Subject: [PATCH] libstdc++: Use canonical loop form in std::reduce
This change is for the INTEL C compiler (icx).
The current while loop in std::reduce and related functions is hard to
vectorize because the loop control variable is hard to detect in icx.
`while ((__last - __first) >= 4)`
Changing the loop header to a for loop following the OpenMP canonical
form allows easy vectorization, resulting in improved performance.
`for (; __first <= __last - 4; __first += 4)`
This patch modifies the loop header for std::reduce & std::transform_reduce.
---
libstdc++-v3/include/std/numeric | 10 +++-------
1 file changed, 3 insertions(+), 7 deletions(-)
diff --git a/libstdc++-v3/include/std/numeric b/libstdc++-v3/include/std/numeric
index 4d36fcd36d9..9c38ad89e21 100644
--- a/libstdc++-v3/include/std/numeric
+++ b/libstdc++-v3/include/std/numeric
@@ -300,13 +300,12 @@ namespace __detail
static_assert(is_invocable_r_v<_Tp, _BinaryOperation&, __ref, __ref>);
if constexpr (__is_random_access_iter<_InputIterator>::value)
{
- while ((__last - __first) >= 4)
+ for (; __first <= __last - 4; __first += 4)
{
_Tp __v1 = __binary_op(__first[0], __first[1]);
_Tp __v2 = __binary_op(__first[2], __first[3]);
_Tp __v3 = __binary_op(__v1, __v2);
__init = __binary_op(__init, __v3);
- __first += 4;
}
}
for (; __first != __last; ++__first)
@@ -381,7 +380,7 @@ namespace __detail
if constexpr (__and_v<__is_random_access_iter<_InputIterator1>,
__is_random_access_iter<_InputIterator2>>)
{
- while ((__last1 - __first1) >= 4)
+ for (; __first1 <= __last1 - 4; __first1 += 4, __first2 += 4)
{
_Tp __v1 = __binary_op1(__binary_op2(__first1[0], __first2[0]),
__binary_op2(__first1[1], __first2[1]));
@@ -389,8 +388,6 @@ namespace __detail
__binary_op2(__first1[3], __first2[3]));
_Tp __v3 = __binary_op1(__v1, __v2);
__init = __binary_op1(__init, __v3);
- __first1 += 4;
- __first2 += 4;
}
}
for (; __first1 != __last1; ++__first1, (void) ++__first2)
@@ -447,7 +444,7 @@ namespace __detail
{
if constexpr (__is_random_access_iter<_InputIterator>::value)
{
- while ((__last - __first) >= 4)
+ for (; __first <= __last - 4; __first += 4)
{
_Tp __v1 = __binary_op(__unary_op(__first[0]),
__unary_op(__first[1]));
@@ -455,7 +452,6 @@ namespace __detail
__unary_op(__first[3]));
_Tp __v3 = __binary_op(__v1, __v2);
__init = __binary_op(__init, __v3);
- __first += 4;
}
}
for (; __first != __last; ++__first)
--
2.31.1
________________________________
From: Abhishek Kaushik
Sent: Friday, January 31, 2025 4:28 PM
To: libstd...@gcc.gnu.org <libstd...@gcc.gnu.org>
Cc: gcc-patches@gcc.gnu.org <gcc-patches@gcc.gnu.org>
Subject: [PATCH] libstdc++: Use canonical loop form in std::reduce
>From 4ac7c7e56e23ed2f4dd2dafdfab6cfa110c14260 Mon Sep 17 00:00:00 2001
From: Abhishek Kaushik <abhishek.kaus...@intel.com>
Date: Fri, 31 Jan 2025 01:28:48 -0800
Subject: [PATCH] libstdc++: Use canonical loop form in std::reduce
The current while loop in std::reduce and related functions is hard to
vectorize because the loop control variable is hard to detect.
`while ((__last - __first) >= 4)`
Changing the loop header to a for loop following the OpenMP canonical
form allows easy vectorization, resulting in improved performance.
`for (; __first <= __last - 4; __first += 4)`
This patch modifies the loop header for std::reduce & std::transform_reduce.
---
libstdc++-v3/include/std/numeric | 10 +++-------
1 file changed, 3 insertions(+), 7 deletions(-)
diff --git a/libstdc++-v3/include/std/numeric b/libstdc++-v3/include/std/numeric
index 4d36fcd36d9..9c38ad89e21 100644
--- a/libstdc++-v3/include/std/numeric
+++ b/libstdc++-v3/include/std/numeric
@@ -300,13 +300,12 @@ namespace __detail
static_assert(is_invocable_r_v<_Tp, _BinaryOperation&, __ref, __ref>);
if constexpr (__is_random_access_iter<_InputIterator>::value)
{
- while ((__last - __first) >= 4)
+ for (; __first <= __last - 4; __first += 4)
{
_Tp __v1 = __binary_op(__first[0], __first[1]);
_Tp __v2 = __binary_op(__first[2], __first[3]);
_Tp __v3 = __binary_op(__v1, __v2);
__init = __binary_op(__init, __v3);
- __first += 4;
}
}
for (; __first != __last; ++__first)
@@ -381,7 +380,7 @@ namespace __detail
if constexpr (__and_v<__is_random_access_iter<_InputIterator1>,
__is_random_access_iter<_InputIterator2>>)
{
- while ((__last1 - __first1) >= 4)
+ for (; __first1 <= __last1 - 4; __first1 += 4, __first2 += 4)
{
_Tp __v1 = __binary_op1(__binary_op2(__first1[0], __first2[0]),
__binary_op2(__first1[1], __first2[1]));
@@ -389,8 +388,6 @@ namespace __detail
__binary_op2(__first1[3], __first2[3]));
_Tp __v3 = __binary_op1(__v1, __v2);
__init = __binary_op1(__init, __v3);
- __first1 += 4;
- __first2 += 4;
}
}
for (; __first1 != __last1; ++__first1, (void) ++__first2)
@@ -447,7 +444,7 @@ namespace __detail
{
if constexpr (__is_random_access_iter<_InputIterator>::value)
{
- while ((__last - __first) >= 4)
+ for (; __first <= __last - 4; __first += 4)
{
_Tp __v1 = __binary_op(__unary_op(__first[0]),
__unary_op(__first[1]));
@@ -455,7 +452,6 @@ namespace __detail
__unary_op(__first[3]));
_Tp __v3 = __binary_op(__v1, __v2);
__init = __binary_op(__init, __v3);
- __first += 4;
}
}
for (; __first != __last; ++__first)
--
2.31.1
