Disable optimisation when building Cabal in development flavours

This updates the make and Hadrian build flavours targetting developers
to disable optimisation when building the Cabal library. Cabal tends to
tickle some very bad compiler performance cases (e.g. #16577) so
disabling optimisation here makes a sizeable impact on overall build
time.

See #16817.

5 files changed, 20 insertions, 3 deletions

diff --git a/hadrian/cabal.project b/hadrian/cabal.project
index d9c329141f..0df6b15695 100644
--- a/hadrian/cabal.project
+++ b/hadrian/cabal.project
@@ -1,8 +1,8 @@
 packages: ./
           ../libraries/Cabal/Cabal/
 
-# N.B. Compile with -O0 since this is not a performance-critical executable
-# and the Cabal takes nearly twice as long to build with -O1. See #16817.
+-- N.B. Compile with -O0 since this is not a performance-critical executable
+-- and the Cabal takes nearly twice as long to build with -O1. See #16817.
 package Cabal
   optimization: False
 
diff --git a/hadrian/src/Settings/Flavours/Development.hs b/hadrian/src/Settings/Flavours/Development.hs
index 5fcc88be1e..08200dfa5a 100644
--- a/hadrian/src/Settings/Flavours/Development.hs
+++ b/hadrian/src/Settings/Flavours/Development.hs
@@ -2,6 +2,7 @@ module Settings.Flavours.Development (developmentFlavour) where
 
 import Expression
 import Flavour
+import Packages
 import {-# SOURCE #-} Settings.Default
 
 -- Please update doc/flavours.md when changing this file.
@@ -17,7 +18,10 @@ developmentArgs :: Stage -> Args
 developmentArgs ghcStage = do
     stage <- getStage
     sourceArgs SourceArgs
-        { hsDefault  = pure ["-O", "-H64m"]
+        { hsDefault  = mconcat [ pure ["-O", "-H64m"],
+                                 -- Disable optimization when building Cabal;
+                                 -- this saves many minutes of build time.
+                                 package cabal ? pure ["-O0"]]
         , hsLibrary  = notStage0 ? arg "-dcore-lint"
         , hsCompiler = mconcat [stage0 ? arg "-O2",
                                 succ stage == ghcStage ? pure ["-O0", "-DDEBUG"]]
diff --git a/mk/flavours/devel1.mk b/mk/flavours/devel1.mk
index e062a57909..1c03aff10b 100644
--- a/mk/flavours/devel1.mk
+++ b/mk/flavours/devel1.mk
@@ -10,3 +10,7 @@ BUILD_SPHINX_PDF   = NO
 BUILD_MAN          = NO
 
 LAX_DEPENDENCIES   = YES
+
+# Reduce optimisation when building Cabal; this makes a significant difference
+# in overall build time. See #16817.
+libraries/Cabal_dist-install_HC_OPTS += -O0
diff --git a/mk/flavours/devel2.mk b/mk/flavours/devel2.mk
index 1c8e24f745..2d7d3b3884 100644
--- a/mk/flavours/devel2.mk
+++ b/mk/flavours/devel2.mk
@@ -10,3 +10,7 @@ BUILD_SPHINX_PDF   = NO
 BUILD_MAN          = NO
 
 LAX_DEPENDENCIES   = YES
+
+# Reduce optimisation when building Cabal; this makes a significant difference
+# in overall build time. See #16817.
+libraries/Cabal_dist-install_HC_OPTS += -O0
diff --git a/mk/flavours/validate.mk b/mk/flavours/validate.mk
index 3fd916afb0..6395d2d62f 100644
--- a/mk/flavours/validate.mk
+++ b/mk/flavours/validate.mk
@@ -27,6 +27,10 @@ endif
 
 WERROR             = -Werror
 
+# Reduce optimisation when building Cabal; this makes a significant difference
+# in overall build time. See #16817.
+libraries/Cabal_dist-install_HC_OPTS += -O0
+
 # DO NOT EDIT THIS FILE! Instead, create a file mk/validate.mk, whose settings
 # will override these. See also mk/custom-settings.mk.
 #
@@ -36,6 +40,7 @@ WERROR             = -Werror
 #
 #
 # Note [validate build settings]
+# ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 #
 # Using GhcStage2HcOpts=-O (rather than -O0) here bringes my validate down from
 # 22mins to 16 mins. Compiling stage2 takes longer, but we gain a faster