YJIT: Use u32 for CodePtr to save 4 bytes each

We've long had a size restriction on the code memory region such that a
u32 could refer to everything. This commit capitalizes on this
restriction by shrinking the size of `CodePtr` to be 4 bytes from 8.

To derive a full raw pointer from a `CodePtr`, one needs a base pointer.
Both `CodeBlock` and `VirtualMemory` can be used for this purpose. The
base pointer is readily available everywhere, except for in the case of
the `jit_return` "branch". Generalize lea_label() to lea_jump_target()
in the IR to delay deriving the `jit_return` address until `compile()`,
when the base pointer is available.

On railsbench, this yields roughly a 1% reduction to `yjit_alloc_size`
(58,397,765 to 57,742,248).

1 files changed, 3 insertions, 3 deletions

diff --git a/yjit/src/backend/tests.rs b/yjit/src/backend/tests.rs
index 774a02dc6b..ad46321ace 100644
--- a/yjit/src/backend/tests.rs
+++ b/yjit/src/backend/tests.rs
@@ -231,7 +231,7 @@ fn test_jcc_ptr()
 {
     let (mut asm, mut cb) = setup_asm();
 
-    let side_exit = Target::CodePtr(((cb.get_write_ptr().raw_ptr() as usize + 4) as *mut u8).into());
+    let side_exit = Target::CodePtr(cb.get_write_ptr().add_bytes(4));
     let not_mask = asm.not(Opnd::mem(32, EC, RUBY_OFFSET_EC_INTERRUPT_MASK));
     asm.test(
         Opnd::mem(32, EC, RUBY_OFFSET_EC_INTERRUPT_FLAG),
@@ -248,7 +248,7 @@ fn test_jmp_ptr()
 {
     let (mut asm, mut cb) = setup_asm();
 
-    let stub = Target::CodePtr(((cb.get_write_ptr().raw_ptr() as usize + 4) as *mut u8).into());
+    let stub = Target::CodePtr(cb.get_write_ptr().add_bytes(4));
     asm.jmp(stub);
 
     asm.compile_with_num_regs(&mut cb, 0);
@@ -259,7 +259,7 @@ fn test_jo()
 {
     let (mut asm, mut cb) = setup_asm();
 
-    let side_exit = Target::CodePtr(((cb.get_write_ptr().raw_ptr() as usize + 4) as *mut u8).into());
+    let side_exit = Target::CodePtr(cb.get_write_ptr().add_bytes(4));
 
     let arg1 = Opnd::mem(64, SP, 0);
     let arg0 = Opnd::mem(64, SP, 8);