From 63eb1990e45434e5e294c7a3d32f7f7d9719ac60 Mon Sep 17 00:00:00 2001
From: Aakash Patel <avp@meta.com>
Date: Wed, 28 Aug 2024 07:58:30 -0700
Subject: [PATCH] Add GetByIndex in native backend

Reviewed By: tmikov

Differential Revision: D61743977

fbshipit-source-id: 71c8e14ed13a70238774f2ef1fb9dc4bb871d1f6
---
 include/hermes/VM/static_h.h |  2 ++
 lib/BCGen/SH/SH.cpp          |  9 +++++++++
 lib/VM/StaticH.cpp           | 33 +++++++++++++++++++++++++++++++++
 3 files changed, 44 insertions(+)

diff --git a/include/hermes/VM/static_h.h b/include/hermes/VM/static_h.h
index 0f57cfd1666..29153d8ff31 100644
--- a/include/hermes/VM/static_h.h
+++ b/include/hermes/VM/static_h.h
@@ -499,6 +499,8 @@ SHERMES_EXPORT SHLegacyValue _sh_ljs_get_by_val_rjs(
     SHRuntime *shr,
     SHLegacyValue *source,
     SHLegacyValue *key);
+SHERMES_EXPORT SHLegacyValue
+_sh_ljs_get_by_index_rjs(SHRuntime *shr, SHLegacyValue *source, uint8_t key);
 
 /// Put an enumerable property.
 SHERMES_EXPORT void _sh_ljs_put_own_by_val(
diff --git a/lib/BCGen/SH/SH.cpp b/lib/BCGen/SH/SH.cpp
index bf820ae9132..1108d6673e4 100644
--- a/lib/BCGen/SH/SH.cpp
+++ b/lib/BCGen/SH/SH.cpp
@@ -1298,6 +1298,15 @@ class InstrGen {
       genStringConstIC(LS) << ");\n";
       return;
     }
+    // If the prop is a uint8_t constant, generate the special bytecode.
+    if (auto *litNum = llvh::dyn_cast<LiteralNumber>(inst.getProperty());
+        litNum && litNum->isUInt8Representible()) {
+      os_ << "_sh_ljs_get_by_index_rjs(shr,&";
+      generateRegister(*inst.getObject());
+      os_ << ", ";
+      os_ << litNum->asUInt8() << ");\n";
+      return;
+    }
     os_ << "_sh_ljs_get_by_val_rjs(shr,&";
     generateRegister(*inst.getObject());
     os_ << ", &";
diff --git a/lib/VM/StaticH.cpp b/lib/VM/StaticH.cpp
index 17cdebe3199..f9db2cfb7ff 100644
--- a/lib/VM/StaticH.cpp
+++ b/lib/VM/StaticH.cpp
@@ -310,6 +310,39 @@ extern "C" SHLegacyValue _sh_ljs_get_by_val_rjs(
   return res->getHermesValue();
 }
 
+extern "C" SHLegacyValue
+_sh_ljs_get_by_index_rjs(SHRuntime *shr, SHLegacyValue *source, uint8_t key) {
+  Handle<> sourceHandle{toPHV(source)};
+  Runtime &runtime = getRuntime(shr);
+  if (LLVM_LIKELY(sourceHandle->isObject())) {
+    Handle<JSObject> objHandle = Handle<JSObject>::vmcast(sourceHandle);
+    if (LLVM_LIKELY(objHandle->hasFastIndexProperties())) {
+      auto ourValue = createPseudoHandle(JSObject::getOwnIndexed(
+          createPseudoHandle(*objHandle), runtime, key));
+      if (LLVM_LIKELY(!ourValue->isEmpty())) {
+        return ourValue.getHermesValue();
+      }
+    }
+  }
+
+  // Otherwise...
+  // This is the "slow path".
+  auto res = [&]() {
+    struct : public Locals {
+      PinnedValue<> key;
+    } lv;
+    LocalsRAII lraii{runtime, &lv};
+
+    lv.key = HermesValue::encodeTrustedNumberValue(key);
+    return Interpreter::getByValTransient_RJS(runtime, sourceHandle, lv.key);
+  }();
+
+  if (LLVM_UNLIKELY(res == ExecutionStatus::EXCEPTION)) {
+    _sh_throw_current(shr);
+  }
+  return res->getHermesValue();
+}
+
 extern "C" SHLegacyValue _sh_catch(
     SHRuntime *shr,
     SHLocals *locals,