StringLowering: Start to lower instructions

src/passes/StringLowering.cpp

@@ -191,6 +191,9 @@ struct StringLowering : public StringGathering {
     // Remove all HeapType::string etc. in favor of externref.
     updateTypes(module);
 
+    // Replace string.* etc. operations with imported ones.
+    replaceInstructions(module);
+
     // Disable the feature here after we lowered everything away.
     module->features.disable(FeatureSet::Strings);
   }
@@ -225,9 +228,88 @@ struct StringLowering : public StringGathering {
 
   void updateTypes(Module* module) {
     TypeMapper::TypeUpdates updates;
+    // There is no difference between strings and views with imported strings:
+    // they are all just JS strings, so they all turn into externref.
     updates[HeapType::string] = HeapType::ext;
+    updates[HeapType::stringview_wtf8] = HeapType::ext;
+    updates[HeapType::stringview_wtf16] = HeapType::ext;
+    updates[HeapType::stringview_iter] = HeapType::ext;
     TypeMapper(*module, updates).map();
   }
+
+  // Imported string functions.
+  Name fromCharCodeArrayImport;
+  Name fromCodePointImport;
+
+  // The name of the module to import string functions from.
+  Name WasmStringsModule = "wasm:js-string";
+
+  // Common types used in imports.
+  auto nullArray16 = Type(Array(Field(Field::i16, Mutable)), Nullable);
+  Type nnExt = Type(HeapType::ext, NonNullable);
+
+  // Creates an imported string function, returning its name (which is equal to
+  // the true name of the import, if there is no conflict).
+  Name addImport(Module* module, Name trueName, Type params, Type results) {
+    auto name = Names::getValidFunctionName(*module, trueName);
+    auto sig = Signature(params, results);
+    Builder builder(*module);
+    auto* func = module->addFunction(builder.makeFunction(name, sig, {}));
+    func->module = WasmStringsModule;
+    func->base = trueName;
+    return name;
+  }
+
+  void replaceInstructions(Module* module) {
+    // Add all the possible imports up front, to avoid adding them during
+    // parallel work. Optimizations can remove unneeded ones later.
+
+    // string.fromCharCodeArray: array, start, end -> ext
+    fromCharCodeArrayImport = addImport(
+      module, "fromCharCodeArray", {nullArray16, Type::i32, Type::i32}, nnExt);
+    // string.fromCodePoint: codepoint -> ext
+    fromCodePointImport = addImport(module, "fromCodePoint", Type::i32, nnExt);
+
+    // Replace the string instructions in parallel.
+    struct Replacer : public WalkerPass<PostWalker<Replacer>> {
+      bool isFunctionParallel() override { return true; }
+
+      StringLowering& lowering;
+
+      std::unique_ptr<Pass> create() override {
+        return std::make_unique<Replacer>(lowering);
+      }
+
+      Replacer(StringLowering& lowering) : lowering(lowering) {}
+
+      void visitStringNew(StringNew* curr) {
+        Builder builder(*getModule());
+        switch (curr->op) {
+          case StringNewWTF16Array:
+            replaceCurrent(builder.makeCall(lowering.fromCharCodeArrayImport,
+                                            {curr->ptr, curr->start, curr->end},
+                                            lowering.nnExt));
+            return;
+          case StringNewFromCodePoint:
+            replaceCurrent(builder.makeCall(
+              lowering.fromCodePointImport, {curr->ptr}, lowering.nnExt));
+            return;
+          default:
+            WASM_UNREACHABLE("TODO: all of string.new*");
+        }
+      }
+
+      void visitStringAs(StringAs* curr) {
+        // There is no difference between strings and views with imported
+        // strings: they are all just JS strings, so no conversion is needed.
+        replaceCurrent(curr->ref);
+      }
+    };
+
+    Replacer replacer(*this);
+    replacer.run(getPassRunner(), module);
+    replacer.walkModuleCode(module);
+  }
 };
 
 Pass* createStringGatheringPass() { return new StringGathering(); }

test/lit/passes/string-gathering.wast

@@ -27,12 +27,22 @@
   ;; CHECK:      (global $global2 stringref (global.get $string.const_bar))
   ;; LOWER:      (type $0 (func))
 
+  ;; LOWER:      (type $1 (array (mut i16)))
+
+  ;; LOWER:      (type $2 (func (param (ref null $1) i32 i32) (result (ref extern))))
+
+  ;; LOWER:      (type $3 (func (param i32) (result (ref extern))))
+
   ;; LOWER:      (import "string.const" "0" (global $string.const_bar (ref extern)))
 
   ;; LOWER:      (import "string.const" "1" (global $string.const_other (ref extern)))
 
   ;; LOWER:      (import "string.const" "2" (global $global (ref extern)))
 
+  ;; LOWER:      (import "wasm:js-string" "fromCharCodeArray" (func $fromCharCodeArray (type $2) (param (ref null $1) i32 i32) (result (ref extern))))
+
+  ;; LOWER:      (import "wasm:js-string" "fromCodePoint" (func $fromCodePoint (type $3) (param i32) (result (ref extern))))
+
   ;; LOWER:      (global $global2 externref (global.get $string.const_bar))
   (global $global2 (ref null string) (string.const "bar"))
 
@@ -111,6 +121,12 @@
 ;; Multiple possible reusable globals. Also test ignoring of imports.
 (module
   ;; CHECK:      (import "a" "b" (global $import (ref string)))
+  ;; LOWER:      (type $0 (array (mut i16)))
+
+  ;; LOWER:      (type $1 (func (param (ref null $0) i32 i32) (result (ref extern))))
+
+  ;; LOWER:      (type $2 (func (param i32) (result (ref extern))))
+
   ;; LOWER:      (import "a" "b" (global $import (ref extern)))
   (import "a" "b" (global $import (ref string)))
 
@@ -122,6 +138,10 @@
 
   ;; LOWER:      (import "string.const" "1" (global $global4 (ref extern)))
 
+  ;; LOWER:      (import "wasm:js-string" "fromCharCodeArray" (func $fromCharCodeArray (type $1) (param (ref null $0) i32 i32) (result (ref extern))))
+
+  ;; LOWER:      (import "wasm:js-string" "fromCodePoint" (func $fromCodePoint (type $2) (param i32) (result (ref extern))))
+
   ;; LOWER:      (global $global2 (ref extern) (global.get $global1))
   (global $global2 (ref string) (string.const "foo"))
 

test/lit/passes/string-lowering-instructions.wast

@@ -0,0 +1,95 @@
+;; NOTE: Assertions have been generated by update_lit_checks.py --all-items and should not be edited.
+
+;; RUN: foreach %s %t wasm-opt --string-lowering  -all -S -o - | filecheck %s
+
+(module
+  ;; CHECK:      (type $0 (func))
+
+  ;; CHECK:      (type $array16 (array (mut i16)))
+  (type $array16 (array (mut i16)))
+
+  ;; CHECK:      (rec
+  ;; CHECK-NEXT:  (type $2 (func (param (ref $array16))))
+
+  ;; CHECK:       (type $3 (func (param externref externref externref externref)))
+
+  ;; CHECK:      (type $4 (func (param (ref null $array16) i32 i32) (result (ref extern))))
+
+  ;; CHECK:      (type $5 (func (param i32) (result (ref extern))))
+
+  ;; CHECK:      (import "colliding" "name" (func $fromCodePoint (type $0)))
+  (import "colliding" "name" (func $fromCodePoint))
+
+  ;; CHECK:      (import "wasm:js-string" "fromCharCodeArray" (func $fromCharCodeArray (type $4) (param (ref null $array16) i32 i32) (result (ref extern))))
+
+  ;; CHECK:      (import "wasm:js-string" "fromCodePoint" (func $fromCodePoint_5 (type $5) (param i32) (result (ref extern))))
+
+  ;; CHECK:      (func $string.as (type $3) (param $a externref) (param $b externref) (param $c externref) (param $d externref)
+  ;; CHECK-NEXT:  (local.set $b
+  ;; CHECK-NEXT:   (local.get $a)
+  ;; CHECK-NEXT:  )
+  ;; CHECK-NEXT:  (local.set $c
+  ;; CHECK-NEXT:   (local.get $a)
+  ;; CHECK-NEXT:  )
+  ;; CHECK-NEXT:  (local.set $d
+  ;; CHECK-NEXT:   (local.get $a)
+  ;; CHECK-NEXT:  )
+  ;; CHECK-NEXT: )
+  (func $string.as
+    (param $a stringref)
+    (param $b stringview_wtf8)
+    (param $c stringview_wtf16)
+    (param $d stringview_iter)
+    ;; These operations all vanish in the lowering, as they all become extref
+    ;; (JS strings).
+    (local.set $b
+      (string.as_wtf8
+        (local.get $a)
+      )
+    )
+    (local.set $c
+      (string.as_wtf16
+        (local.get $a)
+      )
+    )
+    (local.set $d
+      (string.as_iter
+        (local.get $a)
+      )
+    )
+  )
+
+  ;; CHECK:      (func $string.new.gc (type $2) (param $array16 (ref $array16))
+  ;; CHECK-NEXT:  (drop
+  ;; CHECK-NEXT:   (call $fromCharCodeArray
+  ;; CHECK-NEXT:    (local.get $array16)
+  ;; CHECK-NEXT:    (i32.const 7)
+  ;; CHECK-NEXT:    (i32.const 8)
+  ;; CHECK-NEXT:   )
+  ;; CHECK-NEXT:  )
+  ;; CHECK-NEXT: )
+  (func $string.new.gc (param $array16 (ref $array16))
+    (drop
+      (string.new_wtf16_array
+        (local.get $array16)
+        (i32.const 7)
+        (i32.const 8)
+      )
+    )
+  )
+
+  ;; CHECK:      (func $string.from_code_point (type $0)
+  ;; CHECK-NEXT:  (drop
+  ;; CHECK-NEXT:   (call $fromCodePoint_5
+  ;; CHECK-NEXT:    (i32.const 1)
+  ;; CHECK-NEXT:   )
+  ;; CHECK-NEXT:  )
+  ;; CHECK-NEXT: )
+  (func $string.from_code_point
+    (drop
+      (string.from_code_point
+        (i32.const 1)
+      )
+    )
+  )
+)