[Strings] Fix precomputing of StringEq (WebAssembly#6401)

We incorrectly overrode the string operations in the interpreter's subclasses. But
string operations can be implemented in the topmost class there (as they depend on
no module state), so just implement them there, once, in a proper way.

This fixes StringEq by removing its override, and moves the others to the right
place.

Author: kripken

src/wasm-interpreter.h

@@ -1904,7 +1904,9 @@ class ExpressionRunner : public OverriddenVisitor<SubType, Flow> {
   }
   Flow visitStringMeasure(StringMeasure* curr) {
     // For now we only support JS-style strings.
-    assert(curr->op == StringMeasureWTF16View);
+    if (curr->op != StringMeasureWTF16View) {
+      return Flow(NONCONSTANT_FLOW);
+    }
 
     Flow flow = visit(curr->ref);
     if (flow.breaking()) {
@@ -1917,8 +1919,8 @@ class ExpressionRunner : public OverriddenVisitor<SubType, Flow> {
     }
     return Literal(int32_t(data->values.size()));
   }
-  Flow visitStringEncode(StringEncode* curr) { WASM_UNREACHABLE("unimp"); }
-  Flow visitStringConcat(StringConcat* curr) { WASM_UNREACHABLE("unimp"); }
+  Flow visitStringEncode(StringEncode* curr) { return Flow(NONCONSTANT_FLOW); }
+  Flow visitStringConcat(StringConcat* curr) { return Flow(NONCONSTANT_FLOW); }
   Flow visitStringEq(StringEq* curr) {
     NOTE_ENTER("StringEq");
     Flow flow = visit(curr->left);
@@ -1987,7 +1989,9 @@ class ExpressionRunner : public OverriddenVisitor<SubType, Flow> {
   }
   Flow visitStringAs(StringAs* curr) {
     // For now we only support JS-style strings.
-    assert(curr->op == StringAsWTF16);
+    if (curr->op != StringAsWTF16) {
+      return Flow(NONCONSTANT_FLOW);
+    }
 
     Flow flow = visit(curr->ref);
     if (flow.breaking()) {
@@ -2004,10 +2008,10 @@ class ExpressionRunner : public OverriddenVisitor<SubType, Flow> {
     return Literal(data, curr->type.getHeapType());
   }
   Flow visitStringWTF8Advance(StringWTF8Advance* curr) {
-    WASM_UNREACHABLE("unimp");
+    return Flow(NONCONSTANT_FLOW);
   }
   Flow visitStringWTF16Get(StringWTF16Get* curr) {
-    NOTE_ENTER("StringEq");
+    NOTE_ENTER("StringWTF16Get");
     Flow ref = visit(curr->ref);
     if (ref.breaking()) {
       return ref;
@@ -2028,11 +2032,17 @@ class ExpressionRunner : public OverriddenVisitor<SubType, Flow> {
     }
     return Literal(values[i].geti32());
   }
-  Flow visitStringIterNext(StringIterNext* curr) { WASM_UNREACHABLE("unimp"); }
-  Flow visitStringIterMove(StringIterMove* curr) { WASM_UNREACHABLE("unimp"); }
-  Flow visitStringSliceWTF(StringSliceWTF* curr) { WASM_UNREACHABLE("unimp"); }
+  Flow visitStringIterNext(StringIterNext* curr) {
+    return Flow(NONCONSTANT_FLOW);
+  }
+  Flow visitStringIterMove(StringIterMove* curr) {
+    return Flow(NONCONSTANT_FLOW);
+  }
+  Flow visitStringSliceWTF(StringSliceWTF* curr) {
+    return Flow(NONCONSTANT_FLOW);
+  }
   Flow visitStringSliceIter(StringSliceIter* curr) {
-    WASM_UNREACHABLE("unimp");
+    return Flow(NONCONSTANT_FLOW);
   }
 
   virtual void trap(const char* why) { WASM_UNREACHABLE("unimp"); }
@@ -2369,31 +2379,6 @@ class ConstantExpressionRunner : public ExpressionRunner<SubType> {
     NOTE_ENTER("Rethrow");
     return Flow(NONCONSTANT_FLOW);
   }
-  Flow visitStringMeasure(StringMeasure* curr) {
-    return Flow(NONCONSTANT_FLOW);
-  }
-  Flow visitStringEncode(StringEncode* curr) { return Flow(NONCONSTANT_FLOW); }
-  Flow visitStringConcat(StringConcat* curr) { return Flow(NONCONSTANT_FLOW); }
-  Flow visitStringEq(StringEq* curr) { return Flow(NONCONSTANT_FLOW); }
-  Flow visitStringAs(StringAs* curr) { return Flow(NONCONSTANT_FLOW); }
-  Flow visitStringWTF8Advance(StringWTF8Advance* curr) {
-    return Flow(NONCONSTANT_FLOW);
-  }
-  Flow visitStringWTF16Get(StringWTF16Get* curr) {
-    return Flow(NONCONSTANT_FLOW);
-  }
-  Flow visitStringIterNext(StringIterNext* curr) {
-    return Flow(NONCONSTANT_FLOW);
-  }
-  Flow visitStringIterMove(StringIterMove* curr) {
-    return Flow(NONCONSTANT_FLOW);
-  }
-  Flow visitStringSliceWTF(StringSliceWTF* curr) {
-    return Flow(NONCONSTANT_FLOW);
-  }
-  Flow visitStringSliceIter(StringSliceIter* curr) {
-    return Flow(NONCONSTANT_FLOW);
-  }
   Flow visitRefAs(RefAs* curr) {
     // TODO: Remove this once interpretation is implemented.
     if (curr->op == ExternInternalize || curr->op == ExternExternalize) {

test/lit/passes/precompute-strings.wast

@@ -0,0 +1,26 @@
+;; NOTE: Assertions have been generated by update_lit_checks.py and should not be edited.
+
+;; RUN: wasm-opt %s --precompute --fuzz-exec -all -S -o - | filecheck %s
+
+(module
+ ;; CHECK:      (func $eq-no (type $0) (result i32)
+ ;; CHECK-NEXT:  (i32.const 0)
+ ;; CHECK-NEXT: )
+ (func $eq-no (export "eq-no") (result i32)
+  (string.eq
+   (string.const "ab")
+   (string.const "cdefg")
+  )
+ )
+
+ ;; CHECK:      (func $eq-yes (type $0) (result i32)
+ ;; CHECK-NEXT:  (i32.const 1)
+ ;; CHECK-NEXT: )
+ (func $eq-yes (export "eq-yes") (result i32)
+  (string.eq
+   (string.const "ab")
+   (string.const "ab")
+  )
+ )
+)
+