File aarch64_inter_far.patch of Package ghc
From 8fe9b012907fb5d84eefaa60980f7024b3951fcd Mon Sep 17 00:00:00 2001
From: Andreas Klebinger <klebinger.andreas@gmx.at>
Date: Thu, 18 Apr 2024 13:25:18 +0200
Subject: [PATCH] NCG: AArch64 - Add -finter-module-far-jumps.
When enabled the arm backend will assume jumps to targets outside of the
current module are further than 128MB away.
This will allow for code to work if:
* The current module results in less than 128MB of code.
* The whole program is loaded within a 4GB memory region.
We have seen a few reports of broken linkers (#24648) where this flag might allow
a program to compile/run successfully at a very small performance cost.
-------------------------
Metric Increase:
T783
-------------------------
(cherry picked from commit f32d6c2b468c67fed619f2fa1fb97eb012afbb6e)
---
compiler/GHC/CmmToAsm/AArch64/CodeGen.hs | 17 ++++++++++++++---
compiler/GHC/CmmToAsm/Config.hs | 1 +
compiler/GHC/Driver/Config/CmmToAsm.hs | 1 +
compiler/GHC/Driver/DynFlags.hs | 1 -
compiler/GHC/Driver/Flags.hs | 2 ++
compiler/GHC/Driver/Session.hs | 1 +
docs/users_guide/using-optimisation.rst | 17 +++++++++++++++++
7 files changed, 36 insertions(+), 4 deletions(-)
diff --git a/compiler/GHC/CmmToAsm/AArch64/CodeGen.hs b/compiler/GHC/CmmToAsm/AArch64/CodeGen.hs
index f58e507f110f..4ed3c90c7644 100644
--- a/compiler/GHC/CmmToAsm/AArch64/CodeGen.hs
+++ b/compiler/GHC/CmmToAsm/AArch64/CodeGen.hs
@@ -23,7 +23,7 @@ import GHC.Cmm.DebugBlock
import GHC.CmmToAsm.Monad
( NatM, getNewRegNat
, getPicBaseMaybeNat, getPlatform, getConfig
- , getDebugBlock, getFileId
+ , getDebugBlock, getFileId, getThisModuleNat
)
-- import GHC.CmmToAsm.Instr
import GHC.CmmToAsm.PIC
@@ -1471,8 +1471,19 @@ assignReg_FltCode = assignReg_IntCode
-- Jumps
genJump :: CmmExpr{-the branch target-} -> NatM InstrBlock
-genJump expr@(CmmLit (CmmLabel lbl))
- = return $ unitOL (annExpr expr (J (TLabel lbl)))
+genJump expr@(CmmLit (CmmLabel lbl)) = do
+ cur_mod <- getThisModuleNat
+ !useFarJumps <- ncgEnableInterModuleFarJumps <$> getConfig
+ let is_local = isLocalCLabel cur_mod lbl
+
+ -- We prefer to generate a near jump using a simble `B` instruction
+ -- with a range (+/-128MB). But if the target is outside the current module
+ -- we might have to account for large code offsets. (#24648)
+ if not useFarJumps || is_local
+ then return $ unitOL (annExpr expr (J (TLabel lbl)))
+ else do
+ (target, _format, code) <- getSomeReg expr
+ return (code `appOL` unitOL (annExpr expr (J (TReg target))))
genJump expr = do
(target, _format, code) <- getSomeReg expr
diff --git a/compiler/GHC/CmmToAsm/Config.hs b/compiler/GHC/CmmToAsm/Config.hs
index f4c39ac83c6a..422efa36ab74 100644
--- a/compiler/GHC/CmmToAsm/Config.hs
+++ b/compiler/GHC/CmmToAsm/Config.hs
@@ -47,6 +47,7 @@ data NCGConfig = NCGConfig
, ncgDwarfSourceNotes :: !Bool -- ^ Enable GHC-specific source note DIEs
, ncgCmmStaticPred :: !Bool -- ^ Enable static control-flow prediction
, ncgEnableShortcutting :: !Bool -- ^ Enable shortcutting (don't jump to blocks only containing a jump)
+ , ncgEnableInterModuleFarJumps:: !Bool -- ^ Use far-jumps for cross-module jumps.
, ncgComputeUnwinding :: !Bool -- ^ Compute block unwinding tables
, ncgEnableDeadCodeElimination :: !Bool -- ^ Whether to enable the dead-code elimination
}
diff --git a/compiler/GHC/Driver/Config/CmmToAsm.hs b/compiler/GHC/Driver/Config/CmmToAsm.hs
index 762108b8b23e..1475c40b8219 100644
--- a/compiler/GHC/Driver/Config/CmmToAsm.hs
+++ b/compiler/GHC/Driver/Config/CmmToAsm.hs
@@ -70,6 +70,7 @@ initNCGConfig dflags this_mod = NCGConfig
, ncgExposeInternalSymbols = gopt Opt_ExposeInternalSymbols dflags
, ncgCmmStaticPred = gopt Opt_CmmStaticPred dflags
, ncgEnableShortcutting = gopt Opt_AsmShortcutting dflags
+ , ncgEnableInterModuleFarJumps = gopt Opt_InterModuleFarJumps dflags
, ncgComputeUnwinding = debugLevel dflags > 0
, ncgEnableDeadCodeElimination = not (gopt Opt_InfoTableMap dflags)
-- Disable when -finfo-table-map is on (#20428)
diff --git a/compiler/GHC/Driver/DynFlags.hs b/compiler/GHC/Driver/DynFlags.hs
index a24ea13e5caa..469537b7caa2 100644
--- a/compiler/GHC/Driver/DynFlags.hs
+++ b/compiler/GHC/Driver/DynFlags.hs
@@ -1194,7 +1194,6 @@ defaultFlags settings
++ validHoleFitDefaults
-
where platform = sTargetPlatform settings
-- | These are the default settings for the display and sorting of valid hole
diff --git a/compiler/GHC/Driver/Flags.hs b/compiler/GHC/Driver/Flags.hs
index 583a8530eca7..fc8d75ed13fe 100644
--- a/compiler/GHC/Driver/Flags.hs
+++ b/compiler/GHC/Driver/Flags.hs
@@ -647,6 +647,7 @@ data GeneralFlag
| Opt_CmmElimCommonBlocks
| Opt_CmmControlFlow
| Opt_AsmShortcutting
+ | Opt_InterModuleFarJumps
| Opt_OmitYields
| Opt_FunToThunk -- deprecated
| Opt_DictsStrict -- be strict in argument dictionaries
@@ -896,6 +897,7 @@ optimisationFlags = EnumSet.fromList
, Opt_CmmSink
, Opt_CmmElimCommonBlocks
, Opt_AsmShortcutting
+ , Opt_InterModuleFarJumps
, Opt_FunToThunk
, Opt_DmdTxDictSel
, Opt_Loopification
diff --git a/compiler/GHC/Driver/Session.hs b/compiler/GHC/Driver/Session.hs
index 74490ba91f9b..804e11b28d90 100644
--- a/compiler/GHC/Driver/Session.hs
+++ b/compiler/GHC/Driver/Session.hs
@@ -2453,6 +2453,7 @@ fFlagsDeps = [
flagSpec "gen-manifest" Opt_GenManifest,
flagSpec "ghci-history" Opt_GhciHistory,
flagSpec "ghci-leak-check" Opt_GhciLeakCheck,
+ flagSpec "inter-module-far-jumps" Opt_InterModuleFarJumps,
flagSpec "validate-ide-info" Opt_ValidateHie,
flagGhciSpec "local-ghci-history" Opt_LocalGhciHistory,
flagGhciSpec "no-it" Opt_NoIt,
diff --git a/docs/users_guide/using-optimisation.rst b/docs/users_guide/using-optimisation.rst
index f57a1ba32278..ffb371150edd 100644
--- a/docs/users_guide/using-optimisation.rst
+++ b/docs/users_guide/using-optimisation.rst
@@ -681,6 +681,23 @@ as such you shouldn't need to set any of them explicitly. A flag
``-fno-full-laziness``. If that is inconvenient for you, please leave a
comment `on the issue tracker (#21204) <https://gitlab.haskell.org/ghc/ghc/-/issues/21204>`__.
+.. ghc-flag:: -finter-module-far-jumps
+ :shortdesc: Assume code sections can be very large.
+ :type: dynamic
+ :reverse: -fno-inter-module-far-jumps
+ :category:
+
+ :default: Off
+
+ This flag forces GHC to use far jumps instead of near jumps for all jumps
+ which cross module boundries. This removes the need for jump islands/linker
+ jump fixups which some linkers struggle to deal with. (:ghc-ticket:`24648`)
+
+ This comes at a very modest code size (~2%) and runtime (~0.6%) overhead.
+
+ Note that this flag currently only affects the NCG AArch64 backend.
+
+
.. ghc-flag:: -fignore-asserts
:shortdesc: Ignore assertions in the source. Implied by :ghc-flag:`-O`.
:type: dynamic
--
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