Marge Bot pushed to branch master at Glasgow Haskell Compiler / GHC
Commits:
3981db0c by Sylvain Henry at 2026-04-03T20:00:33-04:00
Add more canned GC functions for common register patterns (#27142)
Based on analysis of heap-check sites across the GHC compiler and Cabal,
the following patterns were not covered by existing canned GC functions
but occurred frequently enough to warrant specialisation:
stg_gc_ppppp -- 5 GC pointers
stg_gc_ip -- unboxed word + GC pointer
stg_gc_pi -- GC pointer + unboxed word
stg_gc_ii -- two unboxed words
stg_gc_bpp -- byte (I8) + two GC pointers
Adding these reduces the fraction of heap-check sites falling back to
the generic GC path from ~1.4% to ~0.4% when compiling GHC itself.
Co-Authored-By: Claude Sonnet 4.6
- - - - -
4 changed files:
- compiler/GHC/StgToCmm/Heap.hs
- rts/HeapStackCheck.cmm
- rts/RtsSymbols.c
- rts/include/stg/MiscClosures.h
Changes:
=====================================
compiler/GHC/StgToCmm/Heap.hs
=====================================
@@ -1,3 +1,4 @@
+{-# LANGUAGE OverloadedStrings #-}
-----------------------------------------------------------------------------
--
-- Stg to C--: heap management functions
@@ -44,7 +45,7 @@ import GHC.Types.Id ( Id )
import GHC.Unit
import GHC.Platform
import GHC.Platform.Profile
-import GHC.Data.FastString( mkFastString, fsLit )
+import GHC.Data.FastString( FastString )
import GHC.Utils.Panic( sorry )
import Control.Monad (when)
@@ -125,7 +126,7 @@ allocHeapClosure rep info_ptr use_cc payload = do
-- ie 1 *before* the info-ptr word of new object.
base <- getHpRelOffset info_offset
- emitComment $ mkFastString "allocHeapClosure"
+ emitComment "allocHeapClosure"
emitSetDynHdr base info_ptr use_cc
-- Fill in the fields
@@ -460,35 +461,41 @@ genericGC checkYield code
call <- mkCall generic_gc (GC, GC) [] [] updfr_sz []
heapCheck False checkYield (call <*> mkBranch lretry) code
+-- | Predefined ("canned") GC functions
+--
+-- Functions have been added to cover 99% of the GC calls made in GHC and Cabal.
+-- See #27142.
cannedGCEntryPoint :: Platform -> [LocalReg] -> Maybe CmmExpr
-cannedGCEntryPoint platform regs
- = case map localRegType regs of
- [] -> Just (mkGcLabel "stg_gc_noregs")
- [ty]
- | isGcPtrType ty -> Just (mkGcLabel "stg_gc_unpt_r1")
- | isFloatType ty -> case width of
- W32 -> Just (mkGcLabel "stg_gc_f1")
- W64 -> Just (mkGcLabel "stg_gc_d1")
- _ -> Nothing
-
- | width == wordWidth platform -> Just (mkGcLabel "stg_gc_unbx_r1")
- | width == W64 -> Just (mkGcLabel "stg_gc_l1")
- | otherwise -> Nothing
- where
- width = typeWidth ty
- [ty1,ty2]
- | isGcPtrType ty1
- && isGcPtrType ty2 -> Just (mkGcLabel "stg_gc_pp")
- [ty1,ty2,ty3]
- | isGcPtrType ty1
- && isGcPtrType ty2
- && isGcPtrType ty3 -> Just (mkGcLabel "stg_gc_ppp")
- [ty1,ty2,ty3,ty4]
- | isGcPtrType ty1
- && isGcPtrType ty2
- && isGcPtrType ty3
- && isGcPtrType ty4 -> Just (mkGcLabel "stg_gc_pppp")
- _otherwise -> Nothing
+cannedGCEntryPoint platform regs =
+ case map localRegType regs of
+ [] -> ret "stg_gc_noregs"
+ [ty]
+ | is_gc ty -> ret "stg_gc_unpt_r1"
+ | is_f32 ty -> ret "stg_gc_f1"
+ | is_f64 ty -> ret "stg_gc_d1"
+ | is_wn ty -> ret "stg_gc_unbx_r1"
+ | is_w64 ty -> ret "stg_gc_l1"
+ [ty1,ty2]
+ | is_gc ty1 && is_gc ty2 -> ret "stg_gc_pp"
+ | is_gc ty1 && is_wn ty2 -> ret "stg_gc_pi"
+ | is_wn ty1 && is_gc ty2 -> ret "stg_gc_ip"
+ | is_wn ty1 && is_wn ty2 -> ret "stg_gc_ii"
+ [ty1,ty2,ty3]
+ | is_gc ty1 && is_gc ty2 && is_gc ty3 -> ret "stg_gc_ppp"
+ | is_w8 ty1 && is_gc ty2 && is_gc ty3 -> ret "stg_gc_bpp"
+ [ty1,ty2,ty3,ty4]
+ | is_gc ty1 && is_gc ty2 && is_gc ty3 && is_gc ty4 -> ret "stg_gc_pppp"
+ [ty1,ty2,ty3,ty4,ty5]
+ | is_gc ty1 && is_gc ty2 && is_gc ty3 && is_gc ty4 && is_gc ty5 -> ret "stg_gc_ppppp"
+ _ -> Nothing
+ where
+ ret fs = Just (mkGcLabel fs)
+ is_gc ty = isGcPtrType ty
+ is_wn ty = isBitsType ty && typeWidth ty == wordWidth platform
+ is_w8 ty = isBitsType ty && typeWidth ty == W8
+ is_w64 ty = isBitsType ty && typeWidth ty == W64
+ is_f32 ty = isFloatType ty && typeWidth ty == W32
+ is_f64 ty = isFloatType ty && typeWidth ty == W64
-- Note [stg_gc arguments]
-- ~~~~~~~~~~~~~~~~~~~~~~~
@@ -514,8 +521,8 @@ generic_gc :: CmmExpr
generic_gc = mkGcLabel "stg_gc_noregs"
-- | Create a CLabel for calling a garbage collector entry point
-mkGcLabel :: String -> CmmExpr
-mkGcLabel s = CmmLit (CmmLabel (mkCmmCodeLabel rtsUnitId (fsLit s)))
+mkGcLabel :: FastString -> CmmExpr
+mkGcLabel s = CmmLit (CmmLabel (mkCmmCodeLabel rtsUnitId s))
-------------------------------
heapCheck :: Bool -> Bool -> CmmAGraph -> FCode a -> FCode a
=====================================
rts/HeapStackCheck.cmm
=====================================
@@ -373,8 +373,6 @@ stg_gc_l1 return (L_ l)
jump stg_gc_noregs (stg_ret_l_info, l) ();
}
-/*-- Unboxed tuples with multiple pointers -------------------------------- */
-
stg_gc_pp return (P_ arg1, P_ arg2)
{
call stg_gc_noregs();
@@ -393,6 +391,36 @@ stg_gc_pppp return (P_ arg1, P_ arg2, P_ arg3, P_ arg4)
return (arg1,arg2,arg3,arg4);
}
+stg_gc_ppppp return (P_ arg1, P_ arg2, P_ arg3, P_ arg4, P_ arg5)
+{
+ call stg_gc_noregs();
+ return (arg1,arg2,arg3,arg4,arg5);
+}
+
+stg_gc_ip return (W_ arg1, P_ arg2)
+{
+ call stg_gc_noregs();
+ return (arg1,arg2);
+}
+
+stg_gc_pi return (P_ arg1, W_ arg2)
+{
+ call stg_gc_noregs();
+ return (arg1,arg2);
+}
+
+stg_gc_ii return (W_ arg1, W_ arg2)
+{
+ call stg_gc_noregs();
+ return (arg1,arg2);
+}
+
+stg_gc_bpp return (I8 arg1, P_ arg2, P_ arg3)
+{
+ call stg_gc_noregs();
+ return (arg1,arg2,arg3);
+}
+
/* -----------------------------------------------------------------------------
Generic function entry heap check code.
=====================================
rts/RtsSymbols.c
=====================================
@@ -499,6 +499,11 @@ extern char **environ;
SymI_HasDataProto(stg_gc_pp) \
SymI_HasDataProto(stg_gc_ppp) \
SymI_HasDataProto(stg_gc_pppp) \
+ SymI_HasDataProto(stg_gc_ppppp) \
+ SymI_HasDataProto(stg_gc_ip) \
+ SymI_HasDataProto(stg_gc_pi) \
+ SymI_HasDataProto(stg_gc_ii) \
+ SymI_HasDataProto(stg_gc_bpp) \
SymI_HasDataProto(__stg_gc_fun) \
SymI_HasDataProto(stg_gc_fun_info) \
SymI_HasDataProto(stg_yield_noregs) \
=====================================
rts/include/stg/MiscClosures.h
=====================================
@@ -361,6 +361,11 @@ RTS_FUN_DECL(stg_gc_l1);
RTS_FUN_DECL(stg_gc_pp);
RTS_FUN_DECL(stg_gc_ppp);
RTS_FUN_DECL(stg_gc_pppp);
+RTS_FUN_DECL(stg_gc_ppppp);
+RTS_FUN_DECL(stg_gc_ip);
+RTS_FUN_DECL(stg_gc_pi);
+RTS_FUN_DECL(stg_gc_ii);
+RTS_FUN_DECL(stg_gc_bpp);
RTS_RET(stg_gc_fun);
RTS_FUN_DECL(__stg_gc_fun);
View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/3981db0ccf87e2f59b63545f250c517d...
--
View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/3981db0ccf87e2f59b63545f250c517d...
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