autoconf: Sane --enable-debug defaults. #16435

1. 
   dongcarl commented at 3:14 pm on July 22, 2019: member

   0Don't optimize even if variables adhere to as-if rule. This is a
   1somewhat sane default for debugging.
   

   ---

   Fixes: #14830

   This is more of a “do something dumb and have people correct you” kind of PR. The end goal is to have a configure flag that will allow for debugging without annoying “optimized out” messages, for developer experiences’ sake. This is the minimal diff, but people have suggested --enable-debug-slow in the past.

2. dongcarl added the label Build system on Jul 22, 2019
3. 
   jonasschnelli commented at 3:21 pm on July 22, 2019: contributor

   Yes. Please! On macOS, without that fix, debugging with lldb/gdb is impossible. Concept ACK
4. in configure.ac:274 in e85368fb89 outdated

   270@@ -271,11 +271,11 @@ if test "x$enable_debug" = xyes; then
   271   if test "x$CXXFLAGS_overridden" = xno; then
   272 	CXXFLAGS=""
   273   fi
   274-  # Prefer -Og, fall back to -O0 if that is unavailable.
   275+  # Prefer -O0, fall back to -Og if that is unavailable.
   

   ---

   ---

   

   laanwj commented at 4:58 pm on July 22, 2019:

   I think it’s fine to add -O0 unconditionally. E.g.: I would be very surprised if a compiler supports -Og but not -O0,
5. 
   achow101 commented at 5:21 pm on July 22, 2019: member

   Concept ACK.

   One thing to note is that on Clang 8, I get a bunch of compiler warnings about things needing optimization if -O0 is set.

6. 
   laanwj commented at 6:10 pm on July 22, 2019: member

   BTW: this effectively reverts 9e49db2426cd4508d9dd95c7461e107bab7fd7de (#13005)
7. autoconf: Sane --enable-debug defaults.

   Don't optimize at all when --enable-debug is supplied. This makes sure
   that nothing is optimized out.

   d6ac25bdd9
8. dongcarl force-pushed on Jul 30, 2019
9. 
   dongcarl commented at 8:00 pm on July 30, 2019: member

   Addressed comments, there was some discussion on this here: http://gnusha.org/bitcoin-builds/2019-07-30.log
10. 
    theuni commented at 3:00 pm on July 31, 2019: member

    From the above discussion: -0 from me.

    I would expect –enable-debug to turn on Og:

    -Og Optimize debugging experience. -Og enables optimizations that do not interfere with debugging. It should be the optimization level of choice for the standard edit-compile-debug cycle, offering a reasonable level of optimization while maintaining fast compilation and a good debugging experience.

    But I don’t care that much, and the people that do care seem to want –enable-debug to mean more than the “standard edit-compile-debug cycle”. That seems reasonable enough, so sure.

11. dongcarl marked this as ready for review on Jul 31, 2019
12. 
    jonasschnelli commented at 8:11 am on August 8, 2019: contributor

    Tested ACK d6ac25bdd96589a71006e3ab3f303b091ffaa9e4 Brings back debugability on macOS 10.14 with clang version Apple LLVM version 10.0.1 (clang-1001.0.46.4).
13. MarcoFalke added this to the milestone 0.19.0 on Aug 8, 2019
14. jonasschnelli merged this on Aug 14, 2019
15. jonasschnelli closed this on Aug 14, 2019

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Contributors
dongcarl jonasschnelli laanwj achow101 theuni

Labels
Build system

Milestone
0.19.0