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Cheng Shao pushed to branch wip/fix-use-std-ap-thunk at Glasgow Haskell Compiler / GHC

Commits:

d5444d78

by Cheng Shao at 2026-07-14T11:18:52+00:00

compiler: fix redundant AP thunk codegen when not using -ticky-ap-thunk

This patch fixes a double negation confusion in !7525 that results in
some redundant AP thunk code generation when not using
-ticky-ap-thunk. Now, we use `stgToCmmUseStdApThunk` to indicate
whether precomputed AP thunks in the RTS should be used, which
defaults to `True`, unless `-ticky-ap-thunk` is passed.
`-finfo-table-map` now also implies `-ticky-ap-thunk`, since when
doing IPE profiling we want the generated AP thunks to be unique.
Fixes #27502.

-------------------------
Metric Decrease:
    T3064
-------------------------

Co-authored-by: Codex <codex@openai.com>

5 changed files:

+ changelog.d/fix-use-std-ap-thunk
compiler/GHC/Driver/Config/StgToCmm.hs
compiler/GHC/Driver/Flags.hs
compiler/GHC/StgToCmm/Bind.hs
compiler/GHC/StgToCmm/Config.hs

Changes:

changelog.d/fix-use-std-ap-thunk

 +section: codegen
 +synopsis: Fix redundant AP thunk codegen when not using -ticky-ap-thunk
 +issues: #27502
 +mrs: !16340

compiler/GHC/Driver/Config/StgToCmm.hs

@@ -87,7 +87,7 @@ initStgToCmmConfig dflags mod = StgToCmmConfig
    , stgToCmmAvx           = isAvxEnabled                   dflags
    , stgToCmmAvx2          = isAvx2Enabled                  dflags
    , stgToCmmAvx512f       = isAvx512fEnabled               dflags
 -  , stgToCmmTickyAP       = gopt Opt_Ticky_AP dflags
 +  , stgToCmmUseStdApThunk = not $ gopt Opt_Ticky_AP dflags
    -- See Note [Saving foreign call target to local]
    , stgToCmmSaveFCallTargetToLocal = any (callerSaves platform) $ activeStgRegs platform
    } where profile  = targetProfile dflags

compiler/GHC/Driver/Flags.hs

@@ -379,6 +379,7 @@ impliedGFlags = [(Opt_DeferTypeErrors, turnOn, Opt_DeferTypedHoles)
                  ,(Opt_ByteCodeAndObjectCode, turnOn, Opt_WriteByteCode)
                  ,(Opt_InfoTableMap, turnOn, Opt_InfoTableMapWithStack)
                  ,(Opt_InfoTableMap, turnOn, Opt_InfoTableMapWithFallback)
 +                ,(Opt_InfoTableMap, turnOn, Opt_Ticky_AP)
                  ] ++ validHoleFitsImpliedGFlags
  -- | General flags that are switched on/off when other general flags are switched

compiler/GHC/StgToCmm/Bind.hs

@@ -280,7 +280,7 @@ cgRhs id (StgRhsClosure fvs cc upd_flag args body _typ)
    = do
      profile <- getProfile
      check_tags <- stgToCmmDoTagCheck <$> getStgToCmmConfig
 -    use_std_ap_thunk <- stgToCmmTickyAP <$> getStgToCmmConfig
 +    use_std_ap_thunk <- stgToCmmUseStdApThunk <$> getStgToCmmConfig
      mkRhsClosure profile use_std_ap_thunk check_tags id cc (nonVoidIds (dVarSetElems fvs)) upd_flag args body
  ------------------------------------------------------------------------

compiler/GHC/StgToCmm/Config.hs

@@ -73,7 +73,7 @@ data StgToCmmConfig = StgToCmmConfig
    , stgToCmmAllowWordMul2Instr        :: !Bool   -- ^ Allowed to generate WordMul2 instruction
    , stgToCmmAllowFMAInstr             :: FMASign -> Bool -- ^ Allowed to generate FMA instruction
    , stgToCmmAllowIntWord64X2MinMax    :: !Bool   -- ^ Allowed to generate min/max instructions for Int64X2/Word64X2
 -  , stgToCmmTickyAP                   :: !Bool   -- ^ Disable use of precomputed standard thunks.
 +  , stgToCmmUseStdApThunk             :: !Bool   -- ^ Use precomputed standard AP thunks in the RTS.
    , stgToCmmSaveFCallTargetToLocal    :: !Bool   -- ^ Save a foreign call target to a Cmm local, see
                                                   -- Note [Saving foreign call target to local] for details
    ------------------------------ SIMD flags ------------------------------------