Fix struct promotion check for SIMD field (dotnet/coreclr#18548)

A struct can have `lvIsRegArg` true but have multiple SIMD fields if it is passed by reference.

Commit migrated from https://github.com/dotnet/coreclr/commit/d3905518d08ca174ae631aebfe16314b885aa61a

diff --git a/src/coreclr/src/jit/lclvars.cpp b/src/coreclr/src/jit/lclvars.cpp
index e0e8f74..b36fcad 100644 (file)
--- a/src/coreclr/src/jit/lclvars.cpp
+++ b/src/coreclr/src/jit/lclvars.cpp
@@ -2011,7 +2011,7 @@ void Compiler::lvaPromoteStructVar(unsigned lclNum, lvaStructPromotionInfo* Stru
             fieldVarDsc->lvArgReg   = varDsc->lvArgReg;
             fieldVarDsc->setPrefReg(varDsc->lvArgReg, this); // Set the preferred register
 #if FEATURE_MULTIREG_ARGS && defined(FEATURE_SIMD)
-            if (varTypeIsSIMD(fieldVarDsc))
+            if (varTypeIsSIMD(fieldVarDsc) && !lvaIsImplicitByRefLocal(lclNum))
             {
                 // This field is a SIMD type, and will be considered to be passed in multiple registers
                 // if the parent struct was. Note that this code relies on the fact that if there is