Detect GHC 9.4 and use -fprof-late

ChangeLog.md

@@ -10,6 +10,12 @@ Major changes:
 
 Behavior changes:
 
+* From GHC 9.4.1, the strategy for the automatic insertion of cost-centres for
+  profiling recommended by the GHC User's Guide is `-fprof-late`. Stack's
+  `build --profile` command now adopts that recommendation (rather than
+  `-fprof-auto`, still applicable to earlier GHC versions). Existing profiling
+  builds will be rebuilt.
+
 Other enhancements:
 
 * Consider Cabal 3.18 to be a tested library and remove warnings.

doc/commands/build_command.md

@@ -979,20 +979,24 @@ expressions, and generate a profiling report in tests or benchmarks.
 
 GHC provides various strategies for the automatic insertion of cost-centres into
 the compiled program. The flag enables the strategy recommended in the GHC
-User's Guide (GHC flag `-fprof-auto`) and gives every Constant Applicative Form
-(CAF, a top-level thunk) its own cost-centre stack) (GHC flag `-fprof-cafs`).
+User's Guide and gives every Constant Applicative Form (CAF, a top-level thunk)
+its own cost-centre stack) (GHC flag `-fprof-cafs`).
 
-!!! note
+The recommended strategy:
 
-    From GHC 9.4.1, the stategy recommended in the GHC User's Guide has been
-    `-fprof-late`. Stack has not yet been updated to reflect that.
+* **for GHC 9.4.1 and later**, is enabled by GHC flag `-fprof-late`. This
+  strategy annotates, after GHC's optimizer has run and unfoldings have been
+  created, all top-level bindings (only) with `SCC` (Set Cost Centre). If a
+  function is inlined into a use site its costs will be counted against the
+  caller’s cost-centre; and
 
-The recommended strategy annotates, before GHC's optimizer has run, all bindings (top-level or nested, whether exported or not), other than those marked
-`INLINE`, with `SCC` (Set Cost Centre).
+* **otherwise**, is enabled by GHC flag `-fprof-auto`. This strategy annotates,
+  before GHC's optimizer has run, all bindings (top-level or nested, whether
+  exported or not), other than those marked `INLINE`, with `SCC`.
 
-The GHC flags set by the flag can be reversed with GHC flags `-fno-prof-auto` or
-`-fno-prof-cafs` and other GHC flags applied. See the
-[`--ghc-options`](#-ghc-options-option) option.
+The GHC flags set by the flag can be reversed with GHC flags `-fno-prof-late` or
+`-fno-prof-auto` (as applicable) or `-fno-prof-cafs` and other GHC flags
+applied. See the [`--ghc-options`](#-ghc-options-option) option.
 
 The flag affects the location of the local project installation directory. See
 the [`stack path --local-install-root`](path_command.md) command.

src/Stack/Build/Source.hs

@@ -113,7 +113,6 @@ loadSourceMap targets boptsCli sma = do
   bconfig <- view buildConfigL
   let errsPackages = mapMaybe checkPackage packagesWithCliFlags
       compiler = sma.compiler
-      ghcVersion = getGhcVersion compiler
       buildOpts = bconfig.config.build
       infoTableProfSupported = ghcVersion >= mkVersion [9, 2, 1]
       infoTableProfUnsupportedWarning =
@@ -146,6 +145,7 @@ loadSourceMap targets boptsCli sma = do
     , globalPkgs
     }
  where
+  ghcVersion = getGhcVersion sma.compiler
   cliFlags = boptsCli.flags
   targetsAndSmaDeps = targets.deps <> sma.deps
   packagesWithCliFlags = mapMaybe maybeProjectWithCliFlags $ Map.toList cliFlags
@@ -212,6 +212,7 @@ loadSourceMap targets boptsCli sma = do
             ghcOptions = generalGhcOptions
               bconfig
               boptsCli
+              ghcVersion
               isTarget
               isProjectPackage
               isInfoTableProf
@@ -276,7 +277,7 @@ hashSourceMapData boptsCli sm = do
       isInfoTableProf =
         ghcVersion >= mkVersion [9, 2, 1] && bc.config.build.infoTableProf
       bootGhcOpts =
-        map display (generalGhcOptions bc boptsCli False False isInfoTableProf)
+        map display (generalGhcOptions bc boptsCli ghcVersion False False isInfoTableProf)
       hashedContent =
            toLazyByteString $ compilerPath
         <> compilerInfo
@@ -337,11 +338,12 @@ generalCabalConfigOpts bconfig boptsCli name isTarget isLocal = concat
 generalGhcOptions ::
      BuildConfig
   -> BuildOptsCLI
+  -> Version
   -> Bool
   -> Bool
   -> Bool
   -> [Text]
-generalGhcOptions bconfig boptsCli isTarget isLocal isInfoTableProf = concat
+generalGhcOptions bconfig boptsCli ghcVersion isTarget isLocal isInfoTableProf = concat
   [ Map.findWithDefault [] AGOEverything config.ghcOptionsByCat
   , if isLocal
       then Map.findWithDefault [] AGOLocals config.ghcOptionsByCat
@@ -351,7 +353,7 @@ generalGhcOptions bconfig boptsCli isTarget isLocal isInfoTableProf = concat
       else []
   , concat [["-fhpc"] | isLocal && bopts.testOpts.coverage]
   , if bopts.libProfile || bopts.exeProfile
-      then ["-fprof-auto", "-fprof-cafs"]
+      then [recommendedProfStrategy, "-fprof-cafs"]
       else []
   , [ "-g" | not $ bopts.libStrip || bopts.exeStrip ]
   , if isInfoTableProf
@@ -364,6 +366,12 @@ generalGhcOptions bconfig boptsCli isTarget isLocal isInfoTableProf = concat
  where
   bopts =  config.build
   config = view configL bconfig
+  -- The strategy for the automatic insertion of cost centres for profiling, as
+  -- recommended by the GHC User's Guide:
+  recommendedProfStrategy :: Text
+  recommendedProfStrategy
+    | ghcVersion >= mkVersion [9, 4, 1] = "-fprof-late"
+    | otherwise = "-fprof-auto"
   includeExtraOptions =
     case config.applyGhcOptions of
       AGOTargets -> isTarget

src/Stack/ConfigureOpts.hs

@@ -127,6 +127,12 @@ configureOptsNonPathRelated econfig bco deps isLocal package = concat
     | bopts.libProfile || bopts.exeProfile
     ]
   , ["--enable-profiling" | bopts.exeProfile && isLocal]
+    -- The default --profiling-detail is exported-functions (equivalent to GHC's
+    -- -fprof-auto-exported) and toplevel-functions (equivalent to GHC's
+    -- -fprof-auto-top). Neither adds anything to GHC's -fprof-auto and neither
+    -- are required for GHC's -fprof-late. So, we turn it off, which applies to
+    -- both executables and libraries:
+  , ["--profiling-detail=none"]
   , ["--enable-split-objs" | bopts.splitObjs]
   , [ "--disable-library-stripping"
     | not $ bopts.libStrip || bopts.exeStrip