[commit: ghc] ghc-8.6: Run StgCse after unarise, fixes #15300 (72dc798)
git at git.haskell.org
git at git.haskell.org
Mon Jul 30 22:26:45 UTC 2018
Repository : ssh://git@git.haskell.org/ghc
On branch : ghc-8.6
Link : http://ghc.haskell.org/trac/ghc/changeset/72dc7989a25ed6ec4ab9d3adfeefc15425acbf57/ghc
>---------------------------------------------------------------
commit 72dc7989a25ed6ec4ab9d3adfeefc15425acbf57
Author: Ömer Sinan Ağacan <omeragacan at gmail.com>
Date: Thu Jul 26 17:19:35 2018 -0400
Run StgCse after unarise, fixes #15300
Given two unboxed sum terms:
(# 1 | #) :: (# Int | Int# #)
(# 1 | #) :: (# Int | Int #)
These two terms are not equal as they unarise to different unboxed
tuples. However StgCse was thinking that these are equal, and replacing
one of these with a binder to the other.
To not deal with unboxed sums in StgCse we now do it after unarise. For
StgCse to maintain post-unarise invariants we factor-out case binder
in-scopeness check to `stgCaseBndrInScope` and use it in StgCse.
Also did some refactoring in SimplStg.
Another way to fix this would be adding a special case in StgCse to not
bring unboxed sum binders in scope:
diff --git a/compiler/simplStg/StgCse.hs
b/compiler/simplStg/StgCse.hs
index 6c740ca4cb..93a0f8f6ad 100644
--- a/compiler/simplStg/StgCse.hs
+++ b/compiler/simplStg/StgCse.hs
@@ -332,7 +332,11 @@ stgCseExpr env (StgLetNoEscape binds body)
stgCseAlt :: CseEnv -> OutId -> InStgAlt -> OutStgAlt
stgCseAlt env case_bndr (DataAlt dataCon, args, rhs)
= let (env1, args') = substBndrs env args
- env2 = addDataCon case_bndr dataCon (map StgVarArg
args') env1
+ env2
+ | isUnboxedSumCon dataCon
+ = env1
+ | otherwise
+ = addDataCon case_bndr dataCon (map StgVarArg args')
env1
-- see note [Case 2: CSEing case binders]
rhs' = stgCseExpr env2 rhs
in (DataAlt dataCon, args', rhs')
I think this patch seems better in that it doesn't add a special case to
StgCse.
Test Plan:
Validate.
I tried to come up with a minimal example but failed. I thought a simple
program like
data T = T (# Int | Int #) (# Int# | Int #)
case T (# 1 | #) (# 1 | #) of ...
should be enough to trigger this bug, but for some reason StgCse
doesn't do
anything on this program.
Reviewers: simonpj, bgamari
Reviewed By: simonpj
Subscribers: rwbarton, thomie, carter
GHC Trac Issues: #15300
Differential Revision: https://phabricator.haskell.org/D4962
(cherry picked from commit 3c311e50e760c3ba00dc9692ad1536c79820598d)
>---------------------------------------------------------------
72dc7989a25ed6ec4ab9d3adfeefc15425acbf57
compiler/simplStg/SimplStg.hs | 26 ++++++++------------------
compiler/simplStg/StgCse.hs | 20 +++++++++++++++-----
compiler/stgSyn/StgLint.hs | 10 +---------
compiler/stgSyn/StgSyn.hs | 13 +++++++++++++
testsuite/tests/simplStg/should_compile/all.T | 4 +---
5 files changed, 38 insertions(+), 35 deletions(-)
diff --git a/compiler/simplStg/SimplStg.hs b/compiler/simplStg/SimplStg.hs
index 854bb92..36bf510 100644
--- a/compiler/simplStg/SimplStg.hs
+++ b/compiler/simplStg/SimplStg.hs
@@ -21,7 +21,6 @@ import StgCse ( stgCse )
import DynFlags
import ErrUtils
-import SrcLoc
import UniqSupply ( mkSplitUniqSupply )
import Outputable
import Control.Monad
@@ -34,27 +33,19 @@ stg2stg dflags binds
= do { showPass dflags "Stg2Stg"
; us <- mkSplitUniqSupply 'g'
- ; when (dopt Opt_D_verbose_stg2stg dflags)
- (putLogMsg dflags NoReason SevDump noSrcSpan
- (defaultDumpStyle dflags) (text "VERBOSE STG-TO-STG:"))
-
- ; binds' <- end_pass "Stg2Stg" binds
-
-- Do the main business!
- ; processed_binds <- foldM do_stg_pass binds' (getStgToDo dflags)
-
; dumpIfSet_dyn dflags Opt_D_dump_stg "Pre unarise:"
- (pprStgTopBindings processed_binds)
-
- ; let un_binds = unarise us processed_binds
+ (pprStgTopBindings binds)
+ ; stg_linter False "Pre-unarise" binds
+ ; let un_binds = unarise us binds
; stg_linter True "Unarise" un_binds
; dumpIfSet_dyn dflags Opt_D_dump_stg "STG syntax:"
(pprStgTopBindings un_binds)
- ; return un_binds
- }
+ ; foldM do_stg_pass un_binds (getStgToDo dflags)
+ }
where
stg_linter unarised
@@ -65,8 +56,7 @@ stg2stg dflags binds
do_stg_pass binds to_do
= case to_do of
D_stg_stats ->
- trace (showStgStats binds)
- end_pass "StgStats" binds
+ trace (showStgStats binds) (return binds)
StgCSE ->
{-# SCC "StgCse" #-}
@@ -78,8 +68,8 @@ stg2stg dflags binds
end_pass what binds2
= do -- report verbosely, if required
dumpIfSet_dyn dflags Opt_D_verbose_stg2stg what
- (vcat (map ppr binds2))
- stg_linter False what binds2
+ (pprStgTopBindings binds2)
+ stg_linter True what binds2
return binds2
-- -----------------------------------------------------------------------------
diff --git a/compiler/simplStg/StgCse.hs b/compiler/simplStg/StgCse.hs
index 6c740ca..1ae1213 100644
--- a/compiler/simplStg/StgCse.hs
+++ b/compiler/simplStg/StgCse.hs
@@ -302,7 +302,7 @@ stgCseExpr env (StgCase scrut bndr ty alts)
env2 | StgApp trivial_scrut [] <- scrut' = addTrivCaseBndr bndr trivial_scrut env1
-- See Note [Trivial case scrutinee]
| otherwise = env1
- alts' = map (stgCseAlt env2 bndr') alts
+ alts' = map (stgCseAlt env2 ty bndr') alts
-- A constructor application.
@@ -329,14 +329,24 @@ stgCseExpr env (StgLetNoEscape binds body)
-- Case alternatives
-- Extend the CSE environment
-stgCseAlt :: CseEnv -> OutId -> InStgAlt -> OutStgAlt
-stgCseAlt env case_bndr (DataAlt dataCon, args, rhs)
+stgCseAlt :: CseEnv -> AltType -> OutId -> InStgAlt -> OutStgAlt
+stgCseAlt env ty case_bndr (DataAlt dataCon, args, rhs)
= let (env1, args') = substBndrs env args
- env2 = addDataCon case_bndr dataCon (map StgVarArg args') env1
+ env2
+ -- To avoid dealing with unboxed sums StgCse runs after unarise and
+ -- should maintain invariants listed in Note [Post-unarisation
+ -- invariants]. One of the invariants is that some binders are not
+ -- used (unboxed tuple case binders) which is what we check with
+ -- `stgCaseBndrInScope` here. If the case binder is not in scope we
+ -- don't add it to the CSE env. See also #15300.
+ | stgCaseBndrInScope ty True -- CSE runs after unarise
+ = addDataCon case_bndr dataCon (map StgVarArg args') env1
+ | otherwise
+ = env1
-- see note [Case 2: CSEing case binders]
rhs' = stgCseExpr env2 rhs
in (DataAlt dataCon, args', rhs')
-stgCseAlt env _ (altCon, args, rhs)
+stgCseAlt env _ _ (altCon, args, rhs)
= let (env1, args') = substBndrs env args
rhs' = stgCseExpr env1 rhs
in (altCon, args', rhs')
diff --git a/compiler/stgSyn/StgLint.hs b/compiler/stgSyn/StgLint.hs
index bb2064a..58f14a1 100644
--- a/compiler/stgSyn/StgLint.hs
+++ b/compiler/stgSyn/StgLint.hs
@@ -172,15 +172,7 @@ lintStgExpr (StgCase scrut bndr alts_type alts) = do
lintStgExpr scrut
lf <- getLintFlags
- let in_scope =
- case alts_type of
- AlgAlt _ -> True
- PrimAlt _ -> True
- -- Case binders of unboxed tuple or unboxed sum type always dead
- -- after the unariser has run.
- -- See Note [Post-unarisation invariants].
- MultiValAlt _ -> not (lf_unarised lf)
- PolyAlt -> True
+ let in_scope = stgCaseBndrInScope alts_type (lf_unarised lf)
addInScopeVars [bndr | in_scope] (mapM_ lintAlt alts)
diff --git a/compiler/stgSyn/StgSyn.hs b/compiler/stgSyn/StgSyn.hs
index 608a028..eb905f7 100644
--- a/compiler/stgSyn/StgSyn.hs
+++ b/compiler/stgSyn/StgSyn.hs
@@ -39,6 +39,7 @@ module StgSyn (
isDllConApp,
stgArgType,
stripStgTicksTop,
+ stgCaseBndrInScope,
pprStgBinding, pprStgTopBindings
) where
@@ -155,6 +156,18 @@ stripStgTicksTop p = go []
where go ts (StgTick t e) | p t = go (t:ts) e
go ts other = (reverse ts, other)
+-- | Given an alt type and whether the program is unarised, return whether the
+-- case binder is in scope.
+--
+-- Case binders of unboxed tuple or unboxed sum type always dead after the
+-- unariser has run. See Note [Post-unarisation invariants].
+stgCaseBndrInScope :: AltType -> Bool {- ^ unarised? -} -> Bool
+stgCaseBndrInScope alt_ty unarised =
+ case alt_ty of
+ AlgAlt _ -> True
+ PrimAlt _ -> True
+ MultiValAlt _ -> not unarised
+ PolyAlt -> True
{-
************************************************************************
diff --git a/testsuite/tests/simplStg/should_compile/all.T b/testsuite/tests/simplStg/should_compile/all.T
index 19fa513..2cb8974 100644
--- a/testsuite/tests/simplStg/should_compile/all.T
+++ b/testsuite/tests/simplStg/should_compile/all.T
@@ -17,6 +17,4 @@ def checkStgString(needle):
return "%s not contained in -ddump-simpl\n" % needle
return normalise_errmsg_fun(norm)
-
-
-test('T13588', [ checkStgString('case') ] , compile, ['-ddump-stg'])
+test('T13588', [ checkStgString('case') ] , compile, ['-dverbose-stg2stg'])
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