Add pgo build type

One of the ways we can optimize our builds is with profile guided
optimization.  This entails doing several things:

1) Building with --coverage
2) Running an application against the openssl library from step (1) to
   generate profile data
3) rebuilding openssl using the input profile from step (2) to optimize
   the build.

This new build configuration will let developers use the profiled data
to see what type of optimizations might be possible, as well as giving
end users the ability to squeeze a bit more performance out of openssl

Reviewed-by: Tomas Mraz <tomas@openssl.org>
Reviewed-by: Paul Dale <ppzgs1@gmail.com>
(Merged from https://github.com/openssl/openssl/pull/27839)

Configurations/10-main.conf

@@ -679,7 +679,9 @@ my %targets = (
         CXX              => "g++",
         CFLAGS           => picker(default => "-Wall",
                                    debug   => "-O0 -g",
-                                   release => "-O3"),
+                                   release => "-O3",
+                                   profiled => "-O3 -fprofile-generate -fprofile-arcs -fprofile-values -ftest-coverage",
+                                   pgo => "-O3 -fprofile-use -Wno-missing-profile"),
         CXXFLAGS         => picker(default => "-Wall",
                                    debug   => "-O0 -g",
                                    release => "-O3"),

Configure

@@ -990,6 +990,10 @@ while (@argvcopy)
                 {
                 $config{build_type} = "debug";
                 }
+        elsif (/^-p$/)
+                {
+                $config{build_type} = "profiled";
+                }
         elsif (/^-v$/)          # From older 'config'
                 {
                 $guess_opts{verbose} = 1;
@@ -1017,6 +1021,14 @@ while (@argvcopy)
                 {
                 $config{build_type} = "release";
                 }
+        elsif (/^--profiled$/)
+                {
+                $config{build_type} = "profiled";
+                }
+        elsif (/^--pgo$/)
+                {
+                $config{build_type} = "pgo";
+                }
         elsif (/^386$/)
                 { $config{processor}=386; }
         elsif (/^rsaref$/)

INSTALL.md

@@ -335,6 +335,14 @@ Build OpenSSL with debugging symbols and zero optimization level.
 
 Build OpenSSL without debugging symbols.  This is the default.
 
+    --coverage
+
+Build OpenSSL with gcov profiling information included
+
+    --pgo
+
+Build OpenSSL optimized using gcov data obtained from --coverage build
+
 Directories
 -----------
 
@@ -2033,6 +2041,24 @@ around the problem by forcing the build procedure to use the following script:
 instead of the real clang. In which case it doesn't matter what clang version
 is used, as it is the version of the GNU assembler that will be checked.
 
+Notes on profile guided optimization
+------------------------------------
+
+Some compilers support the concept of profile guided optimization.  This feature
+allows a user to build openssl and use profiling data gathered while running an
+application such that it can then be rebuilt in a way that is optimized specifically
+for that application, increasing performance.  Currently this feature is built into
+the openssl build system for x86_64 only.
+
+1) Configure openssl with the --coverage option.  This will configure the compiler to
+   record profiling data for the libcrypto and libssl libraries
+2) Run the application(s) which you wish to optimize for, ensuring that they use
+   the libraries compiled in step (1) (note this may entail the use of LD_LIBRARY_PATH)
+3) Clean the openssl build with make clean.  Note that the profile data (the .gcda and .gcno
+   files are retained through the clean operation). This is intentional.
+4) Configure openssl again, but this time select the --pgo build type.  This will use the
+   profiled data to optimize code layout for the application in question.
+
 ---
 
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