From 75baceba66de295f366ef0aed365e20f7d06adc8 Mon Sep 17 00:00:00 2001
From: David Sherwood <david.sherwood@arm.com>
Date: Wed, 5 Nov 2025 13:56:22 +0000
Subject: [PATCH] AArch64: Fold movtqb + movzbq into just a movzbq

---
 hphp/runtime/vm/jit/vasm-simplify-arm.cpp | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/hphp/runtime/vm/jit/vasm-simplify-arm.cpp b/hphp/runtime/vm/jit/vasm-simplify-arm.cpp
index cc7c363dba01e..e2b8df38409a9 100644
--- a/hphp/runtime/vm/jit/vasm-simplify-arm.cpp
+++ b/hphp/runtime/vm/jit/vasm-simplify-arm.cpp
@@ -134,6 +134,23 @@ bool simplify(Env& env, const ldimmq& inst, Vlabel b, size_t i) {
 
 ///////////////////////////////////////////////////////////////////////////////
 
+bool simplify(Env& env, const movtqb& inst, Vlabel b, size_t i) {
+  if (env.use_counts[inst.d] != 1)
+    return false;
+
+  if (if_inst<Vinstr::movzbq>(env, b, i + 1, [&](const movzbq& ext) {
+      if (ext.s != inst.d)
+        return false;
+
+      return simplify_impl(env, b, i, [&] (Vout& v) {
+        v << movzbq{Vreg8((Vreg)inst.s), ext.d};
+        return 2;
+      });
+    })) {
+  }
+  return false;
+}
+
 bool simplify(Env& env, const movzbl& inst, Vlabel b, size_t i) {
   // movzbl{s, d}; shrli{2, s, d} --> ubfmli{2, 7, s, d}
   return if_inst<Vinstr::shrli>(env, b, i + 1, [&](const shrli& sh) {