JIT: Stop setting class handles for promoted parameter SIMD fields (#87967)

Having these class handles floating around in the JIT is problematic
during prejit where the JIT-EE calls allowed on "random" type handles
(in this case the type of a field of a struct) is limited.

Precursor to #87917

Author: jakobbotsch

src/coreclr/jit/codegencommon.cpp

@@ -3017,7 +3017,20 @@ void CodeGen::genFnPrologCalleeRegArgs(regNumber xtraReg, bool* pXtraRegClobbere
 #if defined(UNIX_AMD64_ABI)
         if (varTypeIsStruct(varDsc))
         {
-            CORINFO_CLASS_HANDLE typeHnd = varDsc->GetLayout()->GetClassHandle();
+            CORINFO_CLASS_HANDLE typeHnd;
+            if (varDsc->lvIsStructField)
+            {
+                // The only case we currently permit is a wrapped SIMD field,
+                // where we won't have the class handle available, so get it
+                // from the parent struct -- they will agree on ABI details.
+                LclVarDsc* parentDsc = compiler->lvaGetDesc(varDsc->lvParentLcl);
+                assert(varTypeIsSIMD(varDsc) && (parentDsc->lvFieldCnt == 1));
+                typeHnd = parentDsc->GetLayout()->GetClassHandle();
+            }
+            else
+            {
+                typeHnd = varDsc->GetLayout()->GetClassHandle();
+            }
             assert(typeHnd != nullptr);
             SYSTEMV_AMD64_CORINFO_STRUCT_REG_PASSING_DESCRIPTOR structDesc;
             compiler->eeGetSystemVAmd64PassStructInRegisterDescriptor(typeHnd, &structDesc);
@@ -3114,7 +3127,7 @@ void CodeGen::genFnPrologCalleeRegArgs(regNumber xtraReg, bool* pXtraRegClobbere
                 }
             }
 #if FEATURE_MULTIREG_ARGS
-            else if (compiler->lvaIsMultiregStruct(varDsc, compiler->info.compIsVarArgs))
+            else if (varDsc->lvIsMultiRegArg)
             {
                 if (varDsc->lvIsHfaRegArg())
                 {
@@ -3323,7 +3336,7 @@ void CodeGen::genFnPrologCalleeRegArgs(regNumber xtraReg, bool* pXtraRegClobbere
                 {
                     // This must be a SIMD type that's fully enregistered, but is passed as an HFA.
                     // Each field will be inserted into the same destination register.
-                    assert(varTypeIsSIMD(varDsc) && !compiler->isOpaqueSIMDType(varDsc->GetLayout()));
+                    assert(varTypeIsSIMD(varDsc));
                     assert(regArgTab[argNum].slot <= (int)varDsc->lvHfaSlots());
                     assert(argNum > 0);
                     assert(regArgTab[argNum - 1].varNum == varNum);

src/coreclr/jit/lclvars.cpp

@@ -2523,10 +2523,23 @@ void Compiler::StructPromotionHelper::PromoteStructVar(unsigned lclNum)
 #ifdef FEATURE_SIMD
         if (varTypeIsSIMD(pFieldInfo->fldType))
         {
-            compiler->lvaSetStruct(varNum, pFieldInfo->fldTypeHnd, false);
             // We will not recursively promote this, so mark it as 'lvRegStruct' (note that we wouldn't
             // be promoting this if we didn't think it could be enregistered.
             fieldVarDsc->lvRegStruct = true;
+
+            // SIMD types may be HFAs so we need to set the correct state on
+            // the promoted fields to get the right ABI treatment in the
+            // backend.
+            if (GlobalJitOptions::compFeatureHfa && (pFieldInfo->fldSize <= MAX_PASS_MULTIREG_BYTES))
+            {
+                // hfaType is set to float, double or SIMD type if it is an HFA, otherwise TYP_UNDEF
+                var_types hfaType = compiler->GetHfaType(pFieldInfo->fldTypeHnd);
+                if (varTypeIsValidHfaType(hfaType))
+                {
+                    fieldVarDsc->SetHfaType(hfaType);
+                    fieldVarDsc->lvIsMultiRegArg = (varDsc->lvIsMultiRegArg != 0) && (fieldVarDsc->lvHfaSlots() > 1);
+                }
+            }
         }
 #endif // FEATURE_SIMD
 
@@ -2986,16 +2999,20 @@ void Compiler::lvaSetStruct(unsigned varNum, ClassLayout* layout, bool unsafeVal
         }
 #endif // not TARGET_64BIT
 
-        unsigned classAttribs = info.compCompHnd->getClassAttribs(layout->GetClassHandle());
-
         // Check whether this local is an unsafe value type and requires GS cookie protection.
         // GS checks require the stack to be re-ordered, which can't be done with EnC.
-        if (unsafeValueClsCheck && (classAttribs & CORINFO_FLG_UNSAFE_VALUECLASS) && !opts.compDbgEnC)
+        if (unsafeValueClsCheck)
         {
-            setNeedsGSSecurityCookie();
-            compGSReorderStackLayout = true;
-            varDsc->lvIsUnsafeBuffer = true;
+            unsigned classAttribs = info.compCompHnd->getClassAttribs(layout->GetClassHandle());
+
+            if ((classAttribs & CORINFO_FLG_UNSAFE_VALUECLASS) && !opts.compDbgEnC)
+            {
+                setNeedsGSSecurityCookie();
+                compGSReorderStackLayout = true;
+                varDsc->lvIsUnsafeBuffer = true;
+            }
         }
+
 #ifdef DEBUG
         if (JitConfig.EnableExtraSuperPmiQueries())
         {

src/coreclr/jit/regalloc.cpp

@@ -154,7 +154,7 @@ regNumber Compiler::raUpdateRegStateForArg(RegState* regState, LclVarDsc* argDsc
         if (argDsc->lvIsHfaRegArg())
         {
             assert(regState->rsIsFloat);
-            unsigned cSlots = GetHfaCount(argDsc->GetLayout()->GetClassHandle());
+            unsigned cSlots = argDsc->lvHfaSlots();
             for (unsigned i = 1; i < cSlots; i++)
             {
                 assert(inArgReg + i <= LAST_FP_ARGREG);