From c0ca9581eceff89e992430f379a82fe26a267a4f Mon Sep 17 00:00:00 2001
From: Sergey Andreenko <seandree@microsoft.com>
Date: Tue, 5 Jan 2021 17:58:46 -0800
Subject: [PATCH] Fix `assert(isByteReg(ireg))`. (#46567)

---
 src/coreclr/jit/lsrabuild.cpp | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/src/coreclr/jit/lsrabuild.cpp b/src/coreclr/jit/lsrabuild.cpp
index ac383e5..06b6799 100644
--- a/src/coreclr/jit/lsrabuild.cpp
+++ b/src/coreclr/jit/lsrabuild.cpp
@@ -3273,11 +3273,20 @@ int LinearScan::BuildMultiRegStoreLoc(GenTreeLclVar* storeLoc)
     //
     for (unsigned int i = 0; i < dstCount; ++i)
     {
+        LclVarDsc* fieldVarDsc = compiler->lvaGetDesc(varDsc->lvFieldLclStart + i);
+
         if (isMultiRegSrc)
         {
-            BuildUse(op1, RBM_NONE, i);
+            regMaskTP srcCandidates = RBM_NONE;
+#ifdef TARGET_X86
+            var_types type = fieldVarDsc->TypeGet();
+            if (varTypeIsByte(type))
+            {
+                srcCandidates = allByteRegs();
+            }
+#endif // TARGET_X86
+            BuildUse(op1, srcCandidates, i);
         }
-        LclVarDsc* fieldVarDsc = compiler->lvaGetDesc(varDsc->lvFieldLclStart + i);
         assert(isCandidateVar(fieldVarDsc));
         BuildStoreLocDef(storeLoc, fieldVarDsc, nullptr, i);
         if (isMultiRegSrc && (i < (dstCount - 1)))
-- 
2.7.4