8278337: riscv: remove unnecessary ld/sd zr around calls

Reviewed-by: fyang

Author: kuaiwei

src/hotspot/cpu/riscv/macroAssembler_riscv.cpp

@@ -953,22 +953,14 @@ void MacroAssembler::pop_reg(Register Rd)
 }
 
 int MacroAssembler::bitset_to_regs(unsigned int bitset, unsigned char* regs) {
-  DEBUG_ONLY(int words_pushed = 0;)
-
   int count = 0;
-  // Sp is x2, and zr is x0, which should not be pushed.
-  // If the number of registers is odd, zr is used for stack alignment.Otherwise, it will be ignored.
-  bitset &= ~ (1U << 2);
-  bitset |= 0x1;
-
   // Scan bitset to accumulate register pairs
   for (int reg = 31; reg >= 0; reg --) {
     if ((1U << 31) & bitset) {
       regs[count++] = reg;
     }
     bitset <<= 1;
   }
-  count &= ~1;  // Only push an even number of regs
   return count;
 }
 
@@ -979,12 +971,14 @@ int MacroAssembler::push_reg(unsigned int bitset, Register stack) {
 
   unsigned char regs[32];
   int count = bitset_to_regs(bitset, regs);
+  // reserve one slot to align for odd count
+  int offset = is_even(count) ? 0 : wordSize;
 
   if (count) {
-    addi(stack, stack, - count * wordSize);
+    addi(stack, stack, - count * wordSize - offset);
   }
   for (int i = count - 1; i >= 0; i--) {
-    sd(as_Register(regs[i]), Address(stack, (count -1 - i) * wordSize));
+    sd(as_Register(regs[i]), Address(stack, (count - 1 - i) * wordSize + offset));
     DEBUG_ONLY(words_pushed ++;)
   }
 
@@ -998,14 +992,16 @@ int MacroAssembler::pop_reg(unsigned int bitset, Register stack) {
 
   unsigned char regs[32];
   int count = bitset_to_regs(bitset, regs);
+  // reserve one slot to align for odd count
+  int offset = is_even(count) ? 0 : wordSize;
 
   for (int i = count - 1; i >= 0; i--) {
-    ld(as_Register(regs[i]), Address(stack, (count -1 - i) * wordSize));
+    ld(as_Register(regs[i]), Address(stack, (count - 1 - i) * wordSize + offset));
     DEBUG_ONLY(words_popped ++;)
   }
 
   if (count) {
-    addi(stack, stack, count * wordSize);
+    addi(stack, stack, count * wordSize + offset);
   }
   assert(words_popped == count, "oops, popped != count");
 

src/hotspot/cpu/riscv/riscv.ad

@@ -1171,19 +1171,18 @@ int MachCallRuntimeNode::ret_addr_offset() {
   //   jal(addr)
   // or with far branches
   //   jal(trampoline_stub)
-  // for real runtime callouts it will be six instructions
+  // for real runtime callouts it will be five instructions
   // see riscv64_enc_java_to_runtime
   //   la(t1, retaddr)
   //   la(t0, RuntimeAddress(addr))
   //   addi(sp, sp, -2 * wordSize)
-  //   sd(zr, Address(sp))
   //   sd(t1, Address(sp, wordSize))
   //   jalr(t0)
   CodeBlob *cb = CodeCache::find_blob(_entry_point);
   if (cb != NULL) {
     return 1 * NativeInstruction::instruction_size;
   } else {
-    return 12 * NativeInstruction::instruction_size;
+    return 11 * NativeInstruction::instruction_size;
   }
 }
 
@@ -2267,7 +2266,6 @@ encode %{
       __ la(t0, RuntimeAddress(entry));
       // Leave a breadcrumb for JavaFrameAnchor::capture_last_Java_pc()
       __ addi(sp, sp, -2 * wordSize);
-      __ sd(zr, Address(sp));
       __ sd(t1, Address(sp, wordSize));
       __ jalr(t0);
       __ bind(retaddr);