Remove dynamic-by-default (#16782)

Dynamic-by-default was a mechanism to automatically select the -dynamic
way for some targets.

It was implemented in a convoluted way: it was defined as a flavour
option, hence it couldn't be passed as a global settings (which are
produced by `configure` before considering flavours), so a build system
rule was used to pass -DDYNAMIC_BY_DEFAULT to the C compiler so that
deriveConstants could infer it.

* Make build system has it disabled for 8 years (951e28c0625ece7e0db6ac9d4a1e61e2737b10de)
* It has never been implemented in Hadrian
* Last time someone tried to enable it 1 year ago it didn't work (!2436)
* Having this as a global constant impedes making GHC multi-target (see !5427)

This commit fully removes support for dynamic-by-default. If someone
wants to reimplement something like this, it would probably need to move
the logic in the compiler.

(Doing this would probably need some refactoring of the way the compiler
handles DynFlags: DynFlags are used to store and to pass enabled ways to
many parts of the compiler. It can be set by command-line flags, GHC
API, global settings. In multi-target GHC, we will use DynFlags to load
the target platform and its constants: but at this point with the
current DynFlags implementation we can't easily update the existing
DynFlags with target-specific options such as dynamic-by-default without
overriding ways previously set by the user.)

3 files changed, 0 insertions, 5 deletions

diff --git a/hadrian/src/Oracles/TestSettings.hs b/hadrian/src/Oracles/TestSettings.hs
index ba89e00beb..b5f197299b 100644
--- a/hadrian/src/Oracles/TestSettings.hs
+++ b/hadrian/src/Oracles/TestSettings.hs
@@ -28,7 +28,6 @@ data TestSetting = TestHostOS
                  | TestGhcWithInterpreter
                  | TestGhcUnregisterised
                  | TestGhcWithSMP
-                 | TestGhcDynamicByDefault
                  | TestGhcDynamic
                  | TestGhcProfiled
                  | TestAR
@@ -57,7 +56,6 @@ testSetting key = do
         TestGhcWithInterpreter    -> "GhcWithInterpreter"
         TestGhcUnregisterised     -> "GhcUnregisterised"
         TestGhcWithSMP            -> "GhcWithSMP"
-        TestGhcDynamicByDefault   -> "GhcDynamicByDefault"
         TestGhcDynamic            -> "GhcDynamic"
         TestGhcProfiled           -> "GhcProfiled"
         TestAR                    -> "AR"
diff --git a/hadrian/src/Settings/Builders/DeriveConstants.hs b/hadrian/src/Settings/Builders/DeriveConstants.hs
index be115fb789..856e85aac0 100644
--- a/hadrian/src/Settings/Builders/DeriveConstants.hs
+++ b/hadrian/src/Settings/Builders/DeriveConstants.hs
@@ -11,7 +11,6 @@ deriveConstantsPairs =
   , ("platformConstants", "--gen-haskell-value")
   ]
 
--- TODO: do we need to support `includes_CC_OPTS += -DDYNAMIC_BY_DEFAULT`?
 deriveConstantsBuilderArgs :: Args
 deriveConstantsBuilderArgs = builder DeriveConstants ? do
     cFlags <- includeCcArgs
diff --git a/hadrian/src/Settings/Builders/RunTest.hs b/hadrian/src/Settings/Builders/RunTest.hs
index 8fcc0aaee2..7ea8d4f364 100644
--- a/hadrian/src/Settings/Builders/RunTest.hs
+++ b/hadrian/src/Settings/Builders/RunTest.hs
@@ -63,7 +63,6 @@ runTestBuilderArgs = builder RunTest ? do
     let hasRtsWay w = elem w rtsWays
         hasLibWay w = elem w libWays
     hasDynamic          <- getBooleanSetting TestGhcDynamic
-    hasDynamicByDefault <- getBooleanSetting TestGhcDynamicByDefault
     withNativeCodeGen   <- getBooleanSetting TestGhcWithNativeCodeGen
     withInterpreter     <- getBooleanSetting TestGhcWithInterpreter
     unregisterised      <- getBooleanSetting TestGhcUnregisterised
@@ -127,7 +126,6 @@ runTestBuilderArgs = builder RunTest ? do
             , arg "-e", arg $ asBool "config.have_fast_bignum=" (bignumBackend /= "native" && not bignumCheck)
             , arg "-e", arg $ asBool "ghc_with_smp=" withSMP
 
-            , arg "-e", arg $ "config.ghc_dynamic_by_default=" ++ show hasDynamicByDefault
             , arg "-e", arg $ "config.ghc_dynamic=" ++ show hasDynamic
 
             , arg "-e", arg $ "config.wordsize=" ++ show wordsize