From 6e361d895dda4600a85e01c72ff219474b5c7190 Mon Sep 17 00:00:00 2001
From: Kavon Farvardin <kavon@farvard.in>
Date: Thu, 4 Oct 2018 13:44:55 -0400
Subject: [PATCH] Multiple fixes / improvements for LLVM backend
- Fix for #13904 -- stop "trashing" callee-saved registers, since it is
not actually doing anything useful.
- Fix for #14251 -- fixes the calling convention for functions passing
raw SSE-register values by adding padding as needed to get the values
in the right registers. This problem cropped up when some args were
unused an dropped from the live list.
- Fixed a typo in 'readnone' attribute
- Added 'lower-expect' pass to level 0 LLVM optimization passes to
improve block layout in LLVM for stack checks, etc.
Test Plan: `make test WAYS=optllvm` and `make test WAYS=llvm`
Reviewers: bgamari, simonmar, angerman
Reviewed By: angerman
Subscribers: rwbarton, carter
GHC Trac Issues: #13904, #14251
Differential Revision: https://phabricator.haskell.org/D5190
(cherry picked from commit adcb5fb47c0942671d409b940d8884daa9359ca4)
---
compiler/llvmGen/Llvm/Types.hs | 2 +-
compiler/llvmGen/LlvmCodeGen/Base.hs | 62 ++++++++++++++++++++----
compiler/llvmGen/LlvmCodeGen/CodeGen.hs | 59 +++++-----------------
compiler/main/DriverPipeline.hs | 2 +-
testsuite/tests/codeGen/should_run/all.T | 4 +-
5 files changed, 67 insertions(+), 62 deletions(-)
diff --git a/compiler/llvmGen/Llvm/Types.hs b/compiler/llvmGen/Llvm/Types.hs
index 87111499fc0..c1c51afcf0f 100644
--- a/compiler/llvmGen/Llvm/Types.hs
+++ b/compiler/llvmGen/Llvm/Types.hs
@@ -560,7 +560,7 @@ instance Outputable LlvmFuncAttr where
ppr OptSize = text "optsize"
ppr NoReturn = text "noreturn"
ppr NoUnwind = text "nounwind"
- ppr ReadNone = text "readnon"
+ ppr ReadNone = text "readnone"
ppr ReadOnly = text "readonly"
ppr Ssp = text "ssp"
ppr SspReq = text "ssqreq"
diff --git a/compiler/llvmGen/LlvmCodeGen/Base.hs b/compiler/llvmGen/LlvmCodeGen/Base.hs
index 6e20da48c1b..ec91bacc4c8 100644
--- a/compiler/llvmGen/LlvmCodeGen/Base.hs
+++ b/compiler/llvmGen/LlvmCodeGen/Base.hs
@@ -26,7 +26,7 @@ module LlvmCodeGen.Base (
cmmToLlvmType, widthToLlvmFloat, widthToLlvmInt, llvmFunTy,
llvmFunSig, llvmFunArgs, llvmStdFunAttrs, llvmFunAlign, llvmInfAlign,
- llvmPtrBits, tysToParams, llvmFunSection,
+ llvmPtrBits, tysToParams, llvmFunSection, padLiveArgs, isSSE,
strCLabel_llvm, strDisplayName_llvm, strProcedureName_llvm,
getGlobalPtr, generateExternDecls,
@@ -58,6 +58,8 @@ import ErrUtils
import qualified Stream
import Control.Monad (ap)
+import Data.List (sort)
+import Data.Maybe (mapMaybe)
-- ----------------------------------------------------------------------------
-- * Some Data Types
@@ -147,16 +149,58 @@ llvmFunSection dflags lbl
-- | A Function's arguments
llvmFunArgs :: DynFlags -> LiveGlobalRegs -> [LlvmVar]
llvmFunArgs dflags live =
- map (lmGlobalRegArg dflags) (filter isPassed (activeStgRegs platform))
+ map (lmGlobalRegArg dflags) (filter isPassed allRegs)
where platform = targetPlatform dflags
- isLive r = not (isSSE r) || r `elem` alwaysLive || r `elem` live
+ allRegs = activeStgRegs platform
+ paddedLive = map (\(_,r) -> r) $ padLiveArgs live
+ isLive r = r `elem` alwaysLive || r `elem` paddedLive
isPassed r = not (isSSE r) || isLive r
- isSSE (FloatReg _) = True
- isSSE (DoubleReg _) = True
- isSSE (XmmReg _) = True
- isSSE (YmmReg _) = True
- isSSE (ZmmReg _) = True
- isSSE _ = False
+
+
+isSSE :: GlobalReg -> Bool
+isSSE (FloatReg _) = True
+isSSE (DoubleReg _) = True
+isSSE (XmmReg _) = True
+isSSE (YmmReg _) = True
+isSSE (ZmmReg _) = True
+isSSE _ = False
+
+sseRegNum :: GlobalReg -> Maybe Int
+sseRegNum (FloatReg i) = Just i
+sseRegNum (DoubleReg i) = Just i
+sseRegNum (XmmReg i) = Just i
+sseRegNum (YmmReg i) = Just i
+sseRegNum (ZmmReg i) = Just i
+sseRegNum _ = Nothing
+
+-- the bool indicates whether the global reg was added as padding.
+-- the returned list is not sorted in any particular order,
+-- but does indicate the set of live registers needed, with SSE padding.
+padLiveArgs :: LiveGlobalRegs -> [(Bool, GlobalReg)]
+padLiveArgs live = allRegs
+ where
+ sseRegNums = sort $ mapMaybe sseRegNum live
+ (_, padding) = foldl assignSlots (1, []) $ sseRegNums
+ allRegs = padding ++ map (\r -> (False, r)) live
+
+ assignSlots (i, acc) regNum
+ | i == regNum = -- don't need padding here
+ (i+1, acc)
+ | i < regNum = let -- add padding for slots i .. regNum-1
+ numNeeded = regNum-i
+ acc' = genPad i numNeeded ++ acc
+ in
+ (regNum+1, acc')
+ | otherwise = error "padLiveArgs -- i > regNum ??"
+
+ genPad start n =
+ take n $ flip map (iterate (+1) start) (\i ->
+ (True, FloatReg i))
+ -- NOTE: Picking float should be fine for the following reasons:
+ -- (1) Float aliases with all the other SSE register types on
+ -- the given platform.
+ -- (2) The argument is not live anyways.
+
-- | Llvm standard fun attributes
llvmStdFunAttrs :: [LlvmFuncAttr]
diff --git a/compiler/llvmGen/LlvmCodeGen/CodeGen.hs b/compiler/llvmGen/LlvmCodeGen/CodeGen.hs
index e812dd445f1..a7121b7909a 100644
--- a/compiler/llvmGen/LlvmCodeGen/CodeGen.hs
+++ b/compiler/llvmGen/LlvmCodeGen/CodeGen.hs
@@ -14,7 +14,7 @@ import LlvmCodeGen.Base
import LlvmCodeGen.Regs
import BlockId
-import CodeGen.Platform ( activeStgRegs, callerSaves )
+import CodeGen.Platform ( activeStgRegs )
import CLabel
import Cmm
import PprCmm
@@ -211,7 +211,6 @@ genCall t@(PrimTarget (MO_Prefetch_Data localityInt)) [] args
fptr <- liftExprData $ getFunPtr funTy t
argVars' <- castVarsW Signed $ zip argVars argTy
- doTrashStmts
let argSuffix = [mkIntLit i32 0, mkIntLit i32 localityInt, mkIntLit i32 1]
statement $ Expr $ Call StdCall fptr (argVars' ++ argSuffix) []
| otherwise = panic $ "prefetch locality level integer must be between 0 and 3, given: " ++ (show localityInt)
@@ -294,7 +293,6 @@ genCall t@(PrimTarget op) [] args
fptr <- getFunPtrW funTy t
argVars' <- castVarsW Signed $ zip argVars argTy
- doTrashStmts
let alignVal = mkIntLit i32 align
arguments = argVars' ++ (alignVal:isVolVal)
statement $ Expr $ Call StdCall fptr arguments []
@@ -446,7 +444,6 @@ genCall target res args = runStmtsDecls $ do
| never_returns = statement $ Unreachable
| otherwise = return ()
- doTrashStmts
-- make the actual call
case retTy of
@@ -1759,12 +1756,9 @@ genLit _ CmmHighStackMark
funPrologue :: LiveGlobalRegs -> [CmmBlock] -> LlvmM StmtData
funPrologue live cmmBlocks = do
- trash <- getTrashRegs
let getAssignedRegs :: CmmNode O O -> [CmmReg]
getAssignedRegs (CmmAssign reg _) = [reg]
- -- Calls will trash all registers. Unfortunately, this needs them to
- -- be stack-allocated in the first place.
- getAssignedRegs (CmmUnsafeForeignCall _ rs _) = map CmmGlobal trash ++ map CmmLocal rs
+ getAssignedRegs (CmmUnsafeForeignCall _ rs _) = map CmmLocal rs
getAssignedRegs _ = []
getRegsBlock (_, body, _) = concatMap getAssignedRegs $ blockToList body
assignedRegs = nub $ concatMap (getRegsBlock . blockSplit) cmmBlocks
@@ -1794,14 +1788,9 @@ funPrologue live cmmBlocks = do
funEpilogue :: LiveGlobalRegs -> LlvmM ([LlvmVar], LlvmStatements)
funEpilogue live = do
- -- Have information and liveness optimisation is enabled?
- let liveRegs = alwaysLive ++ live
- isSSE (FloatReg _) = True
- isSSE (DoubleReg _) = True
- isSSE (XmmReg _) = True
- isSSE (YmmReg _) = True
- isSSE (ZmmReg _) = True
- isSSE _ = False
+ -- the bool indicates whether the register is padding.
+ let alwaysNeeded = map (\r -> (False, r)) alwaysLive
+ livePadded = alwaysNeeded ++ padLiveArgs live
-- Set to value or "undef" depending on whether the register is
-- actually live
@@ -1813,39 +1802,17 @@ funEpilogue live = do
let ty = (pLower . getVarType $ lmGlobalRegVar dflags r)
return (Just $ LMLitVar $ LMUndefLit ty, nilOL)
platform <- getDynFlag targetPlatform
- loads <- flip mapM (activeStgRegs platform) $ \r -> case () of
- _ | r `elem` liveRegs -> loadExpr r
- | not (isSSE r) -> loadUndef r
+ let allRegs = activeStgRegs platform
+ loads <- flip mapM allRegs $ \r -> case () of
+ _ | (False, r) `elem` livePadded
+ -> loadExpr r -- if r is not padding, load it
+ | not (isSSE r) || (True, r) `elem` livePadded
+ -> loadUndef r
| otherwise -> return (Nothing, nilOL)
let (vars, stmts) = unzip loads
return (catMaybes vars, concatOL stmts)
-
--- | A series of statements to trash all the STG registers.
---
--- In LLVM we pass the STG registers around everywhere in function calls.
--- So this means LLVM considers them live across the entire function, when
--- in reality they usually aren't. For Caller save registers across C calls
--- the saving and restoring of them is done by the Cmm code generator,
--- using Cmm local vars. So to stop LLVM saving them as well (and saving
--- all of them since it thinks they're always live, we trash them just
--- before the call by assigning the 'undef' value to them. The ones we
--- need are restored from the Cmm local var and the ones we don't need
--- are fine to be trashed.
-getTrashStmts :: LlvmM LlvmStatements
-getTrashStmts = do
- regs <- getTrashRegs
- stmts <- flip mapM regs $ \ r -> do
- reg <- getCmmReg (CmmGlobal r)
- let ty = (pLower . getVarType) reg
- return $ Store (LMLitVar $ LMUndefLit ty) reg
- return $ toOL stmts
-
-getTrashRegs :: LlvmM [GlobalReg]
-getTrashRegs = do plat <- getLlvmPlatform
- return $ filter (callerSaves plat) (activeStgRegs plat)
-
-- | Get a function pointer to the CLabel specified.
--
-- This is for Haskell functions, function type is assumed, so doesn't work
@@ -1967,7 +1934,3 @@ getCmmRegW = lift . getCmmReg
genLoadW :: Atomic -> CmmExpr -> CmmType -> WriterT LlvmAccum LlvmM LlvmVar
genLoadW atomic e ty = liftExprData $ genLoad atomic e ty
-doTrashStmts :: WriterT LlvmAccum LlvmM ()
-doTrashStmts = do
- stmts <- lift getTrashStmts
- tell $ LlvmAccum stmts mempty
diff --git a/compiler/main/DriverPipeline.hs b/compiler/main/DriverPipeline.hs
index 86dd913461c..f4d5e7f553c 100644
--- a/compiler/main/DriverPipeline.hs
+++ b/compiler/main/DriverPipeline.hs
@@ -1465,7 +1465,7 @@ runPhase (RealPhase LlvmOpt) input_fn dflags
-- we always (unless -optlo specified) run Opt since we rely on it to
-- fix up some pretty big deficiencies in the code we generate
llvmOpts = case optLevel dflags of
- 0 -> "-mem2reg -globalopt"
+ 0 -> "-mem2reg -globalopt -lower-expect"
1 -> "-O1 -globalopt"
_ -> "-O2"