[commit: ghc] master: Properly tag fun field of PAPs generated by ap_0_fast (2693eb1)

[git at git.haskell.org]

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

On branch  : master
Link       : http://ghc.haskell.org/trac/ghc/changeset/2693eb11f55f2001701c90c24183e21c794a8be1/ghc

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

commit 2693eb11f55f2001701c90c24183e21c794a8be1
Author: Ömer Sinan Ağacan <omeragacan at gmail.com>
Date:   Tue Aug 21 16:06:29 2018 -0400

    Properly tag fun field of PAPs generated by ap_0_fast
    
    Currently ap_0_fast doesn't maintain the invariant for PAP fun fields
    which says if the closure can be tagged, it should be. This is checked
    by `Sanity.c:checkPAP` and correctly implemented by `genautoapply`.
    
    This causes sanity check failures when we have a profiling code like
    
        f = {-# SCC scc #-} g
    
    where g is a PAP or a FUN, and `scc` is different than the current cost
    centre.
    
    Test Plan: Slow validate (not done yet)
    
    Reviewers: simonmar, bgamari, erikd
    
    Reviewed By: simonmar
    
    Subscribers: rwbarton, carter
    
    GHC Trac Issues: #15508
    
    Differential Revision: https://phabricator.haskell.org/D5051


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

2693eb11f55f2001701c90c24183e21c794a8be1
 rts/Apply.cmm | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/rts/Apply.cmm b/rts/Apply.cmm
index 15d8250..7e23609 100644
--- a/rts/Apply.cmm
+++ b/rts/Apply.cmm
@@ -106,6 +106,9 @@ again:
                 pap = Hp - SIZEOF_StgPAP + WDS(1);
                 SET_HDR(pap, stg_PAP_info, CCCS);
                 StgPAP_arity(pap) = arity;
+                if (arity <= TAG_MASK) {
+                  fun = untaggedfun + arity;
+                }
                 StgPAP_fun(pap)   = fun;
                 StgPAP_n_args(pap) = 0;
                 return (pap);
@@ -117,9 +120,8 @@ again:
                 return (fun);
             } else {
                 // We're going to copy this PAP, and put the new CCS in it
-                fun = untaggedfun;
                 W_ size;
-                size = SIZEOF_StgPAP + WDS(TO_W_(StgPAP_n_args(fun)));
+                size = SIZEOF_StgPAP + WDS(TO_W_(StgPAP_n_args(untaggedfun)));
                 HP_CHK_GEN(size);
                 TICK_ALLOC_PAP(size, 0);
                 // attribute this allocation to the "overhead of profiling"
@@ -127,13 +129,13 @@ again:
                 P_ pap;
                 pap = Hp - size + WDS(1);
                 // We'll lose the original PAP, so we should enter its CCS
-                ccall enterFunCCS(BaseReg "ptr", StgHeader_ccs(fun) "ptr");
+                ccall enterFunCCS(BaseReg "ptr", StgHeader_ccs(untaggedfun) "ptr");
                 SET_HDR(pap, stg_PAP_info, CCCS);
-                StgPAP_arity(pap) = StgPAP_arity(fun);
-                StgPAP_n_args(pap) = StgPAP_n_args(fun);
+                StgPAP_arity(pap) = StgPAP_arity(untaggedfun);
+                StgPAP_n_args(pap) = StgPAP_n_args(untaggedfun);
                 StgPAP_fun(pap)   = StgPAP_fun(fun);
                 W_ i;
-                i = TO_W_(StgPAP_n_args(fun));
+                i = TO_W_(StgPAP_n_args(untaggedfun));
             loop:
                 if (i == 0) {
                     return (pap);