Re: [PATCH] Optimize macro: make it more predictable

["Martin Liška" <mliska@suse.cz>]

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On 10/23/20 1:47 PM, Martin Liška wrote:
> Hey.

Hello.

I deferred the patch for GCC 12. Since the time, I messed up with options
I feel more familiar with the option handling. So ...

> 
> This is a follow-up of the discussion that happened in thread about no_stack_protector
> attribute: https://gcc.gnu.org/pipermail/gcc-patches/2020-May/545916.html
> 
> The current optimize attribute works in the following way:
> - 1) we take current global_options as base
> - 2) maybe_default_options is called for the currently selected optimization level, which
>       means all rules in default_options_table are executed
> - 3) attribute values are applied (via decode_options)
> 
> So the step 2) is problematic: in case of -O2 -fno-omit-frame-pointer and __attribute__((optimize("-fno-stack-protector")))
> ends basically with -O2 -fno-stack-protector because -fno-omit-frame-pointer is default:
>      /* -O1 and -Og optimizations.  */
>      { OPT_LEVELS_1_PLUS, OPT_fomit_frame_pointer, NULL, 1 },
> 
> My patch handled and the current optimize attribute really behaves that same as appending attribute value
> to the command line. So far so good. We should also reflect that in documentation entry which is quite
> vague right now:

^^^ all these are still valid arguments, plus I'm adding a new test-case that tests that.

> 
> """
> The optimize attribute is used to specify that a function is to be compiled with different optimization options than specified on the command line.
> """

I addressed that with documentation changes, should be more clear to users. Moreover, I noticed that we declare 'optimize' attribute
as something not for a production use:

"The optimize attribute should be used for debugging purposes only. It is not suitable in production code."

Are we sure about the statement? I know that e.g. glibc uses that.

> 
> and we may want to handle -Ox in the attribute in a special way. I guess many macro/pragma users expect that
> 
> -O2 -ftree-vectorize and __attribute__((optimize(1))) will end with -O1 and not
> with -ftree-vectorize -O1 ?

The situation with 'target' attribute is different. When parsing the attribute, we intentionally drop all existing target flags:

$ cat -n gcc/config/i386/i386-options.c
...
   1245                if (opt == IX86_FUNCTION_SPECIFIC_ARCH)
   1246                  {
   1247                    /* If arch= is set,  clear all bits in x_ix86_isa_flags,
   1248                       except for ISA_64BIT, ABI_64, ABI_X32, and CODE16
   1249                       and all bits in x_ix86_isa_flags2.  */
   1250                    opts->x_ix86_isa_flags &= (OPTION_MASK_ISA_64BIT
   1251                                               | OPTION_MASK_ABI_64
   1252                                               | OPTION_MASK_ABI_X32
   1253                                               | OPTION_MASK_CODE16);
   1254                    opts->x_ix86_isa_flags_explicit &= (OPTION_MASK_ISA_64BIT
   1255                                                        | OPTION_MASK_ABI_64
   1256                                                        | OPTION_MASK_ABI_X32
   1257                                                        | OPTION_MASK_CODE16);
   1258                    opts->x_ix86_isa_flags2 = 0;
   1259                    opts->x_ix86_isa_flags2_explicit = 0;
   1260                  }

That seems logical because target attribute is used for e.g. ifunc multi-versioning and one needs
to be sure all existing ISA flags are dropped. However, I noticed clang behaves differently:

$ cat hreset.c
#pragma GCC target "arch=geode"
#include <immintrin.h>
void foo(unsigned int eax)
{
   _hreset (eax);
}

$ clang hreset.c -mhreset  -c -O2 -m32
$ gcc hreset.c -mhreset  -c -O2 -m32
In file included from /home/marxin/bin/gcc/lib64/gcc/x86_64-pc-linux-gnu/12.0.0/include/x86gprintrin.h:97,
                  from /home/marxin/bin/gcc/lib64/gcc/x86_64-pc-linux-gnu/12.0.0/include/immintrin.h:27,
                  from hreset.c:2:
hreset.c: In function ‘foo’:
/home/marxin/bin/gcc/lib64/gcc/x86_64-pc-linux-gnu/12.0.0/include/hresetintrin.h:39:1: error: inlining failed in call to ‘always_inline’ ‘_hreset’: target specific option mismatch
    39 | _hreset (unsigned int __EAX)
       | ^~~~~~~
hreset.c:5:3: note: called from here
     5 |   _hreset (eax);
       |   ^~~~~~~~~~~~~

Anyway, I think the current target attribute handling should be preserved.

Patch can bootstrap on x86_64-linux-gnu and survives regression tests.

Ready to be installed?
Thanks,
Martin

> 
> I'm also planning to take a look at the target macro/attribute, I expect similar problems:
> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97469
> 
> Thoughts?
> Thanks,
> Martin


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From eaa1892cbe32c6fe73de7708aa17be2d3917bceb Mon Sep 17 00:00:00 2001
From: Martin Liska <mliska@suse.cz>
Date: Wed, 2 Jun 2021 08:44:37 +0200
Subject: [PATCH] Append target/optimize attr to the current cmdline.

gcc/c-family/ChangeLog:

	* c-common.c (parse_optimize_options): Combine optimize
	options with what was provided on the command line.

gcc/ChangeLog:

	* toplev.c (toplev::main): Save decoded optimization options.
	* toplev.h (save_opt_decoded_options): New.
	* doc/extend.texi: Be more clear about optimize and target
	attributes.

gcc/testsuite/ChangeLog:

	* gcc.target/i386/avx512er-vrsqrt28ps-3.c: Disable fast math.
	* gcc.target/i386/avx512er-vrsqrt28ps-5.c: Likewise.
	* gcc.target/i386/attr-optimize.c: New test.
---
 gcc/c-family/c-common.c                       | 17 +++++++++++--
 gcc/doc/extend.texi                           |  8 +++++--
 gcc/testsuite/gcc.target/i386/attr-optimize.c | 24 +++++++++++++++++++
 .../gcc.target/i386/avx512er-vrsqrt28ps-3.c   |  2 +-
 .../gcc.target/i386/avx512er-vrsqrt28ps-5.c   |  2 +-
 gcc/toplev.c                                  |  8 +++++++
 gcc/toplev.h                                  |  1 +
 7 files changed, 56 insertions(+), 6 deletions(-)
 create mode 100644 gcc/testsuite/gcc.target/i386/attr-optimize.c

diff --git a/gcc/c-family/c-common.c b/gcc/c-family/c-common.c
index 681fcc972f4..f4e56653585 100644
--- a/gcc/c-family/c-common.c
+++ b/gcc/c-family/c-common.c
@@ -5901,9 +5901,22 @@ parse_optimize_options (tree args, bool attr_p)
       j++;
     }
   decoded_options_count = j;
-  /* And apply them.  */
+
+  /* Merge the decoded options with save_decoded_options.  */
+  unsigned save_opt_count = save_opt_decoded_options.length ();
+  unsigned merged_decoded_options_count
+    = save_opt_count + decoded_options_count;
+  cl_decoded_option *merged_decoded_options
+    = XNEWVEC (cl_decoded_option, merged_decoded_options_count);
+
+  for (unsigned i = 0; i < save_opt_count; ++i)
+    merged_decoded_options[i] = save_opt_decoded_options[i];
+  for (unsigned i = 0; i < decoded_options_count; ++i)
+    merged_decoded_options[save_opt_count + i] = decoded_options[i];
+
+   /* And apply them.  */
   decode_options (&global_options, &global_options_set,
-		  decoded_options, decoded_options_count,
+		  merged_decoded_options, merged_decoded_options_count,
 		  input_location, global_dc, NULL);
   free (decoded_options);
 
diff --git a/gcc/doc/extend.texi b/gcc/doc/extend.texi
index 8fc66d626d8..3b501a8be3a 100644
--- a/gcc/doc/extend.texi
+++ b/gcc/doc/extend.texi
@@ -3593,7 +3593,10 @@ take function pointer arguments.
 @cindex @code{optimize} function attribute
 The @code{optimize} attribute is used to specify that a function is to
 be compiled with different optimization options than specified on the
-command line.  Valid arguments are constant non-negative integers and
+command line.  The optimize attribute arguments of a function behave
+as if they were added to the command line options.
+
+Valid arguments are constant non-negative integers and
 strings.  Each numeric argument specifies an optimization @var{level}.
 Each @var{string} argument consists of one or more comma-separated
 substrings.  Each substring that begins with the letter @code{O} refers
@@ -3797,7 +3800,8 @@ This attribute prevents stack protection code for the function.
 Multiple target back ends implement the @code{target} attribute
 to specify that a function is to
 be compiled with different target options than specified on the
-command line.  One or more strings can be provided as arguments.
+command line.  The original target command line options are ignored.
+One or more strings can be provided as arguments.
 Each string consists of one or more comma-separated suffixes to
 the @code{-m} prefix jointly forming the name of a machine-dependent
 option.  @xref{Submodel Options,,Machine-Dependent Options}.
diff --git a/gcc/testsuite/gcc.target/i386/attr-optimize.c b/gcc/testsuite/gcc.target/i386/attr-optimize.c
new file mode 100644
index 00000000000..f5db028f1fd
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/attr-optimize.c
@@ -0,0 +1,24 @@
+/* { dg-do compile } */
+/* { dg-additional-options "-O1 -ftree-slp-vectorize -march=znver1 -fdump-tree-optimized" } */
+
+/* Use -O2, but -ftree-slp-vectorize option should be preserved and used.  */
+#pragma GCC optimize "-O2"
+
+typedef struct {
+  long n[4];
+} secp256k1_fe;
+
+void *a;
+int c;
+static void
+fn1(secp256k1_fe *p1, int p2)
+{
+  p1->n[0] = p1->n[1] = p2;
+}
+void
+fn2()
+{
+  fn1(a, !c);
+}
+
+/* { dg-final { scan-tree-dump { MEM <vector\(2\) long int> \[[^]]*\] = } "optimized" } } */
diff --git a/gcc/testsuite/gcc.target/i386/avx512er-vrsqrt28ps-3.c b/gcc/testsuite/gcc.target/i386/avx512er-vrsqrt28ps-3.c
index 1ba8172d6e3..40aefb50844 100644
--- a/gcc/testsuite/gcc.target/i386/avx512er-vrsqrt28ps-3.c
+++ b/gcc/testsuite/gcc.target/i386/avx512er-vrsqrt28ps-3.c
@@ -8,7 +8,7 @@
 #define MAX 1000
 #define EPS 0.00001
 
-__attribute__ ((noinline, optimize (1)))
+__attribute__ ((noinline, optimize (1, "-fno-fast-math")))
 void static
 compute_rsqrt_ref (float *a, float *r)
 {
diff --git a/gcc/testsuite/gcc.target/i386/avx512er-vrsqrt28ps-5.c b/gcc/testsuite/gcc.target/i386/avx512er-vrsqrt28ps-5.c
index e067a81e562..498f4d50aa5 100644
--- a/gcc/testsuite/gcc.target/i386/avx512er-vrsqrt28ps-5.c
+++ b/gcc/testsuite/gcc.target/i386/avx512er-vrsqrt28ps-5.c
@@ -8,7 +8,7 @@
 #define MAX 1000
 #define EPS 0.00001
 
-__attribute__ ((noinline, optimize (1)))
+__attribute__ ((noinline, optimize (1, "-fno-fast-math")))
 void static
 compute_sqrt_ref (float *a, float *r)
 {
diff --git a/gcc/toplev.c b/gcc/toplev.c
index 43f1f7d345e..3e26ad97ff0 100644
--- a/gcc/toplev.c
+++ b/gcc/toplev.c
@@ -121,6 +121,9 @@ static bool no_backend;
 struct cl_decoded_option *save_decoded_options;
 unsigned int save_decoded_options_count;
 
+/* Vector of saved Optimization decoded command line options.  */
+auto_vec<cl_decoded_option> save_opt_decoded_options;
+
 /* Used to enable -fvar-tracking, -fweb and -frename-registers according
    to optimize in process_options ().  */
 #define AUTODETECT_VALUE 2
@@ -2335,6 +2338,11 @@ toplev::main (int argc, char **argv)
 						&save_decoded_options,
 						&save_decoded_options_count);
 
+  /* Save Optimization decoded options.  */
+  for (unsigned i = 0; i < save_decoded_options_count; ++i)
+    if (cl_options[save_decoded_options[i].opt_index].flags & CL_OPTIMIZATION)
+      save_opt_decoded_options.safe_push (save_decoded_options[i]);
+
   /* Perform language-specific options initialization.  */
   lang_hooks.init_options (save_decoded_options_count, save_decoded_options);
 
diff --git a/gcc/toplev.h b/gcc/toplev.h
index 175944c85b7..9a1d2e6986f 100644
--- a/gcc/toplev.h
+++ b/gcc/toplev.h
@@ -23,6 +23,7 @@ along with GCC; see the file COPYING3.  If not see
 /* Decoded options, and number of such options.  */
 extern struct cl_decoded_option *save_decoded_options;
 extern unsigned int save_decoded_options_count;
+extern auto_vec<cl_decoded_option> save_opt_decoded_options;
 
 class timer;
 
-- 
2.32.0