Marge Bot pushed to branch master at Glasgow Haskell Compiler / GHC Commits: cdb74049 by Cheng Shao at 2026-01-22T14:52:36-05:00 rts: avoid Cmm loop to initialize Array#/SmallArray# Previously, `newArray#`/`newSmallArray#` called an RTS C function to allocate the `Array#`/`SmallArray#`, then used a Cmm loop to initialize the elements. Cmm doesn't have native for-loop so the code is a bit awkward, and it's less efficient than a C loop, since the C compiler can effectively vectorize the loop with optimizations. So this patch moves the loop that initializes the elements to the C side. `allocateMutArrPtrs`/`allocateSmallMutArrPtrs` now takes a new `init` argument and initializes the elements if `init` is non-NULL. - - - - - 7 changed files: - rts/AllocArray.c - rts/AllocArray.h - rts/ClosureTable.c - rts/Heap.c - rts/PrimOps.cmm - rts/Threads.c - rts/Weak.c Changes: ===================================== rts/AllocArray.c ===================================== @@ -5,6 +5,7 @@ StgMutArrPtrs *allocateMutArrPtrs (Capability *cap, StgWord nelements, + StgClosure *init, CostCentreStack *ccs USED_IF_PROFILING) { /* All sizes in words */ @@ -25,6 +26,12 @@ StgMutArrPtrs *allocateMutArrPtrs (Capability *cap, arr->ptrs = nelements; arr->size = arrsize; + if (init != NULL) { + for (StgWord i = 0; i < nelements; ++i) { + arr->payload[i] = init; + } + } + /* Initialize the card array. Note that memset needs sizes in bytes. */ memset(&(arr->payload[nelements]), 0, mutArrPtrsCards(nelements)); @@ -33,6 +40,7 @@ StgMutArrPtrs *allocateMutArrPtrs (Capability *cap, StgSmallMutArrPtrs *allocateSmallMutArrPtrs (Capability *cap, StgWord nelements, + StgClosure *init, CostCentreStack *ccs USED_IF_PROFILING) { @@ -47,6 +55,13 @@ StgSmallMutArrPtrs *allocateSmallMutArrPtrs (Capability *cap, /* No write barrier needed since this is a new allocation. */ SET_HDR(arr, &stg_SMALL_MUT_ARR_PTRS_DIRTY_info, ccs); arr->ptrs = nelements; + + if (init != NULL) { + for (StgWord i = 0; i < nelements; ++i) { + arr->payload[i] = init; + } + } + return arr; } ===================================== rts/AllocArray.h ===================================== @@ -21,16 +21,19 @@ */ /* Allocate a StgMutArrPtrs for a given number of elements. It is allocated in - * the DIRTY state. + * the DIRTY state. If init is non-NULL, initialize payload elements to init. */ StgMutArrPtrs *allocateMutArrPtrs (Capability *cap, StgWord nelements, + StgClosure *init, CostCentreStack *ccs); -/* Allocate a StgSmallMutArrPtrs for a given number of elements. +/* Allocate a StgSmallMutArrPtrs for a given number of elements. If init is + * non-NULL, initialize payload elements to init. */ StgSmallMutArrPtrs *allocateSmallMutArrPtrs (Capability *cap, StgWord nelements, + StgClosure *init, CostCentreStack *ccs); /* Allocate a StgArrBytes for a given number of bytes. ===================================== rts/ClosureTable.c ===================================== @@ -46,7 +46,7 @@ bool enlargeClosureTable(Capability *cap, ClosureTable *t, int newcapacity) ASSERT(newcapacity > oldcapacity); StgMutArrPtrs *newarr; - newarr = allocateMutArrPtrs(cap, newcapacity, CCS_SYSTEM_OR_NULL); + newarr = allocateMutArrPtrs(cap, newcapacity, NULL, CCS_SYSTEM_OR_NULL); if (RTS_UNLIKELY(newarr == NULL)) return false; StgArrBytes *newfree; @@ -276,4 +276,3 @@ static bool isCompactClosureTable(ClosureTable *t) } return isCompact; } - ===================================== rts/Heap.c ===================================== @@ -279,7 +279,7 @@ StgMutArrPtrs *heap_view_closurePtrs(Capability *cap, StgClosure *closure) { StgClosure **ptrs = (StgClosure **) stgMallocBytes(sizeof(StgClosure *) * size, "heap_view_closurePtrs"); StgWord nptrs = collect_pointers(closure, ptrs); - StgMutArrPtrs *arr = allocateMutArrPtrs(cap, nptrs, cap->r.rCCCS); + StgMutArrPtrs *arr = allocateMutArrPtrs(cap, nptrs, NULL, cap->r.rCCCS); if (RTS_UNLIKELY(arr == NULL)) goto end; SET_INFO((StgClosure *) arr, &stg_MUT_ARR_PTRS_FROZEN_CLEAN_info); ===================================== rts/PrimOps.cmm ===================================== @@ -386,24 +386,11 @@ stg_newArrayzh ( W_ n /* words */, gcptr init ) again: MAYBE_GC(again); - ("ptr" arr) = ccall allocateMutArrPtrs(MyCapability() "ptr", n, CCCS); + ("ptr" arr) = ccall allocateMutArrPtrs(MyCapability() "ptr", n, init "ptr", CCCS); if (arr == NULL) (likely: False) { jump stg_raisezh(HsIface_heapOverflow_closure(W_[ghc_hs_iface])); } - // Initialise all elements of the array with the value init - W_ p; - p = arr + SIZEOF_StgMutArrPtrs; - // Avoid the shift for `WDS(n)` in the inner loop - W_ limit; - limit = arr + SIZEOF_StgMutArrPtrs + WDS(n); - for: - if (p < limit) (likely: True) { - W_[p] = init; - p = p + WDS(1); - goto for; - } - return (arr); } @@ -496,24 +483,11 @@ stg_newSmallArrayzh ( W_ n /* words */, gcptr init ) again: MAYBE_GC(again); - ("ptr" arr) = ccall allocateSmallMutArrPtrs(MyCapability() "ptr", n, CCCS); + ("ptr" arr) = ccall allocateSmallMutArrPtrs(MyCapability() "ptr", n, init "ptr", CCCS); if (arr == NULL) (likely: False) { jump stg_raisezh(HsIface_heapOverflow_closure(W_[ghc_hs_iface])); } - // Initialise all elements of the array with the value init - W_ p; - p = arr + SIZEOF_StgSmallMutArrPtrs; - // Avoid the shift for `WDS(n)` in the inner loop - W_ limit; - limit = arr + SIZEOF_StgSmallMutArrPtrs + WDS(n); - for: - if (p < limit) (likely: True) { - W_[p] = init; - p = p + WDS(1); - goto for; - } - return (arr); } ===================================== rts/Threads.c ===================================== @@ -894,7 +894,7 @@ StgMutArrPtrs *listThreads(Capability *cap) } // Allocate a suitably-sized array... - StgMutArrPtrs *arr = allocateMutArrPtrs(cap, n_threads, cap->r.rCCCS); + StgMutArrPtrs *arr = allocateMutArrPtrs(cap, n_threads, NULL, cap->r.rCCCS); if (RTS_UNLIKELY(arr == NULL)) goto end; // Populate it... ===================================== rts/Weak.c ===================================== @@ -146,7 +146,7 @@ scheduleFinalizers(Capability *cap, StgWeak *list) debugTrace(DEBUG_weak, "weak: batching %d finalizers", n); - StgMutArrPtrs *arr = allocateMutArrPtrs(cap, n, CCS_SYSTEM_OR_NULL); + StgMutArrPtrs *arr = allocateMutArrPtrs(cap, n, NULL, CCS_SYSTEM_OR_NULL); if (RTS_UNLIKELY(arr == NULL)) exitHeapOverflow(); // No write barrier needed here; this array is only going to referred to by this core. SET_INFO((StgClosure *) arr, &stg_MUT_ARR_PTRS_FROZEN_CLEAN_info); View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/cdb74049456a5e58c0923bccb08fc8e9... -- View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/cdb74049456a5e58c0923bccb08fc8e9... You're receiving this email because of your account on gitlab.haskell.org.