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[PATCH] reduce size penalty for including C++11 <algorithm> on x86 systems
- From: Nathan Froyd <froydnj at mozilla dot com>
- To: gcc-patches at gcc dot gnu dot org, libstdc++ at gcc dot gnu dot org
- Date: Tue, 13 Oct 2015 21:44:19 -0400
- Subject: [PATCH] reduce size penalty for including C++11 <algorithm> on x86 systems
- Authentication-results: sourceware.org; auth=none
From: Nathan Froyd <froydnj@gmail.com>
Including <algorithm> in C++11 mode (typically done for
std::{min,max,swap}) includes <random>, for
std::uniform_int_distribution. On x86 platforms, <random> manages to
drag in <x86intrin.h> through x86's opt_random.h header, and
<x86intrin.h> has gotten rather large recently with the addition of AVX
intrinsics. The comparison between C++03 mode and C++11 mode is not
quite exact, but it gives an idea of the penalty we're talking about
here:
froydnj@thor:~/src$ echo '#include <algorithm>' | g++ -x c++ - -o - -E -std=c++11 | wc
53460 127553 1401268
froydnj@thor:~/src$ echo '#include <algorithm>' | g++ -x c++ - -o - -E -std=c++03 | wc
9202 18933 218189
That's approximately a 7x penalty in C++11 mode (granted, C++11 includes
more than just <x86intrin.h>) with GCC 4.9.2 on a Debian system; current
mainline is somewhat worse:
froydnj@thor: gcc-build$ echo '#include <algorithm>' | xgcc [...] -std=c++11 | wc
84851 210475 2369616
froydnj@thor: gcc-build$ echo '#include <algorithm>' | xgcc [...] -std=c++03 | wc
9383 19402 239676
<x86intrin.h> itself clocks in at 1.3MB+ of preprocessed text.
This patch aims to reduce that size penalty by recognizing that both of
the places that #include <x86intrin.h> do not need the full set of x86
intrinsics, but can get by with a smaller, more focused header in each
case. <ext/random> needs only <emmintrin.h> to declare __m128i, while
x86's opt_random.h must include <pmmintrin.h> for declarations of
various intrinsic functions.
The net result is that the size of mainline's <algorithm> is significantly reduced:
froydnj@thor: gcc-build$ echo '#include <algorithm>' | xgcc [...] -std=c++11 | wc
39174 88538 1015281
which seems like a win.
Bootstrapped on x86_64-pc-linux-gnu with --enable-languages=c,c++,
tested with check-target-libstdc++-v3, no regressions. Also verified
that <algorithm> and <ext/random> pass -fsyntax-check with
-march=native (on a recent Haswell chip); if an -march=native bootstrap
is necessary, I am happy to do that if somebody instructs me in getting
everything properly set up.
OK?
-Nathan
* config/cpu/i486/opt/bits/opt_random.h: Include pmmintrin.h instead
of x86intrin.h, and only do so when __SSE3__
* include/ext/random: Include emmintrin.h instead of x86intrin.h
---
libstdc++-v3/ChangeLog | 6 ++++++
libstdc++-v3/config/cpu/i486/opt/bits/opt_random.h | 4 +++-
libstdc++-v3/include/ext/random | 2 +-
3 files changed, 10 insertions(+), 2 deletions(-)
diff --git a/libstdc++-v3/ChangeLog b/libstdc++-v3/ChangeLog
index e3061ef..ff0b048 100644
--- a/libstdc++-v3/ChangeLog
+++ b/libstdc++-v3/ChangeLog
@@ -1,3 +1,9 @@
+2015-10-13 Nathan Froyd <froydnj@gcc.gnu.org>
+
+ * config/cpu/i486/opt/bits/opt_random.h: Include pmmintrin.h instead
+ of x86intrin.h, and only do so when __SSE3__
+ * include/ext/random: Include emmintrin.h instead of x86intrin.h
+
2015-10-11 Joseph Myers <joseph@codesourcery.com>
* crossconfig.m4 (GLIBCXX_CROSSCONFIG) <*-linux* | *-uclinux* |
diff --git a/libstdc++-v3/config/cpu/i486/opt/bits/opt_random.h b/libstdc++-v3/config/cpu/i486/opt/bits/opt_random.h
index 4495569..a9f6c13 100644
--- a/libstdc++-v3/config/cpu/i486/opt/bits/opt_random.h
+++ b/libstdc++-v3/config/cpu/i486/opt/bits/opt_random.h
@@ -30,7 +30,9 @@
#ifndef _BITS_OPT_RANDOM_H
#define _BITS_OPT_RANDOM_H 1
-#include <x86intrin.h>
+#ifdef __SSE3__
+#include <pmmintrin.h>
+#endif
#pragma GCC system_header
diff --git a/libstdc++-v3/include/ext/random b/libstdc++-v3/include/ext/random
index 0bcfa4a..ba363ce 100644
--- a/libstdc++-v3/include/ext/random
+++ b/libstdc++-v3/include/ext/random
@@ -40,7 +40,7 @@
#include <array>
#include <ext/cmath>
#ifdef __SSE2__
-# include <x86intrin.h>
+# include <emmintrin.h>
#endif
#if defined(_GLIBCXX_USE_C99_STDINT_TR1) && defined(UINT32_C)
--
2.1.4