Hadrian: fix ghcDebugAssertions off-by-one error

Commit 6b2f7ffe changed the logic that decided whether to enable debug
assertions. However, it had an off-by-one error, as the stage parameter
to the function inconsistently referred to the stage of the compiler
being used to build or the stage of the compiler we are building.

This patch makes it consistent. Now the parameter always refers to the
the compiler which is being built.

In particular, this patch re-enables
assertions in the stage 2 compiler when building with devel2 flavour,
and disables assertions in the stage 2 compiler when building with
validate flavour.

Some extra performance tests are now run in the "validate" jobs because
the stage2 compiler no longer contains assertions.

-------------------------
Metric Decrease:
    CoOpt_Singletons
    MultiComponentModules
    MultiComponentModulesRecomp
    MultiLayerModulesTH_OneShot
    T11374
    T12227
    T12234
    T13253-spj
    T13701
    T14683
    T14697
    T15703
    T17096
    T17516
    T18304
    T18478
    T18923
    T5030
    T9872b
    TcPlugin_RewritePerf
Metric Increase:
    MultiComponentModules
    MultiComponentModulesRecomp
    MultiLayerModules
    MultiLayerModulesRecomp
    MultiLayerModulesTH_Make
    T13386
    T13719
    T3294
    T9233
    T9675
    parsing001
-------------------------

5 files changed, 33 insertions, 21 deletions

diff --git a/hadrian/doc/user-settings.md b/hadrian/doc/user-settings.md
index 6e98d8a02a..795f877557 100644
--- a/hadrian/doc/user-settings.md
+++ b/hadrian/doc/user-settings.md
@@ -25,7 +25,7 @@ data Flavour = Flavour {
     packages :: Stage -> Action [Package],
     -- | Bignum backend: 'native', 'gmp', 'ffi', etc.
     bignumBackend :: String,
-    -- | Check bignum backend against native
+    -- | Check selected bignum backend against native backend
     bignumCheck :: Bool,
     -- | Build libraries these ways.
     libraryWays :: Ways,
@@ -34,15 +34,20 @@ data Flavour = Flavour {
     -- | Build dynamic GHC programs.
     dynamicGhcPrograms :: Action Bool,
     -- | Enable GHCi debugger.
-    ghciWithDebugger :: Bool,
+    ghciWithDebugger :: Stage -- ^ stage of the /built/ compiler
+                     -> Bool,
     -- | Build profiled GHC.
-    ghcProfiled :: Bool,
+    ghcProfiled :: Stage -- ^ stage of the /built/ compiler
+                -> Bool,
     -- | Build GHC with the debug RTS.
-    ghcDebugged :: Bool,
+    ghcDebugged :: Stage -- ^ stage of the /built/ compiler
+                -> Bool,
     -- | Build GHC with debug assertions (-DDEBUG).
-    ghcDebugAssertions :: Bool,
+    ghcDebugAssertions :: Stage -- ^ stage of the /built/ compiler
+                       -> Bool,
     -- | Build the GHC executable against the threaded runtime system.
-    ghcThreaded :: Bool,
+    ghcThreaded :: Stage -- ^ stage of the /built/ compiler
+                -> Bool,
     -- | Whether to build docs and which ones
     --   (haddocks, user manual, haddock manual)
     ghcDocs :: Action DocTargets }
diff --git a/hadrian/src/Flavour/Type.hs b/hadrian/src/Flavour/Type.hs
index 7718d63d7f..60021268fa 100644
--- a/hadrian/src/Flavour/Type.hs
+++ b/hadrian/src/Flavour/Type.hs
@@ -18,9 +18,9 @@ data Flavour = Flavour {
     args :: Args,
     -- | Build these packages.
     packages :: Stage -> Action [Package],
-    -- | 'native', 'gmp', 'ffi'.
+    -- | Bignum backend: 'native', 'gmp', 'ffi', etc.
     bignumBackend :: String,
-    -- | Check selected backend against native backend
+    -- | Check selected bignum backend against native backend
     bignumCheck :: Bool,
     -- | Build libraries these ways.
     libraryWays :: Ways,
@@ -29,15 +29,20 @@ data Flavour = Flavour {
     -- | Build dynamic GHC programs.
     dynamicGhcPrograms :: Action Bool,
     -- | Enable GHCi debugger.
-    ghciWithDebugger :: Stage -> Bool,
+    ghciWithDebugger :: Stage -- ^ stage of the /built/ compiler
+                     -> Bool,
     -- | Build profiled GHC.
-    ghcProfiled :: Stage -> Bool,
+    ghcProfiled :: Stage -- ^ stage of the /built/ compiler
+                -> Bool,
     -- | Build GHC with the debug RTS.
-    ghcDebugged :: Stage -> Bool,
-    -- | Build GHC with debug assertions.
-    ghcDebugAssertions :: Stage -> Bool,
+    ghcDebugged :: Stage -- ^ stage of the /built/ compiler
+                -> Bool,
+    -- | Build GHC with debug assertions (-DDEBUG).
+    ghcDebugAssertions :: Stage -- ^ stage of the /built/ compiler
+                       -> Bool,
     -- | Build the GHC executable against the threaded runtime system.
-    ghcThreaded :: Stage -> Bool,
+    ghcThreaded :: Stage -- ^ stage of the /built/ compiler
+                -> Bool,
     -- | Whether to build docs and which ones
     --   (haddocks, user manual, haddock manual)
     ghcDocs :: Action DocTargets }
diff --git a/hadrian/src/Settings/Builders/RunTest.hs b/hadrian/src/Settings/Builders/RunTest.hs
index e7935a3a33..f450a13f91 100644
--- a/hadrian/src/Settings/Builders/RunTest.hs
+++ b/hadrian/src/Settings/Builders/RunTest.hs
@@ -101,7 +101,7 @@ inTreeCompilerArgs stg = do
     unregisterised      <- flag GhcUnregisterised
     tables_next_to_code <- flag TablesNextToCode
     withSMP             <- targetSupportsSMP
-    debugAssertions     <- ($ stg) . ghcDebugAssertions <$> flavour
+    debugAssertions     <- ($ succStage stg) . ghcDebugAssertions <$> flavour
     profiled            <- ghcProfiled        <$> flavour <*> pure stg
 
     os          <- setting HostOs
diff --git a/hadrian/src/Settings/Flavours/Development.hs b/hadrian/src/Settings/Flavours/Development.hs
index 715532e08a..ccc592cdc6 100644
--- a/hadrian/src/Settings/Flavours/Development.hs
+++ b/hadrian/src/Settings/Flavours/Development.hs
@@ -16,12 +16,12 @@ developmentFlavour ghcStage = defaultFlavour
     , libraryWays = pure $ Set.fromList [vanilla]
     , rtsWays = Set.fromList <$> mconcat [pure [vanilla, debug], targetSupportsThreadedRts ? pure [threaded, threadedDebug]]
     , dynamicGhcPrograms = return False
-    , ghcDebugAssertions = (>= Stage2) }
+    , ghcDebugAssertions = (== ghcStage) }
     where
       stageString Stage2 = "2"
       stageString Stage1 = "1"
       stageString Stage3 = "3"
-      stageString s = error ("developmentFlavour not support for " ++ show s)
+      stageString s = error ("developmentFlavour not supported for " ++ show s)
 
 developmentArgs :: Stage -> Args
 developmentArgs ghcStage = do
diff --git a/hadrian/src/Settings/Packages.hs b/hadrian/src/Settings/Packages.hs
index e99e639eb8..587dae16e8 100644
--- a/hadrian/src/Settings/Packages.hs
+++ b/hadrian/src/Settings/Packages.hs
@@ -13,7 +13,6 @@ packageArgs :: Args
 packageArgs = do
     stage        <- getStage
     path         <- getBuildPath
-    root         <- getBuildRoot
     compilerPath <- expr $ buildPath (vanillaContext stage compiler)
 
     let -- Do not bind the result to a Boolean: this forces the configure rule
@@ -29,7 +28,10 @@ packageArgs = do
     cursesLibraryDir <- getSetting CursesLibDir
     ffiIncludeDir  <- getSetting FfiIncludeDir
     ffiLibraryDir  <- getSetting FfiLibDir
-    debugAssertions  <- ghcDebugAssertions <$> expr flavour
+    debugAssertions  <- ( `ghcDebugAssertions` (succStage stage) ) <$> expr flavour
+      -- NB: in this function, "stage" is the stage of the compiler we are
+      -- using to build, but ghcDebugAssertions wants the stage of the compiler
+      -- we are building, which we get using succStage.
 
     mconcat
         --------------------------------- base ---------------------------------
@@ -52,7 +54,7 @@ packageArgs = do
           [ builder Alex ? arg "--latin1"
 
           , builder (Ghc CompileHs) ? mconcat
-            [ debugAssertions stage ?  arg "-DDEBUG"
+            [ debugAssertions ? arg "-DDEBUG"
 
             , inputs ["**/GHC.hs", "**/GHC/Driver/Make.hs"] ? arg "-fprof-auto"
             , input "**/Parser.hs" ?
@@ -83,7 +85,7 @@ packageArgs = do
         , package ghc ? mconcat
           [ builder Ghc ? mconcat
              [ arg ("-I" ++ compilerPath)
-             , debugAssertions stage ? arg "-DDEBUG" ]
+             , debugAssertions ? arg "-DDEBUG" ]
 
           , builder (Cabal Flags) ? mconcat
             [ andM [expr ghcWithInterpreter, notStage0] `cabalFlag` "internal-interpreter"