159 lines
6.2 KiB
Diff
159 lines
6.2 KiB
Diff
From 441d0aa048a51d2e9c4f4227916d2a1a2f06b4e5 Mon Sep 17 00:00:00 2001
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From: Jan Hubicka <jh@suse.cz>
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Date: Wed, 24 Jan 2024 18:13:17 +0100
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Subject: [PATCH] Add -fmin-function-alignmnet
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To: gcc-patches@gcc.gnu.org
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-falign-functions is ignored in cold code, since it is an optimization intended to
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improve instruction prefetch. In some case it is necessary to force alignment for
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all functions, so this patch adds -fmin-function-alignment for this purpose.
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gcc/ChangeLog:
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PR middle-end/88345
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* common.opt: (flimit-function-alignment): Reorder alphabeticaly
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(fmin-function-alignment): New parameter.
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* doc/invoke.texi: (-fmin-function-alignment): Document.
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(-falign-functions,-falign-loops,-falign-labels): Mention that
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aglinments are ignored in cold code.
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* varasm.cc (assemble_start_function): Handle min-function-alignment.
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* lto-streamer.h (LTO_minor_version): Bump.
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---
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gcc/common.opt | 10 +++++++---
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gcc/doc/invoke.texi | 18 +++++++++++++++++-
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gcc/lto-streamer.h | 2 +-
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gcc/varasm.cc | 5 +++++
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4 files changed, 30 insertions(+), 5 deletions(-)
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diff --git a/gcc/common.opt b/gcc/common.opt
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index 862c474d3c8..5d35391b99f 100644
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--- a/gcc/common.opt
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+++ b/gcc/common.opt
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@@ -1027,9 +1027,6 @@ Align the start of functions.
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falign-functions=
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Common RejectNegative Joined Var(str_align_functions) Optimization
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-flimit-function-alignment
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-Common Var(flag_limit_function_alignment) Optimization Init(0)
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-
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falign-jumps
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Common Var(flag_align_jumps) Optimization
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Align labels which are only reached by jumping.
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@@ -2165,6 +2162,10 @@ fmessage-length=
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Common RejectNegative Joined UInteger
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-fmessage-length=<number> Limit diagnostics to <number> characters per line. 0 suppresses line-wrapping.
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+fmin-function-alignment=
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+Common Joined RejectNegative UInteger Var(flag_min_function_alignment) Optimization
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+Align the start of every function.
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+
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fmodulo-sched
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Common Var(flag_modulo_sched) Optimization
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Perform SMS based modulo scheduling before the first scheduling pass.
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@@ -2489,6 +2490,9 @@ starts and when the destructor finishes.
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flifetime-dse=
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Common Joined RejectNegative UInteger Var(flag_lifetime_dse) Optimization IntegerRange(0, 2)
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+flimit-function-alignment
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+Common Var(flag_limit_function_alignment) Optimization Init(0)
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+
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flive-patching
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Common RejectNegative Alias(flive-patching=,inline-clone) Optimization
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diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
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index b777fc92755..d39cb26326c 100644
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--- a/gcc/doc/invoke.texi
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+++ b/gcc/doc/invoke.texi
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@@ -531,6 +531,7 @@ Objective-C and Objective-C++ Dialects}.
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-falign-jumps[=@var{n}[:@var{m}:[@var{n2}[:@var{m2}]]]]
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-falign-labels[=@var{n}[:@var{m}:[@var{n2}[:@var{m2}]]]]
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-falign-loops[=@var{n}[:@var{m}:[@var{n2}[:@var{m2}]]]]
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+-fmin-function-alignment=[@var{n}]
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-fno-allocation-dce -fallow-store-data-races
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-fassociative-math -fauto-profile -fauto-profile[=@var{path}]
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-fauto-inc-dec -fbranch-probabilities
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@@ -13650,6 +13651,9 @@ Align the start of functions to the next power-of-two greater than or
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equal to @var{n}, skipping up to @var{m}-1 bytes. This ensures that at
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least the first @var{m} bytes of the function can be fetched by the CPU
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without crossing an @var{n}-byte alignment boundary.
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+This is an optimization of code performance and alignment is ignored for
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+functions considered cold. If alignment is required for all functions,
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+use @option{-fmin-function-alignment}.
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If @var{m} is not specified, it defaults to @var{n}.
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@@ -13713,6 +13717,8 @@ Enabled at levels @option{-O2}, @option{-O3}.
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Align loops to a power-of-two boundary. If the loops are executed
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many times, this makes up for any execution of the dummy padding
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instructions.
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+This is an optimization of code performance and alignment is ignored for
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+loops considered cold.
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If @option{-falign-labels} is greater than this value, then its value
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is used instead.
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@@ -13735,6 +13741,8 @@ Enabled at levels @option{-O2}, @option{-O3}.
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Align branch targets to a power-of-two boundary, for branch targets
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where the targets can only be reached by jumping. In this case,
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no dummy operations need be executed.
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+This is an optimization of code performance and alignment is ignored for
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+jumps considered cold.
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If @option{-falign-labels} is greater than this value, then its value
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is used instead.
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@@ -13748,6 +13756,14 @@ The maximum allowed @var{n} option value is 65536.
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Enabled at levels @option{-O2}, @option{-O3}.
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+@opindex fmin-function-alignment=@var{n}
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+@item -fmin-function-alignment
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+Specify minimal alignment of functions to the next power-of-two greater than or
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+equal to @var{n}. Unlike @option{-falign-functions} this alignment is applied
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+also to all functions (even those considered cold). The alignment is also not
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+affected by @option{-flimit-function-alignment}
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+
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+
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@opindex fno-allocation-dce
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@item -fno-allocation-dce
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Do not remove unused C++ allocations in dead code elimination.
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@@ -13844,7 +13860,7 @@ To use the link-time optimizer, @option{-flto} and optimization
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options should be specified at compile time and during the final link.
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It is recommended that you compile all the files participating in the
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same link with the same options and also specify those options at
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-link time.
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+link time.
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For example:
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@smallexample
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diff --git a/gcc/lto-streamer.h b/gcc/lto-streamer.h
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index 75cebcd02d3..2827897cc7a 100644
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--- a/gcc/lto-streamer.h
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+++ b/gcc/lto-streamer.h
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@@ -122,7 +122,7 @@ along with GCC; see the file COPYING3. If not see
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form followed by the data for the string. */
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#define LTO_major_version GCC_major_version
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-#define LTO_minor_version 1
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+#define LTO_minor_version 2
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typedef unsigned char lto_decl_flags_t;
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diff --git a/gcc/varasm.cc b/gcc/varasm.cc
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index cd0cd88321c..5de821b63e6 100644
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--- a/gcc/varasm.cc
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+++ b/gcc/varasm.cc
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@@ -1914,6 +1914,11 @@ assemble_start_function (tree decl, const char *fnname)
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/* Tell assembler to move to target machine's alignment for functions. */
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align = floor_log2 (align / BITS_PER_UNIT);
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+ /* Handle forced alignment. This really ought to apply to all functions,
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+ since it is used by patchable entries. */
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+ if (flag_min_function_alignment)
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+ align = MAX (align, floor_log2 (flag_min_function_alignment));
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+
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if (align > 0)
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{
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ASM_OUTPUT_ALIGN (asm_out_file, align);
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--
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2.35.3
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