[vm, compiler] Enable argument registers for RISC-V.

dart2js.aot.rv64gc  28061800 -> 27559904 (-1.8%)
dart2js.aot.rv64gcb 27996112 -> 27510728 (-1.7%)

TEST=ci
Bug: #54955
Change-Id: Ic18ab8c33f59c36561fa7e7aed4d06f4e8f8c9dc
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/357215
Reviewed-by: Slava Egorov <[email protected]>
Commit-Queue: Ryan Macnak <[email protected]>

Author: rmacnak-google

runtime/vm/compiler/backend/il.cc

@@ -5978,9 +5978,15 @@ void CachableIdempotentCallInstr::EmitNativeCode(FlowGraphCompiler* compiler) {
       "CachableIdempotentCall pool load and check. pool_index = "
       "%" Pd,
       cacheable_pool_index);
+#if defined(TARGET_ARCH_RISCV32) || defined(TARGET_ARCH_RISCV64)
+  __ MoveRegister(TMP, dst);
+#endif
   __ LoadWordFromPoolIndex(dst, cacheable_pool_index);
   __ CompareImmediate(dst, 0);
   __ BranchIf(NOT_EQUAL, need_to_drop_args ? &drop_args : &done);
+#if defined(TARGET_ARCH_RISCV32) || defined(TARGET_ARCH_RISCV64)
+  __ MoveRegister(dst, TMP);
+#endif
   __ Comment("CachableIdempotentCall pool load and check - end");
 
   ArgumentsInfo args_info(type_args_len(), ArgumentCount(), ArgumentsSize(),

runtime/vm/constants_riscv.h

@@ -67,7 +67,7 @@ enum Register {
   S7 = 23,   // CALLEE_SAVED_TEMP2
   S8 = 24,   // CALLEE_SAVED_TEMP / FAR_TMP
   S9 = 25,   // DISPATCH_TABLE_REG
-  S10 = 26,  // nullptr
+  S10 = 26,  // NULL_REG
   S11 = 27,  // WRITE_BARRIER_STATE
   T3 = 28,
   T4 = 29,
@@ -591,8 +591,10 @@ class CallingConventions {
 //
 // See |compiler::ComputeCallingConvention| for more details.
 struct DartCallingConvention {
-  static constexpr Register kCpuRegistersForArgs[] = {kNoRegister};
-  static constexpr FpuRegister kFpuRegistersForArgs[] = {kNoFpuRegister};
+  // A2-A5 have conflicting uses. The order should be revisited once we
+  // implement Location::MayBeSameAsInput, likely putting A0 first.
+  static constexpr Register kCpuRegistersForArgs[] = {A1, A6, A0, A7};
+  static constexpr FpuRegister kFpuRegistersForArgs[] = {FA0, FA1, FA2, FA3};
 };
 
 // TODO(riscv): Architecture-independent parts of the compiler should use

runtime/vm/object.cc

@@ -27728,7 +27728,8 @@ ErrorPtr EntryPointMemberInvocationError(const Object& member) {
 // dynamic call site.
 intptr_t Function::MaxNumberOfParametersInRegisters(Zone* zone) const {
 #if defined(TARGET_ARCH_X64) || defined(TARGET_ARCH_ARM64) ||                  \
-    defined(TARGET_ARCH_ARM)
+    defined(TARGET_ARCH_ARM) || defined(TARGET_ARCH_RISCV32) ||                \
+    defined(TARGET_ARCH_RISCV64)
   if (!FLAG_precompiled_mode) {
     return 0;
   }