[stringrefs] Create non-nullable references to strings/views

The string and view creating instructions string.new*, string.const,
string.concat, and string.as_* should all return non-nullable reference
types.

See https://github.com/WebAssembly/stringref/issues/42

Bug: v8:12868
Change-Id: I2a39aadd339a49b4aa2d145492cba85e6ab14b71
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3858236
Commit-Queue: Matthias Liedtke <mliedtke@chromium.org>
Commit-Queue: Jakob Kummerow <jkummerow@chromium.org>
Auto-Submit: Jakob Kummerow <jkummerow@chromium.org>
Reviewed-by: Matthias Liedtke <mliedtke@chromium.org>
Cr-Commit-Position: refs/heads/main@{#82792}

src/wasm/baseline/liftoff-compiler.cc

@@ -6829,6 +6829,10 @@ class LiftoffCompiler {
     __ PushRegister(kRef, result_reg);
   }
 
+  void StringAsWtf16(FullDecoder* decoder, const Value& str, Value* result) {
+    RefAsNonNull(decoder, str, result);
+  }
+
   void StringViewWtf16GetCodeUnit(FullDecoder* decoder, const Value& view,
                                   const Value& pos, Value* result) {
     LiftoffRegList pinned;

src/wasm/function-body-decoder-impl.h

@@ -1134,6 +1134,7 @@ struct ControlBase : public PcForErrors<validate> {
     const Value& bytes, Value* next_pos, Value* bytes_written)                 \
   F(StringViewWtf8Slice, const Value& view, const Value& start,                \
     const Value& end, Value* result)                                           \
+  F(StringAsWtf16, const Value& str, Value* result)                            \
   F(StringViewWtf16GetCodeUnit, const Value& view, const Value& pos,           \
     Value* result)                                                             \
   F(StringViewWtf16Encode, const MemoryIndexImmediate<validate>& memory,       \
@@ -5122,7 +5123,7 @@ class WasmFullDecoder : public WasmDecoder<validate, decoding_mode> {
         ValueType addr_type = this->module_->is_memory64 ? kWasmI64 : kWasmI32;
         Value offset = Peek(1, 0, addr_type);
         Value size = Peek(0, 1, kWasmI32);
-        Value result = CreateValue(kWasmStringRef);
+        Value result = CreateValue(ValueType::Ref(HeapType::kString));
         CALL_INTERFACE_IF_OK_AND_REACHABLE(StringNewWtf8, imm, offset, size,
                                            &result);
         Drop(2);
@@ -5136,7 +5137,7 @@ class WasmFullDecoder : public WasmDecoder<validate, decoding_mode> {
         ValueType addr_type = this->module_->is_memory64 ? kWasmI64 : kWasmI32;
         Value offset = Peek(1, 0, addr_type);
         Value size = Peek(0, 1, kWasmI32);
-        Value result = CreateValue(kWasmStringRef);
+        Value result = CreateValue(ValueType::Ref(HeapType::kString));
         CALL_INTERFACE_IF_OK_AND_REACHABLE(StringNewWtf16, imm, offset, size,
                                            &result);
         Drop(2);
@@ -5146,7 +5147,7 @@ class WasmFullDecoder : public WasmDecoder<validate, decoding_mode> {
       case kExprStringConst: {
         StringConstImmediate<validate> imm(this, this->pc_ + opcode_length);
         if (!this->Validate(this->pc_ + opcode_length, imm)) return 0;
-        Value result = CreateValue(kWasmStringRef);
+        Value result = CreateValue(ValueType::Ref(HeapType::kString));
         CALL_INTERFACE_IF_OK_AND_REACHABLE(StringConst, imm, &result);
         Push(result);
         return opcode_length + imm.length;
@@ -5203,7 +5204,7 @@ class WasmFullDecoder : public WasmDecoder<validate, decoding_mode> {
         NON_CONST_ONLY
         Value head = Peek(1, 0, kWasmStringRef);
         Value tail = Peek(0, 1, kWasmStringRef);
-        Value result = CreateValue(kWasmStringRef);
+        Value result = CreateValue(ValueType::Ref(HeapType::kString));
         CALL_INTERFACE_IF_OK_AND_REACHABLE(StringConcat, head, tail, &result);
         Drop(2);
         Push(result);
@@ -5231,7 +5232,7 @@ class WasmFullDecoder : public WasmDecoder<validate, decoding_mode> {
       case kExprStringAsWtf8: {
         NON_CONST_ONLY
         Value str = Peek(0, 0, kWasmStringRef);
-        Value result = CreateValue(kWasmStringViewWtf8);
+        Value result = CreateValue(ValueType::Ref(HeapType::kStringViewWtf8));
         CALL_INTERFACE_IF_OK_AND_REACHABLE(StringAsWtf8, str, &result);
         Drop(str);
         Push(result);
@@ -5273,7 +5274,7 @@ class WasmFullDecoder : public WasmDecoder<validate, decoding_mode> {
         Value view = Peek(2, 0, kWasmStringViewWtf8);
         Value start = Peek(1, 1, kWasmI32);
         Value end = Peek(0, 2, kWasmI32);
-        Value result = CreateValue(kWasmStringRef);
+        Value result = CreateValue(ValueType::Ref(HeapType::kString));
         CALL_INTERFACE_IF_OK_AND_REACHABLE(StringViewWtf8Slice, view, start,
                                            end, &result);
         Drop(3);
@@ -5283,8 +5284,8 @@ class WasmFullDecoder : public WasmDecoder<validate, decoding_mode> {
       case kExprStringAsWtf16: {
         NON_CONST_ONLY
         Value str = Peek(0, 0, kWasmStringRef);
-        Value result = CreateValue(kWasmStringViewWtf16);
-        CALL_INTERFACE_IF_OK_AND_REACHABLE(Forward, str, &result);
+        Value result = CreateValue(ValueType::Ref(HeapType::kStringViewWtf16));
+        CALL_INTERFACE_IF_OK_AND_REACHABLE(StringAsWtf16, str, &result);
         Drop(str);
         Push(result);
         return opcode_length;
@@ -5330,7 +5331,7 @@ class WasmFullDecoder : public WasmDecoder<validate, decoding_mode> {
         Value view = Peek(2, 0, kWasmStringViewWtf16);
         Value start = Peek(1, 1, kWasmI32);
         Value end = Peek(0, 2, kWasmI32);
-        Value result = CreateValue(kWasmStringRef);
+        Value result = CreateValue(ValueType::Ref(HeapType::kString));
         CALL_INTERFACE_IF_OK_AND_REACHABLE(StringViewWtf16Slice, view, start,
                                            end, &result);
         Drop(3);
@@ -5341,7 +5342,7 @@ class WasmFullDecoder : public WasmDecoder<validate, decoding_mode> {
       case kExprStringAsIter: {
         NON_CONST_ONLY
         Value str = Peek(0, 0, kWasmStringRef);
-        Value result = CreateValue(kWasmStringViewIter);
+        Value result = CreateValue(ValueType::Ref(HeapType::kStringViewIter));
         CALL_INTERFACE_IF_OK_AND_REACHABLE(StringAsIter, str, &result);
         Drop(str);
         Push(result);
@@ -5382,7 +5383,7 @@ class WasmFullDecoder : public WasmDecoder<validate, decoding_mode> {
         NON_CONST_ONLY
         Value view = Peek(1, 0, kWasmStringViewIter);
         Value codepoints = Peek(0, 1, kWasmI32);
-        Value result = CreateValue(kWasmStringRef);
+        Value result = CreateValue(ValueType::Ref(HeapType::kString));
         CALL_INTERFACE_IF_OK_AND_REACHABLE(StringViewIterSlice, view,
                                            codepoints, &result);
         Drop(2);
@@ -5396,7 +5397,7 @@ class WasmFullDecoder : public WasmDecoder<validate, decoding_mode> {
         Value array = PeekPackedArray(2, 0, kWasmI8, WasmArrayAccess::kRead);
         Value start = Peek(1, 1, kWasmI32);
         Value end = Peek(0, 2, kWasmI32);
-        Value result = CreateValue(kWasmStringRef);
+        Value result = CreateValue(ValueType::Ref(HeapType::kString));
         CALL_INTERFACE_IF_OK_AND_REACHABLE(StringNewWtf8Array, imm, array,
                                            start, end, &result);
         Drop(3);
@@ -5409,7 +5410,7 @@ class WasmFullDecoder : public WasmDecoder<validate, decoding_mode> {
         Value array = PeekPackedArray(2, 0, kWasmI16, WasmArrayAccess::kRead);
         Value start = Peek(1, 1, kWasmI32);
         Value end = Peek(0, 2, kWasmI32);
-        Value result = CreateValue(kWasmStringRef);
+        Value result = CreateValue(ValueType::Ref(HeapType::kString));
         CALL_INTERFACE_IF_OK_AND_REACHABLE(StringNewWtf16Array, array, start,
                                            end, &result);
         Drop(3);

src/wasm/graph-builder-interface.cc

@@ -1510,6 +1510,15 @@ class WasmGraphBuildingInterface {
                                end.node, decoder->position()));
   }
 
+  void StringAsWtf16(FullDecoder* decoder, const Value& str, Value* result) {
+    // Since we implement stringview_wtf16 as string, that's the type we'll
+    // use for the Node. (The decoder's Value type must be stringview_wtf16
+    // because static type validation relies on it.)
+    result->node =
+        builder_->SetType(builder_->RefAsNonNull(str.node, decoder->position()),
+                          ValueType::Ref(HeapType::kString));
+  }
+
   void StringViewWtf16GetCodeUnit(FullDecoder* decoder, const Value& view,
                                   const Value& pos, Value* result) {
     result->node = builder_->StringViewWtf16GetCodeUnit(

test/mjsunit/wasm/stringrefs-exec.js

@@ -665,6 +665,12 @@ function makeWtf16TestDataSegment() {
 
   builder.addMemory(1, undefined, true /* exported */, false);
 
+  builder.addFunction("view_from_null", kSig_v_v).exportFunc().addBody([
+    kExprRefNull, kStringRefCode,
+    ...GCInstr(kExprStringAsWtf16),
+    kExprDrop,
+  ]);
+
   builder.addFunction("length", kSig_i_w)
     .exportFunc()
     .addBody([
@@ -816,6 +822,8 @@ function makeWtf16TestDataSegment() {
   assertEquals("oo", instance.exports.slice("foo", 1, 100));
   assertEquals("", instance.exports.slice("foo", 1, 0));
 
+  assertThrows(() => instance.exports.view_from_null(),
+               WebAssembly.RuntimeError, 'dereferencing a null pointer');
   assertThrows(() => instance.exports.length_null(),
                WebAssembly.RuntimeError, "dereferencing a null pointer");
   assertThrows(() => instance.exports.get_codeunit_null(),