[commit: ghc] master: Remove unnecessary check in simplCast (2a5bdd9)

[git at git.haskell.org]

Repository : ssh://git@git.haskell.org/ghc

On branch  : master
Link       : http://ghc.haskell.org/trac/ghc/changeset/2a5bdd9adb1cb4afecd3303f0cfcc224be5ce745/ghc

>---------------------------------------------------------------

commit 2a5bdd9adb1cb4afecd3303f0cfcc224be5ce745
Author: Tobias Dammers <tdammers at gmail.com>
Date:   Fri Apr 20 16:38:34 2018 -0400

    Remove unnecessary check in simplCast
    
    The coercion optimizer will take care of it anyway, and the check is
    prohibitively expensive.
    
    See Trac #14737.
    
    Reviewers: bgamari
    
    Subscribers: simonpj, thomie, carter
    
    Differential Revision: https://phabricator.haskell.org/D4568


>---------------------------------------------------------------

2a5bdd9adb1cb4afecd3303f0cfcc224be5ce745
 compiler/coreSyn/CoreOpt.hs         | 12 ++++++++----
 testsuite/tests/perf/compiler/all.T | 12 ++++++++----
 2 files changed, 16 insertions(+), 8 deletions(-)

diff --git a/compiler/coreSyn/CoreOpt.hs b/compiler/coreSyn/CoreOpt.hs
index 372c2ea..f1ff68d 100644
--- a/compiler/coreSyn/CoreOpt.hs
+++ b/compiler/coreSyn/CoreOpt.hs
@@ -958,8 +958,10 @@ pushCoTyArg :: CoercionR -> Type -> Maybe (Type, Maybe CoercionR)
 -- If the returned coercion is Nothing, then it would have been reflexive;
 -- it's faster not to compute it, though.
 pushCoTyArg co ty
-  | tyL `eqType` tyR
-  = Just (ty, Nothing)
+  -- The following is inefficient - don't do `eqType` here, the coercion
+  -- optimizer will take care of it. See Trac #14737.
+  -- -- | tyL `eqType` tyR
+  -- -- = Just (ty, Nothing)
 
   | isForAllTy tyL
   = ASSERT2( isForAllTy tyR, ppr co $$ ppr ty )
@@ -991,8 +993,10 @@ pushCoValArg :: CoercionR -> Maybe (Coercion, Maybe Coercion)
 -- If the second returned Coercion is actually Nothing, then no cast is necessary;
 -- the returned coercion would have been reflexive.
 pushCoValArg co
-  | tyL `eqType` tyR
-  = Just (mkRepReflCo arg, Nothing)
+  -- The following is inefficient - don't do `eqType` here, the coercion
+  -- optimizer will take care of it. See Trac #14737.
+  -- -- | tyL `eqType` tyR
+  -- -- = Just (mkRepReflCo arg, Nothing)
 
   | isFunTy tyL
   , (co1, co2) <- decomposeFunCo Representational co
diff --git a/testsuite/tests/perf/compiler/all.T b/testsuite/tests/perf/compiler/all.T
index ba36b41..2001cda 100644
--- a/testsuite/tests/perf/compiler/all.T
+++ b/testsuite/tests/perf/compiler/all.T
@@ -747,7 +747,7 @@ test('T9020',
            # 2014-07-31:  343005716 (Windows) (general round of updates)
            # 2017-03-24:  249904136 (x86/Linux, 64-bit machine)
 
-           (wordsize(64), 423163832, 10)])
+           (wordsize(64), 562206104, 10)])
            # prev:        795469104
            # 2014-07-17:  728263536 (general round of updates)
            # 2014-09-10:  785871680 post-AMP-cleanup
@@ -761,6 +761,7 @@ test('T9020',
            #                        Program size collapses in first simplification
            # 2017-03-31:  493596312 Fix memory leak in simplifier
            # 2017-04-28:  423163832  Remove exponential behaviour in simplifier
+           # 2018-04-09:  562206104 Inexplicable, collateral of #14737
       ],
       compile,[''])
 
@@ -1039,7 +1040,7 @@ test('T12227',
 test('T12425',
      [ only_ways(['optasm']),
        compiler_stats_num_field('bytes allocated',
-          [(wordsize(64), 134780272, 5),
+          [(wordsize(64), 141952368, 5),
           # initial:      125831400
           # 2017-01-18:   133380960  Allow top-level string literals in Core
           # 2017-02-17:   153611448  Type-indexed Typeable
@@ -1047,6 +1048,7 @@ test('T12425',
           # 2017-03-21:   134334800  Unclear
           # 2017-04-28:   127500136  Remove exponential behaviour in simplifier
           # 2017-05-23:   134780272  Addition of llvm-targets in dynflags (D3352)
+          # 2018-04-15:   141952368  Collateral of #14737
           ]),
      ],
      compile,
@@ -1116,7 +1118,7 @@ test('T13056',
 
 test('T12707',
      [ compiler_stats_num_field('bytes allocated',
-          [(wordsize(64), 1163821528, 5),
+          [(wordsize(64), 1237898376, 5),
           # initial:    1271577192
           # 2017-01-22: 1348865648  Allow top-level strings in Core
           # 2017-01-31: 1280336112  Join points (#12988)
@@ -1124,6 +1126,7 @@ test('T12707',
           # 2017-02-23: 1386110512  Type-indexed Typeable? (on Darwin)
           # 2017-03-02: 1231809592  Drift from recent simplifier improvements
           # 2017-05-14: 1163821528  (amd64/Linux) Two-pass CmmLayoutStack
+          # 2018-04-09: 1237898376  Inexplicable, collateral of #14737
           ]),
      ],
      compile,
@@ -1235,9 +1238,10 @@ test('T14697',
 
 test('T14683',
      [ compiler_stats_num_field('bytes allocated',
-          [(wordsize(64), 14675353056, 10),
+          [(wordsize(64), 10521594688, 10),
           # initial:      25189145632
           # 2018-04-19:   14675353056  Cache NthCo role (#14683)
+          # 2018-04-20:   10521594688  Remove unnecessary check in simplCast
           ]),
      ],
      multimod_compile,