Merge bitcoin/bitcoin#23152: build: add `--enable-lto` configuration option

68e5aafde3e87c16da95410a0474f38f589afb36 build: add `--enable-lto` configuration option (fanquake)

Pull request description:

  It's been 5 years since using LTO was first suggested for use when building Bitcoin Core, and it's time to revisit it again. Compilers, and their LTO implementations, have matured, and Bitcoin Core has come a long way in terms of pruning dependencies which may have proved troublesome (i.e Boost previously had issues when using LTO). We'll have even less Boost code after moving to `std::filesystem` (#20744).

  Experimenting with LTO came up on IRC last night:
  > sipa: jamesob: i'm interested in knowing whether "-flto" and/or "-fdata-sections -ffunction-sections -Wl,--gc-sections" are possible/beneficial with our current compiler suite; what would be a good way to have your test infrastructure benchmark things?

  So this PR just adds the bare minimum to make it easier to configure, compile and perform some bench-marking using `-flto`. This PR doesn't do anything depends wise, however if we decide this is what we want to do, I'll expand the changes here.

  I had previously had a PR open (#18605) to perform link time garbage collection (`-ffunction-sections -fdata-sections` & `-Wl,--gc-sections`), however moving straight to using LTO would be preferable.

  Note that our minimum required set of compilers, GCC 8.1 and Clang 7, all support the `-flto` option.

  Related #18579.
  Previous discussion: #10616, #14277.
  Previous related PRs: #10800 (`-flto`), #16791 (ThinLTO).

  Guix build:
  ```bash
  bash-5.1# find guix-build-$(git rev-parse --short=12 HEAD)/output/ -type f -print0 | env LC_ALL=C sort -z | xargs -r0 sha256sum
  1f3a7c5be4169aaa444b481d3e65a7bb72da9007fee6e6c416ded2e70f97374b  guix-build-68e5aafde3e8/output/aarch64-linux-gnu/SHA256SUMS.part
  fa8f4cf223d9aaf0b2c1ef55ce61256a19cd1ad7f42b99d0b98c9a52fe6ad8ba  guix-build-68e5aafde3e8/output/aarch64-linux-gnu/bitcoin-68e5aafde3e8-aarch64-linux-gnu-debug.tar.gz
  9a9967078cd1849b4e85db619e1f55d305c6d44e9e013067c0e8d62c1ba54087  guix-build-68e5aafde3e8/output/aarch64-linux-gnu/bitcoin-68e5aafde3e8-aarch64-linux-gnu.tar.gz
  18c71f30722102baaf3dfda67f7c7aac38723510b142e8df8ee7063c5d499368  guix-build-68e5aafde3e8/output/arm-linux-gnueabihf/SHA256SUMS.part
  0854cc0d17c045a118df2a24e4cf36d727e7e7e2dea37c2492ee21b71cb79b4b  guix-build-68e5aafde3e8/output/arm-linux-gnueabihf/bitcoin-68e5aafde3e8-arm-linux-gnueabihf-debug.tar.gz
  215256897dde4e8412ed60473376c694a80c5479fb08039107fb62435f2816ef  guix-build-68e5aafde3e8/output/arm-linux-gnueabihf/bitcoin-68e5aafde3e8-arm-linux-gnueabihf.tar.gz
  5fad0d9d12bc514ec46ed5d66fd29b7da1376a4a69c3b692936f1ab2356e2f85  guix-build-68e5aafde3e8/output/dist-archive/bitcoin-68e5aafde3e8.tar.gz
  4f32989d4ab1946048ca7caee9a983fa875be262282562f5a3e040f4bf92158e  guix-build-68e5aafde3e8/output/powerpc64-linux-gnu/SHA256SUMS.part
  ae45df309ae8ada52891efac0a369a69fed4ab93847a7bc4150a62230df4c8d7  guix-build-68e5aafde3e8/output/powerpc64-linux-gnu/bitcoin-68e5aafde3e8-powerpc64-linux-gnu-debug.tar.gz
  0ced227de15cb578567131271e2effe80681b4d7a436c92bf1caec735a576fa4  guix-build-68e5aafde3e8/output/powerpc64-linux-gnu/bitcoin-68e5aafde3e8-powerpc64-linux-gnu.tar.gz
  26fc5d2ccc1bc17ee0a146cacada6f4909d90c136ae640c8337332adce414ee0  guix-build-68e5aafde3e8/output/powerpc64le-linux-gnu/SHA256SUMS.part
  9956b544d90a62a8ba9fc9dc6b6b7f0efe193357332ec19e88053a89d4aab37e  guix-build-68e5aafde3e8/output/powerpc64le-linux-gnu/bitcoin-68e5aafde3e8-powerpc64le-linux-gnu-debug.tar.gz
  be8e39ceea1d36086ce5fa93bfb138c68d3bdf0dd6950b192dfa27a65cce3836  guix-build-68e5aafde3e8/output/powerpc64le-linux-gnu/bitcoin-68e5aafde3e8-powerpc64le-linux-gnu.tar.gz
  a7755edc394972885c4c77a7798007e5ba4126b177c4ff6224275c4fb8f3b1c4  guix-build-68e5aafde3e8/output/riscv64-linux-gnu/SHA256SUMS.part
  b6d252993d8aae7582ad6385fe53c61c54c284c68ece6cb2b2d1ac9554e06139  guix-build-68e5aafde3e8/output/riscv64-linux-gnu/bitcoin-68e5aafde3e8-riscv64-linux-gnu-debug.tar.gz
  bb4860f3bbd815f800333124ff901d880741792ab47097f49bda3a6931144da0  guix-build-68e5aafde3e8/output/riscv64-linux-gnu/bitcoin-68e5aafde3e8-riscv64-linux-gnu.tar.gz
  3dd17deed5c5935fb28b62dfc7afca5caab0d67862cdcbf3337edae73e1d0c4c  guix-build-68e5aafde3e8/output/x86_64-apple-darwin19/SHA256SUMS.part
  fa2d68c54fda0816188c81ce2201a77340b82645da2ffe412526f92c297a82df  guix-build-68e5aafde3e8/output/x86_64-apple-darwin19/bitcoin-68e5aafde3e8-osx-unsigned.dmg
  f6e5accdcd201f522b6426e4d8cc9b3643d4d43a57d268fa0e79ea9a34cfac01  guix-build-68e5aafde3e8/output/x86_64-apple-darwin19/bitcoin-68e5aafde3e8-osx-unsigned.tar.gz
  4e5a127df957d1c73b65925d685f6620e7bc5667efcb6dcd98be76effc22fc12  guix-build-68e5aafde3e8/output/x86_64-apple-darwin19/bitcoin-68e5aafde3e8-osx64.tar.gz
  56ccd216a69acafacbdc6bae0bdcc1faa50b6a51be1aebfa7068206c88b3241a  guix-build-68e5aafde3e8/output/x86_64-linux-gnu/SHA256SUMS.part
  77b93dd5fad322636853e5b0244ffafd97cc97f3b4b4ee755d5f830b75d77d13  guix-build-68e5aafde3e8/output/x86_64-linux-gnu/bitcoin-68e5aafde3e8-x86_64-linux-gnu-debug.tar.gz
  1feda932fc127b900316a232432b91e46e57ee12a81e12a7d888fdc3296219c1  guix-build-68e5aafde3e8/output/x86_64-linux-gnu/bitcoin-68e5aafde3e8-x86_64-linux-gnu.tar.gz
  aa7c53ab4164b3736049065c3c24391fc5bd7f26b4bda4aa877c378f0636a125  guix-build-68e5aafde3e8/output/x86_64-w64-mingw32/SHA256SUMS.part
  5e76148e67aef7e91e70074bfadc08e94373449ac3b966f4343b04d230c778fd  guix-build-68e5aafde3e8/output/x86_64-w64-mingw32/bitcoin-68e5aafde3e8-win-unsigned.tar.gz
  34123e3d818beeb70113caeda66945bc7cb9d9e987515d5b149bd17b4b38da90  guix-build-68e5aafde3e8/output/x86_64-w64-mingw32/bitcoin-68e5aafde3e8-win64-debug.zip
  2bba7f40a2b23c6ea3d47c4f564ab54201bf27f7f57103a98cc9bceea4e70c4d  guix-build-68e5aafde3e8/output/x86_64-w64-mingw32/bitcoin-68e5aafde3e8-win64-setup-unsigned.exe
  0e7e124144af4a92a4344cf70a3b7c06fbd2b8782aee7ede7263893afa3a5ef0  guix-build-68e5aafde3e8/output/x86_64-w64-mingw32/bitcoin-68e5aafde3e8-win64.zip
  ```

ACKs for top commit:
  laanwj:
    Code review ACK 68e5aafde3e87c16da95410a0474f38f589afb36

Tree-SHA512: 5c25249cc178b9d54159e268390c974b739df9458d773e23c14b14d808f87f7afe314058b3c068601a9132042321973b0c9b6f81becb925665eca2738ae9a613

1 files changed, 15 insertions, 2 deletions

diff --git a/configure.ac b/configure.ac
index 507dc9399f..77f45e2133 100644
--- a/configure.ac
+++ b/configure.ac
@@ -323,6 +323,11 @@ AC_ARG_ENABLE([external-signer],
     [use_external_signer=$enableval],
     [use_external_signer=yes])
 
+AC_ARG_ENABLE([lto],
+    [AS_HELP_STRING([--enable-lto],[build using LTO (default is no)])],
+    [enable_lto=$enableval],
+    [enable_lto=no])
+
 AC_LANG_PUSH([C++])
 
 dnl Check for a flag to turn compiler warnings into errors. This is helpful for checks which may
@@ -370,6 +375,11 @@ if test "x$enable_debug" = xyes; then
   AX_CHECK_COMPILE_FLAG([-ftrapv], [DEBUG_CXXFLAGS="$DEBUG_CXXFLAGS -ftrapv"], [], [$CXXFLAG_WERROR])
 fi
 
+if test "x$enable_lto" = "xyes"; then
+  AX_CHECK_COMPILE_FLAG([-flto], [LTO_CXXFLAGS="$LTO_CXXFLAGS -flto"], [AC_MSG_ERROR([compile failed with -flto])], [$CXXFLAG_WERROR])
+  AX_CHECK_LINK_FLAG([-flto], [LTO_LDFLAGS="$LTO_LDFLAGS -flto"], [AC_MSG_ERROR([link failed with -flto])], [$CXXFLAG_WERROR])
+fi
+
 if test x$use_sanitizers != x; then
   dnl First check if the compiler accepts flags. If an incompatible pair like
   dnl -fsanitize=address,thread is used here, this check will fail. This will also
@@ -1823,6 +1833,8 @@ AC_SUBST(GPROF_LDFLAGS)
 AC_SUBST(HARDENED_CXXFLAGS)
 AC_SUBST(HARDENED_CPPFLAGS)
 AC_SUBST(HARDENED_LDFLAGS)
+AC_SUBST(LTO_CXXFLAGS)
+AC_SUBST(LTO_LDFLAGS)
 AC_SUBST(PIC_FLAGS)
 AC_SUBST(PIE_FLAGS)
 AC_SUBST(SANITIZER_CXXFLAGS)
@@ -1938,6 +1950,7 @@ echo "  sanitizers      = $use_sanitizers"
 echo "  debug enabled   = $enable_debug"
 echo "  gprof enabled   = $enable_gprof"
 echo "  werror          = $enable_werror"
+echo "  LTO             = $enable_lto"
 echo
 echo "  target os       = $TARGET_OS"
 echo "  build os        = $build_os"
@@ -1946,7 +1959,7 @@ echo "  CC              = $CC"
 echo "  CFLAGS          = $PTHREAD_CFLAGS $CFLAGS"
 echo "  CPPFLAGS        = $DEBUG_CPPFLAGS $HARDENED_CPPFLAGS $CPPFLAGS"
 echo "  CXX             = $CXX"
-echo "  CXXFLAGS        = $DEBUG_CXXFLAGS $HARDENED_CXXFLAGS $WARN_CXXFLAGS $NOWARN_CXXFLAGS $ERROR_CXXFLAGS $GPROF_CXXFLAGS $CXXFLAGS"
-echo "  LDFLAGS         = $PTHREAD_LIBS $HARDENED_LDFLAGS $GPROF_LDFLAGS $LDFLAGS"
+echo "  CXXFLAGS        = $LTO_CXXFLAGS $DEBUG_CXXFLAGS $HARDENED_CXXFLAGS $WARN_CXXFLAGS $NOWARN_CXXFLAGS $ERROR_CXXFLAGS $GPROF_CXXFLAGS $CXXFLAGS"
+echo "  LDFLAGS         = $LTO_LDFLAGS $PTHREAD_LIBS $HARDENED_LDFLAGS $GPROF_LDFLAGS $LDFLAGS"
 echo "  ARFLAGS         = $ARFLAGS"
 echo