PPC/s390: [wasm] Split jump table and lazy compile table

Port 56eaec9d

Original Commit Message:

    We had both jump slots and lazy compile slots in the same table. This
    increases the space per slot to the maximum of the two, even though we
    often do not use lazy compilation and could have smaller jump slots.
    This CL splits the two into two separate tables. The lazy compile table
    will only be created on demand, and will never be patched.
    The jump table now only contains jumps, and is more compact (which
    might improve performance because of improved locality).

R=clemensh@chromium.org, joransiu@ca.ibm.com, jyan@ca.ibm.com, michael_dawson@ca.ibm.com
BUG=
LOG=N

Change-Id: I7bece77c02f8075da54d664215989339f2958ccd
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1702126Reviewed-by: Clemens Hammacher <clemensh@chromium.org>
Reviewed-by: Junliang Yan <jyan@ca.ibm.com>
Commit-Queue: Milad Farazmand <miladfar@ca.ibm.com>
Cr-Commit-Position: refs/heads/master@{#62740}

src/wasm/jump-table-assembler.cc

@@ -183,12 +183,16 @@ void JumpTableAssembler::NopBytes(int bytes) {
 #elif V8_TARGET_ARCH_PPC64
 void JumpTableAssembler::EmitLazyCompileJumpSlot(uint32_t func_index,
                                                  Address lazy_compile_target) {
+  int start = pc_offset();
   // Load function index to register. max 5 instrs
   mov(kWasmCompileLazyFuncIndexRegister, Operand(func_index));
   // Jump to {lazy_compile_target}. max 5 instrs
   mov(r0, Operand(lazy_compile_target));
   mtctr(r0);
   bctr();
+  int nop_bytes = start + kLazyCompileTableSlotSize - pc_offset();
+  DCHECK_EQ(nop_bytes % kInstrSize, 0);
+  for (int i = 0; i < nop_bytes; i += kInstrSize) nop();
 }
 
 void JumpTableAssembler::EmitRuntimeStubSlot(Address builtin_target) {