gambit: set CC to full path, fixes #78921

Use -Os rather than -O2 as our compilation flag, document why.

Document why we always use gcc over clang.

Fix openssl path in gambit.
Stop trying to make static openssl.

pkgs/development/compilers/gambit/bootstrap.nix

@@ -1,4 +1,4 @@
-{ stdenv, fetchurl, autoconf, ... }:
+{ stdenv, fetchurl, autoconf, gcc, coreutils, ... }:
 
 stdenv.mkDerivation {
   pname = "gambit-bootstrap";
@@ -12,6 +12,10 @@ stdenv.mkDerivation {
   buildInputs = [ autoconf ];
 
   configurePhase = ''
+    export CC=${gcc}/bin/gcc CXX=${gcc}/bin/g++ \
+           CPP=${gcc}/bin/cpp CXXCPP=${gcc}/bin/cpp LD=${gcc}/bin/ld \
+           XMKMF=${coreutils}/bin/false
+    unset CFLAGS LDFLAGS LIBS CPPFLAGS CXXFLAGS
     ./configure --prefix=$out
   '';
 

pkgs/development/compilers/gambit/build.nix

@@ -1,4 +1,19 @@
-{ stdenv, git, openssl, autoconf, pkgs, makeStaticLibraries, version, src }:
+{ stdenv, git, openssl, autoconf, pkgs, makeStaticLibraries, version, gcc, src, coreutils }:
+
+# Note that according to a benchmark run by Marc Feeley on May 2018,
+# clang is 10x (with default settings) to 15% (with -O2) slower than GCC at compiling
+# Gambit output, producing code that is 3x slower. IIRC the benchmarks from Gambit@30,
+# the numbers were still heavily in favor of GCC in October 2019.
+# Thus we use GCC over clang, even on macOS.
+
+# Also note that I (fare) just ran benchmarks from https://github.com/ecraven/r7rs-benchmarks
+# with Gambit 4.9.3 with -O1 vs -O2 vs -Os on Feb 2020. Which wins depends on the benchmark.
+# The fight is unclear between -O1 and -O2, where -O1 wins more often, by up to 17%,
+# but sometimes -O2 wins, once by up to 43%, so that overall -O2 is 5% faster.
+# However, -Os seems more consistent in winning slightly against both -O1 and -O2,
+# and is overall 15% faster than -O2. As for compile times, -O1 is fastest,
+# -Os is about 29%-33% slower than -O1, while -O2 is about 40%-50% slower than -O1.
+# Overall, -Os seems like the best choice, and that's what we now use.
 
 stdenv.mkDerivation rec {
   pname = "gambit";
@@ -7,38 +22,48 @@ stdenv.mkDerivation rec {
 
   bootstrap = import ./bootstrap.nix ( pkgs );
 
-  # Use makeStaticLibraries to enable creation of statically linked binaries
-  buildInputs = [ git autoconf bootstrap openssl (makeStaticLibraries openssl)];
+  # TODO: if/when we can get all the library packages we depend on to have static versions,
+  # we could use something like (makeStaticLibraries openssl) to enable creation
+  # of statically linked binaries by gsc.
+  buildInputs = [ git autoconf bootstrap openssl ];
+
+  configureFlags = [
+    "--enable-single-host"
+    "--enable-c-opt=-Os"
+    "--enable-gcc-opts"
+    "--enable-shared"
+    "--enable-absolute-shared-libs" # Yes, NixOS will want an absolute path, and fix it.
+    "--enable-poll"
+    "--enable-openssl"
+    "--enable-default-runtime-options=f8,-8,t8" # Default to UTF-8 for source and all I/O
+    # "--enable-debug" # Nope: enables plenty of good stuff, but also the costly console.log
+    # "--enable-multiple-versions" # Nope, NixOS already does version multiplexing
+    # "--enable-guide"
+    # "--enable-track-scheme"
+    # "--enable-high-res-timing"
+    # "--enable-max-processors=4"
+    # "--enable-multiple-vms"
+    # "--enable-dynamic-tls"
+    # "--enable-multiple-threaded-vms"  # when SMP branch is merged in
+    # "--enable-thread-system=posix"    # default when --enable-multiple-vms is on.
+    # "--enable-profile"
+    # "--enable-coverage"
+    # "--enable-inline-jumps"
+    # "--enable-char-size=1" # default is 4
+  ];
 
   configurePhase = ''
-    options=(
-      --prefix=$out
-      --enable-single-host
-      --enable-c-opt=-O2
-      --enable-gcc-opts
-      --enable-shared
-      --enable-absolute-shared-libs # Yes, NixOS will want an absolute path, and fix it.
-      --enable-poll
-      --enable-openssl
-      --enable-default-runtime-options="f8,-8,t8" # Default to UTF-8 for source and all I/O
-      #--enable-debug # Nope: enables plenty of good stuff, but also the costly console.log
+    export CC=${gcc}/bin/gcc CXX=${gcc}/bin/g++ \
+           CPP=${gcc}/bin/cpp CXXCPP=${gcc}/bin/cpp LD=${gcc}/bin/ld \
+           XMKMF=${coreutils}/bin/false
+    unset CFLAGS LDFLAGS LIBS CPPFLAGS CXXFLAGS
+    ./configure --prefix=$out ${builtins.concatStringsSep " " configureFlags}
 
-      #--enable-multiple-versions # Nope, NixOS already does version multiplexing
-      #--enable-guide
-      #--enable-track-scheme
-      #--enable-high-res-timing
-      #--enable-max-processors=4
-      #--enable-multiple-vms
-      #--enable-dynamic-tls
-      #--enable-multiple-vms
-      #--enable-multiple-threaded-vms  ## when SMP branch is merged in
-      #--enable-thread-system=posix    ## default when --enable-multiple-vms is on.
-      #--enable-profile
-      #--enable-coverage
-      #--enable-inline-jumps
-      #--enable-char-size=1" ; default is 4
-    )
-    ./configure ''${options[@]}
+    # OS-specific paths are hardcoded in ./configure
+    substituteInPlace config.status \
+      --replace /usr/local/opt/openssl/lib "${openssl.out}/lib" \
+      --replace /usr/local/opt/openssl@1.1/lib "${openssl.out}/lib"
+    ./config.status
   '';
 
   buildPhase = ''