[Git][ghc/ghc][wip/memory-barriers] Drop unnecessary (and seemingly incorrect) changes in Compact.cmm

[Ben Gamari]

Ben Gamari pushed to branch wip/memory-barriers at Glasgow Haskell Compiler / GHC


Commits:
ee6ba25b by Ben Gamari at 2019-06-11T18:04:51Z
Drop unnecessary (and seemingly incorrect) changes in Compact.cmm

- - - - -


1 changed file:

- rts/Compact.cmm


Changes:

=====================================
rts/Compact.cmm
=====================================
@@ -53,6 +53,9 @@ import CLOSURE base_GHCziIOziException_cannotCompactPinned_closure;
 // data structure.  It takes the location to store the address of the
 // compacted object as an argument, so that it can be tail-recursive.
 //
+// N.B. No memory barrier (see Note [Heap memory barriers] in SMP.h) is needed
+// here since this is essentially an allocation of a new object which won't
+// be visible to other cores until after we return.
 stg_compactAddWorkerzh (
     P_ compact,  // The Compact# object
     P_ p,        // The object to compact
@@ -169,6 +172,7 @@ eval:
         cards = SIZEOF_StgMutArrPtrs + WDS(ptrs);
         ALLOCATE(compact, BYTES_TO_WDS(size), p, to, tag);
         P_[pp] = tag | to;
+        SET_HDR(to, StgHeader_info(p), StgHeader_ccs(p));
         StgMutArrPtrs_ptrs(to) = ptrs;
         StgMutArrPtrs_size(to) = StgMutArrPtrs_size(p);
         prim %memcpy(to + cards, p + cards , size - cards, 1);
@@ -182,7 +186,6 @@ eval:
             i = i + 1;
             goto loop0;
         }
-        SET_HDR(to, StgHeader_info(p), StgHeader_ccs(p));
         return();
     }
 
@@ -199,6 +202,7 @@ eval:
         ptrs = StgSmallMutArrPtrs_ptrs(p);
         ALLOCATE(compact, BYTES_TO_WDS(SIZEOF_StgSmallMutArrPtrs) + ptrs, p, to, tag);
         P_[pp] = tag | to;
+        SET_HDR(to, StgHeader_info(p), StgHeader_ccs(p));
         StgSmallMutArrPtrs_ptrs(to) = ptrs;
         i = 0;
       loop1:
@@ -210,7 +214,6 @@ eval:
             i = i + 1;
             goto loop1;
         }
-        SET_HDR(to, StgHeader_info(p), StgHeader_ccs(p));
         return();
     }
 
@@ -236,6 +239,7 @@ eval:
 
         ALLOCATE(compact, size, p, to, tag);
         P_[pp] = tag | to;
+        SET_HDR(to, StgHeader_info(p), StgHeader_ccs(p));
 
         // First, copy the non-pointers
         if (nptrs > 0) {
@@ -245,7 +249,6 @@ eval:
             i = i + 1;
             if (i < ptrs + nptrs) ( likely: True ) goto loop2;
         }
-        SET_HDR(to, StgHeader_info(p), StgHeader_ccs(p));
 
         // Next, recursively compact and copy the pointers
         if (ptrs == 0) { return(); }



View it on GitLab: https://gitlab.haskell.org/ghc/ghc/commit/ee6ba25b1b407a9516b55b94ea90dad176eb49ca

-- 
View it on GitLab: https://gitlab.haskell.org/ghc/ghc/commit/ee6ba25b1b407a9516b55b94ea90dad176eb49ca
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