[Strings] Fix StringSlice end computation (#6414)

Like JS string slicing, if the end index is out of bounds that is fine, we clamp to the end.

This also matches the behavior in V8 and the spec.

Author: kripken

src/wasm-interpreter.h

@@ -1986,6 +1986,7 @@ class ExpressionRunner : public OverriddenVisitor<SubType, Flow> {
     if (ref.breaking()) {
       return ref;
     }
+    // TODO: "WTF-16 position treatment", as in stringview_wtf16.slice?
     Flow ptr = visit(curr->ptr);
     if (ptr.breaking()) {
       return ptr;
@@ -2173,9 +2174,7 @@ class ExpressionRunner : public OverriddenVisitor<SubType, Flow> {
     auto& refValues = refData->values;
     auto startVal = start.getSingleValue().getUnsigned();
     auto endVal = end.getSingleValue().getUnsigned();
-    if (endVal > refValues.size()) {
-      trap("array oob");
-    }
+    endVal = std::min<size_t>(endVal, refValues.size());
     if (hasNonAsciiUpTo(refValues, endVal)) {
       return Flow(NONCONSTANT_FLOW);
     }

test/lit/exec/strings.wast

@@ -255,6 +255,17 @@
       (i32.const 6)
     )
   )
+
+  ;; CHECK:      [fuzz-exec] calling slice-big
+  ;; CHECK-NEXT: [fuzz-exec] note result: slice-big => string("defgh")
+  (func $slice-big (export "slice-big") (result (ref string))
+    ;; Slicing [3:huge unsigned value] leads to slicing til the end: "defgh".
+    (stringview_wtf16.slice
+      (string.const "abcdefgh")
+      (i32.const 3)
+      (i32.const -1)
+    )
+  )
 )
 ;; CHECK:      [fuzz-exec] calling new_wtf16_array
 ;; CHECK-NEXT: [fuzz-exec] note result: new_wtf16_array => string("ello")
@@ -323,6 +334,9 @@
 
 ;; CHECK:      [fuzz-exec] calling slice
 ;; CHECK-NEXT: [fuzz-exec] note result: slice => string("def")
+
+;; CHECK:      [fuzz-exec] calling slice-big
+;; CHECK-NEXT: [fuzz-exec] note result: slice-big => string("defgh")
 ;; CHECK-NEXT: [fuzz-exec] comparing compare.1
 ;; CHECK-NEXT: [fuzz-exec] comparing compare.10
 ;; CHECK-NEXT: [fuzz-exec] comparing compare.2
@@ -344,3 +358,4 @@
 ;; CHECK-NEXT: [fuzz-exec] comparing get_length
 ;; CHECK-NEXT: [fuzz-exec] comparing new_wtf16_array
 ;; CHECK-NEXT: [fuzz-exec] comparing slice
+;; CHECK-NEXT: [fuzz-exec] comparing slice-big