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Ben Gamari pushed to branch wip/T26009 at Glasgow Haskell Compiler / GHC

Commits:

827961b9

by Ben Gamari at 2025-05-19T16:01:12-04:00

rts/Hash: Factor out hashBuffer

This is a useful helper which can be used for non-strings as well.

deadc2ef

by Ben Gamari at 2025-05-19T16:01:24-04:00

rts/linker/PEi386: Don't repeated load DLLs

Previously every DLL-imported symbol would result in a call to
`LoadLibraryEx`. This ended up constituting over 40% of the runtime of
`ghc --interactive -e 42` on Windows. Avoid this by maintaining a
hash-set of loaded DLL names, skipping the call if we have already
loaded the requested DLL.

Addresses #26009.

3 changed files:

rts/Hash.c
rts/Hash.h
rts/linker/PEi386.c

Changes:

rts/Hash.c

@@ -94,13 +94,13 @@ hashWord(const HashTable *table, StgWord key)
+ }
  int
 -hashStr(const HashTable *table, StgWord w)
 +hashBuffer(const HashTable *table, const void *buf, size_t len)
+ {
 -    const char *key = (char*) w;
 +    const char *key = (char*) buf;
  #if WORD_SIZE_IN_BITS == 64
 -    StgWord h = XXH3_64bits_withSeed (key, strlen(key), 1048583);
 +    StgWord h = XXH3_64bits_withSeed (key, len, 1048583);
  #else
 -    StgWord h = XXH32 (key, strlen(key), 1048583);
 +    StgWord h = XXH32 (key, len, 1048583);
  #endif
      /* Mod the size of the hash table (a power of 2) */
@@ -114,6 +114,13 @@ hashStr(const HashTable *table, StgWord w)
      return bucket;
+ }
 +int
 +hashStr(const HashTable *table, StgWord w)
 +{
 +    const char *key = (char*) w;
 +    return hashBuffer(table, key, strlen(key));
 +}
++
  STATIC_INLINE int
  compareWord(StgWord key1, StgWord key2)
+ {

rts/Hash.h

@@ -69,6 +69,10 @@ void *      removeStrHashTable ( StrHashTable *table, const char * key,
   */
  typedef int HashFunction(const HashTable *table, StgWord key);
  typedef int CompareFunction(StgWord key1, StgWord key2);
++
 +// Helper for implementing hash functions
 +int hashBuffer(const HashTable *table, const void *buf, size_t len);
++
  int hashWord(const HashTable *table, StgWord key);
  int hashStr(const HashTable *table, StgWord w);
  void        insertHashTable_ ( HashTable *table, StgWord key,
@@ -79,6 +83,7 @@ void *      removeHashTable_ ( HashTable *table, StgWord key,
                                 const void *data, HashFunction f,
                                 CompareFunction cmp );
++
  /* Freeing hash tables
   */
  void freeHashTable ( HashTable *table, void (*freeDataFun)(void *) );

rts/linker/PEi386.c

@@ -427,8 +427,53 @@ const int default_alignment = 8;
     the pointer as a redirect.  Essentially it's a DATA DLL reference.  */
  const void* __rts_iob_func = (void*)&__acrt_iob_func;
 +/*
 + * Note [Avoiding repeated DLL loading]
 + * ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 + * As LoadLibraryEx tends to be expensive and addDLL_PEi386 is called on every
 + * DLL-imported symbol, we use a hash-set to keep track of which DLLs have
 + * already been loaded. This hash-set is keyed on the dll_name passed to
 + * addDLL_PEi386 and serves as a quick check to avoid repeated calls to
 + * LoadLibraryEx for the identical DLL. See #26009.
 + */
++
 +typedef struct {
 +    HashTable *hash;
 +} LoadedDllSet;
++
 +LoadedDllSet loaded_dll_set;
++
 +void initLoadedDllSet(LoadedDllSet *set) {
 +    set->hash = allocHashTable();
 +}
++
 +int hash_path(const HashTable *table, StgWord w)
 +{
 +    const pathchar *key = (pathchar*) w;
 +    return hashBuffer(table, key, sizeof(pathchar) * wcslen(key));
 +}
++
 +int compare_path(StgWord key1, StgWord key2)
 +{
 +    return wscmp((pathchar*) key1, (pathchar*) key2);
 +}
++
 +void addLoadedDll(LoadedDllSet *set, pathchar *dll_name)
 +{
 +    insertHashTable_(set->hash, (StgWord) dll_name, (void*) 1, hash_path);
 +}
++
 +bool isDllLoaded(LoadedDllSet *set, pathchar *dll_name)
 +{
 +    void * result = lookupHashTable_(set->hash, (StgWord) dll_name, hash_path, compare_path);
 +    return result != NULL;
 +}
++
++
  void initLinker_PEi386(void)
+ {
 +    initLoadedDllSet(&loaded_dll_set);
++
      if (!ghciInsertSymbolTable(WSTR("(GHCi/Ld special symbols)"),
                                 symhash, "__image_base__",
                                 GetModuleHandleW (NULL), HS_BOOL_TRUE,
@@ -802,6 +847,10 @@ addDLL_PEi386( pathchar *dll_name, HINSTANCE *loaded )
      /* ------------------- Win32 DLL loader ------------------- */
      IF_DEBUG(linker, debugBelch("addDLL; dll_name = `%" PATH_FMT "'\n", dll_name));
 +    if (isDllLoaded(&loaded_dll_set, dll_name)) {
 +        return NULL;
 +    }
++
      /* The file name has no suffix (yet) so that we can try
         both foo.dll and foo.drv
@@ -840,6 +889,7 @@ addDLL_PEi386( pathchar *dll_name, HINSTANCE *loaded )
          goto error;
+     }
 +    addLoadedDll(&loaded_dll_set, dll_name);
      addDLLHandle(buf, instance);
      if (loaded) {
          *loaded = instance;