Armel support in crossgen2 (#43706)

This change adds support for armel target compilation in crossgen2

To use the feature compile an application using the --targetos Linux and --targetarch armel flags.

Summary of changes
- To avoid bloating the compilation matrix, the #ifdefs used in the JIT that were conditional on ARM_SOFTFP behavior have been changed in to variable checks. To avoid perf penalties, this dynamic behavior is only enabled for the jit intended for compiling using crossgen2.
- Armel abi processing was integrated into the various parts of the managed crossgen2 codebase that correspond to components with special handling in the coreclr codebase
  - HFA support is disabled for Armel targets
  - Floating point registers are not used when passing arguments

With this change it becomes possible to run crossgen2 on a Windows or Linux machine and target a Linux Armel target.

Author: davidwrighton

src/coreclr/inc/corjitflags.h

@@ -97,7 +97,12 @@ class CORJIT_FLAGS
 
         CORJIT_FLAG_NO_INLINING             = 42, // JIT should not inline any called method into this method
 
+#if defined(TARGET_ARM)
+        CORJIT_FLAG_SOFTFP_ABI              = 43, // JIT should generate PC-relative address computations instead of EE relocation records
+#else // !defined(TARGET_ARM)
         CORJIT_FLAG_UNUSED16                = 43,
+#endif // !defined(TARGET_ARM)
+
         CORJIT_FLAG_UNUSED17                = 44,
         CORJIT_FLAG_UNUSED18                = 45,
         CORJIT_FLAG_UNUSED19                = 46,

src/coreclr/inc/switches.h

@@ -150,7 +150,7 @@
 // do not work reliably with conservative GC.
 #define FEATURE_CONSERVATIVE_GC 1
 
-#if (defined(TARGET_ARM) && !defined(ARM_SOFTFP)) || defined(TARGET_ARM64)
+#if (defined(TARGET_ARM) && (!defined(ARM_SOFTFP) || defined(CONFIGURABLE_ARM_ABI))) || defined(TARGET_ARM64)
 #define FEATURE_HFA
 #endif
 

src/coreclr/jit/CMakeLists.txt

@@ -490,6 +490,7 @@ if (CLR_CMAKE_BUILD_SUBSET_ALLJITS AND NOT CLR_CROSS_COMPONENTS_BUILD)
 
   create_standalone_jit(TARGET clrjit_unix_armel_${ARCH_HOST_NAME} OS unix ARCH armel)
   create_standalone_jit(TARGET clrjit_unix_arm_${ARCH_HOST_NAME} OS unix ARCH arm)
+  target_compile_definitions(clrjit_unix_arm_${ARCH_HOST_NAME} PRIVATE ARM_SOFTFP CONFIGURABLE_ARM_ABI)
   create_standalone_jit(TARGET clrjit_win_arm_${ARCH_HOST_NAME} OS win ARCH arm)
   create_standalone_jit(TARGET clrjit_win_x86_${ARCH_HOST_NAME} OS win ARCH x86)
 else()

src/coreclr/jit/codegencommon.cpp

@@ -4004,40 +4004,38 @@ void CodeGen::genFnPrologCalleeRegArgs(regNumber xtraReg, bool* pXtraRegClobbere
 
         if (doingFloat)
         {
-#if defined(FEATURE_HFA) || defined(UNIX_AMD64_ABI)
-            insCopy = ins_Copy(TYP_DOUBLE);
-            // Compute xtraReg here when we have a float argument
-            assert(xtraReg == REG_NA);
+#ifndef UNIX_AMD64_ABI
+            if (GlobalJitOptions::compFeatureHfa)
+#endif // !UNIX_AMD64_ABI
+            {
+                insCopy = ins_Copy(TYP_DOUBLE);
+                // Compute xtraReg here when we have a float argument
+                assert(xtraReg == REG_NA);
 
-            regMaskTP fpAvailMask;
+                regMaskTP fpAvailMask;
 
-            fpAvailMask = RBM_FLT_CALLEE_TRASH & ~regArgMaskLive;
-#if defined(FEATURE_HFA)
-            fpAvailMask &= RBM_ALLDOUBLE;
-#else
-#if !defined(UNIX_AMD64_ABI)
-#error Error. Wrong architecture.
-#endif // !defined(UNIX_AMD64_ABI)
-#endif // defined(FEATURE_HFA)
+                fpAvailMask = RBM_FLT_CALLEE_TRASH & ~regArgMaskLive;
+                if (GlobalJitOptions::compFeatureHfa)
+                {
+                    fpAvailMask &= RBM_ALLDOUBLE;
+                }
 
-            if (fpAvailMask == RBM_NONE)
-            {
-                fpAvailMask = RBM_ALLFLOAT & ~regArgMaskLive;
-#if defined(FEATURE_HFA)
-                fpAvailMask &= RBM_ALLDOUBLE;
-#else
-#if !defined(UNIX_AMD64_ABI)
-#error Error. Wrong architecture.
-#endif // !defined(UNIX_AMD64_ABI)
-#endif // defined(FEATURE_HFA)
-            }
+                if (fpAvailMask == RBM_NONE)
+                {
+                    fpAvailMask = RBM_ALLFLOAT & ~regArgMaskLive;
+                    if (GlobalJitOptions::compFeatureHfa)
+                    {
+                        fpAvailMask &= RBM_ALLDOUBLE;
+                    }
+                }
 
-            assert(fpAvailMask != RBM_NONE);
+                assert(fpAvailMask != RBM_NONE);
 
-            // We pick the lowest avail register number
-            regMaskTP tempMask = genFindLowestBit(fpAvailMask);
-            xtraReg            = genRegNumFromMask(tempMask);
-#elif defined(TARGET_X86)
+                // We pick the lowest avail register number
+                regMaskTP tempMask = genFindLowestBit(fpAvailMask);
+                xtraReg            = genRegNumFromMask(tempMask);
+            }
+#if defined(TARGET_X86)
             // This case shouldn't occur on x86 since NYI gets converted to an assert
             NYI("Homing circular FP registers via xtraReg");
 #endif
@@ -9562,20 +9560,26 @@ bool Compiler::IsHfa(CORINFO_CLASS_HANDLE hClass)
 
 bool Compiler::IsHfa(GenTree* tree)
 {
-#ifdef FEATURE_HFA
-    return IsHfa(gtGetStructHandleIfPresent(tree));
-#else
-    return false;
-#endif
+    if (GlobalJitOptions::compFeatureHfa)
+    {
+        return IsHfa(gtGetStructHandleIfPresent(tree));
+    }
+    else
+    {
+        return false;
+    }
 }
 
 var_types Compiler::GetHfaType(GenTree* tree)
 {
-#ifdef FEATURE_HFA
-    return GetHfaType(gtGetStructHandleIfPresent(tree));
-#else
-    return TYP_UNDEF;
-#endif
+    if (GlobalJitOptions::compFeatureHfa)
+    {
+        return GetHfaType(gtGetStructHandleIfPresent(tree));
+    }
+    else
+    {
+        return TYP_UNDEF;
+    }
 }
 
 unsigned Compiler::GetHfaCount(GenTree* tree)
@@ -9585,18 +9589,19 @@ unsigned Compiler::GetHfaCount(GenTree* tree)
 
 var_types Compiler::GetHfaType(CORINFO_CLASS_HANDLE hClass)
 {
-#ifdef FEATURE_HFA
-    if (hClass != NO_CLASS_HANDLE)
+    if (GlobalJitOptions::compFeatureHfa)
     {
-        CorInfoHFAElemType elemKind = info.compCompHnd->getHFAType(hClass);
-        if (elemKind != CORINFO_HFA_ELEM_NONE)
+        if (hClass != NO_CLASS_HANDLE)
         {
-            // This type may not appear elsewhere, but it will occupy a floating point register.
-            compFloatingPointUsed = true;
+            CorInfoHFAElemType elemKind = info.compCompHnd->getHFAType(hClass);
+            if (elemKind != CORINFO_HFA_ELEM_NONE)
+            {
+                // This type may not appear elsewhere, but it will occupy a floating point register.
+                compFloatingPointUsed = true;
+            }
+            return HfaTypeFromElemKind(elemKind);
         }
-        return HfaTypeFromElemKind(elemKind);
     }
-#endif // FEATURE_HFA
     return TYP_UNDEF;
 }
 

src/coreclr/jit/compiler.cpp

@@ -54,6 +54,12 @@ bool       Compiler::s_pJitFunctionFileInitialized = false;
 MethodSet* Compiler::s_pJitMethodSet               = nullptr;
 #endif // DEBUG
 
+#ifdef CONFIGURABLE_ARM_ABI
+// static
+bool GlobalJitOptions::compFeatureHfa          = false;
+LONG GlobalJitOptions::compUseSoftFPConfigured = 0;
+#endif // CONFIGURABLE_ARM_ABI
+
 /*****************************************************************************
  *
  *  Little helpers to grab the current cycle counter value; this is done
@@ -468,49 +474,6 @@ var_types Compiler::getJitGCType(BYTE gcType)
     return result;
 }
 
-#ifdef ARM_SOFTFP
-//---------------------------------------------------------------------------
-// IsSingleFloat32Struct:
-//    Check if the given struct type contains only one float32 value type
-//
-// Arguments:
-//    clsHnd     - the handle for the struct type
-//
-// Return Value:
-//    true if the given struct type contains only one float32 value type,
-//    false otherwise.
-//
-
-bool Compiler::isSingleFloat32Struct(CORINFO_CLASS_HANDLE clsHnd)
-{
-    for (;;)
-    {
-        // all of class chain must be of value type and must have only one field
-        if (!info.compCompHnd->isValueClass(clsHnd) || info.compCompHnd->getClassNumInstanceFields(clsHnd) != 1)
-        {
-            return false;
-        }
-
-        CORINFO_CLASS_HANDLE* pClsHnd   = &clsHnd;
-        CORINFO_FIELD_HANDLE  fldHnd    = info.compCompHnd->getFieldInClass(clsHnd, 0);
-        CorInfoType           fieldType = info.compCompHnd->getFieldType(fldHnd, pClsHnd);
-
-        switch (fieldType)
-        {
-            case CORINFO_TYPE_VALUECLASS:
-                clsHnd = *pClsHnd;
-                break;
-
-            case CORINFO_TYPE_FLOAT:
-                return true;
-
-            default:
-                return false;
-        }
-    }
-}
-#endif // ARM_SOFTFP
-
 #ifdef TARGET_X86
 //---------------------------------------------------------------------------
 // isTrivialPointerSizedStruct:
@@ -623,53 +586,44 @@ var_types Compiler::getPrimitiveTypeForStruct(unsigned structSize, CORINFO_CLASS
 
     var_types useType = TYP_UNKNOWN;
 
-// Start by determining if we have an HFA/HVA with a single element.
-#ifdef FEATURE_HFA
+    // Start by determining if we have an HFA/HVA with a single element.
+    if (GlobalJitOptions::compFeatureHfa)
+    {
 #if defined(TARGET_WINDOWS) && defined(TARGET_ARM64)
-    // Arm64 Windows VarArg methods arguments will not classify HFA types, they will need to be treated
-    // as if they are not HFA types.
-    if (!isVarArg)
+        // Arm64 Windows VarArg methods arguments will not classify HFA types, they will need to be treated
+        // as if they are not HFA types.
+        if (!isVarArg)
 #endif // defined(TARGET_WINDOWS) && defined(TARGET_ARM64)
-    {
-        switch (structSize)
         {
-            case 4:
-            case 8:
+            switch (structSize)
+            {
+                case 4:
+                case 8:
 #ifdef TARGET_ARM64
-            case 16:
+                case 16:
 #endif // TARGET_ARM64
-            {
-                var_types hfaType;
-#ifdef ARM_SOFTFP
-                // For ARM_SOFTFP, HFA is unsupported so we need to check in another way.
-                // This matters only for size-4 struct because bigger structs would be processed with RetBuf.
-                if (isSingleFloat32Struct(clsHnd))
-                {
-                    hfaType = TYP_FLOAT;
-                }
-#else  // !ARM_SOFTFP
-                hfaType = GetHfaType(clsHnd);
-#endif // ARM_SOFTFP
-                // We're only interested in the case where the struct size is equal to the size of the hfaType.
-                if (varTypeIsValidHfaType(hfaType))
                 {
-                    if (genTypeSize(hfaType) == structSize)
+                    var_types hfaType = GetHfaType(clsHnd);
+                    // We're only interested in the case where the struct size is equal to the size of the hfaType.
+                    if (varTypeIsValidHfaType(hfaType))
                     {
-                        useType = hfaType;
-                    }
-                    else
-                    {
-                        return TYP_UNKNOWN;
+                        if (genTypeSize(hfaType) == structSize)
+                        {
+                            useType = hfaType;
+                        }
+                        else
+                        {
+                            return TYP_UNKNOWN;
+                        }
                     }
                 }
             }
-        }
-        if (useType != TYP_UNKNOWN)
-        {
-            return useType;
+            if (useType != TYP_UNKNOWN)
+            {
+                return useType;
+            }
         }
     }
-#endif // FEATURE_HFA
 
     // Now deal with non-HFA/HVA structs.
     switch (structSize)
@@ -3273,6 +3227,27 @@ void Compiler::compInitOptions(JitFlags* jitFlags)
     }
 #endif // FEATURE_FASTTAILCALL
 
+#ifdef CONFIGURABLE_ARM_ABI
+    opts.compUseSoftFP        = jitFlags->IsSet(JitFlags::JIT_FLAG_SOFTFP_ABI);
+    unsigned int softFPConfig = opts.compUseSoftFP ? 2 : 1;
+    unsigned int oldSoftFPConfig =
+        InterlockedCompareExchange(&GlobalJitOptions::compUseSoftFPConfigured, softFPConfig, 0);
+    if (oldSoftFPConfig != softFPConfig && oldSoftFPConfig != 0)
+    {
+        // There are no current scenarios where the abi can change during the lifetime of a process
+        // that uses the JIT. If such a change occurs, either compFeatureHfa will need to change to a TLS static
+        // or we will need to have some means to reset the flag safely.
+        NO_WAY("SoftFP ABI setting changed during lifetime of process");
+    }
+
+    GlobalJitOptions::compFeatureHfa = !opts.compUseSoftFP;
+#elif defined(ARM_SOFTFP)
+    // Armel is unconditionally enabled in the JIT. Verify that the VM side agrees.
+    assert(jitFlags->IsSet(JitFlags::JIT_FLAG_SOFTFP_ABI));
+#elif TARGET_ARM
+    assert(!jitFlags->IsSet(JitFlags::JIT_FLAG_SOFTFP_ABI));
+#endif // CONFIGURABLE_ARM_ABI
+
     opts.compScopeInfo = opts.compDbgInfo;
 
 #ifdef LATE_DISASM