YJIT: Optimize putobject+opt_ltlt for integers

In `jit_rb_int_lshift()`, we guard against the right hand side changing
since we want to avoid generating variable length shifts. When control
reaches a `putobject` and `opt_ltlt` pair, though, we know that the right
hand side never changes.

This commit detects this situation and substitutes an implementation
that does not guard against the right hand side changing, saving that
work.

Deleted some `putobject` Rust tests since they aren't that valuable and
cause linking issues.

Nice boost to `optcarrot` and `protoboeuf`:

```
----------  ------------------
bench       yjit-pre/yjit-post
optcarrot   1.09
protoboeuf  1.12
----------  ------------------
```

1 files changed, 81 insertions, 56 deletions

diff --git a/yjit/src/codegen.rs b/yjit/src/codegen.rs
index 0d536907c1..c6e50beab1 100644
--- a/yjit/src/codegen.rs
+++ b/yjit/src/codegen.rs
@@ -30,6 +30,7 @@ pub use crate::virtualmem::CodePtr;
 /// Status returned by code generation functions
 #[derive(PartialEq, Debug)]
 enum CodegenStatus {
+    SkipNextInsn,
     KeepCompiling,
     EndBlock,
 }
@@ -1197,6 +1198,13 @@ pub fn gen_single_block(
         // Move to the next instruction to compile
         insn_idx += insn_len(opcode) as u16;
 
+        // Move past next instruction when instructed
+        if status == Some(SkipNextInsn) {
+            let next_pc = unsafe { rb_iseq_pc_at_idx(iseq, insn_idx.into()) };
+            let next_opcode: usize = unsafe { rb_iseq_opcode_at_pc(iseq, next_pc) }.try_into().unwrap();
+            insn_idx += insn_len(next_opcode) as u16;
+        }
+
         // If the instruction terminates this block
         if status == Some(EndBlock) {
             break;
@@ -1343,7 +1351,7 @@ fn jit_putobject(asm: &mut Assembler, arg: VALUE) {
 fn gen_putobject_int2fix(
     jit: &mut JITState,
     asm: &mut Assembler,
-    _ocb: &mut OutlinedCb,
+    ocb: &mut OutlinedCb,
 ) -> Option<CodegenStatus> {
     let opcode = jit.opcode;
     let cst_val: usize = if opcode == YARVINSN_putobject_INT2FIX_0_.as_usize() {
@@ -1351,22 +1359,86 @@ fn gen_putobject_int2fix(
     } else {
         1
     };
+    let cst_val = VALUE::fixnum_from_usize(cst_val);
+
+    if let Some(result) = fuse_putobject_opt_ltlt(jit, asm, cst_val, ocb) {
+        return Some(result);
+    }
 
-    jit_putobject(asm, VALUE::fixnum_from_usize(cst_val));
+    jit_putobject(asm, cst_val);
     Some(KeepCompiling)
 }
 
 fn gen_putobject(
     jit: &mut JITState,
     asm: &mut Assembler,
-    _ocb: &mut OutlinedCb,
+    ocb: &mut OutlinedCb,
 ) -> Option<CodegenStatus> {
     let arg: VALUE = jit.get_arg(0);
 
+    if let Some(result) = fuse_putobject_opt_ltlt(jit, asm, arg, ocb) {
+        return Some(result);
+    }
+
     jit_putobject(asm, arg);
     Some(KeepCompiling)
 }
 
+/// Combine `putobject` and and `opt_ltlt` together if profitable, for example when
+/// left shifting an integer by a constant amount.
+fn fuse_putobject_opt_ltlt(
+    jit: &mut JITState,
+    asm: &mut Assembler,
+    constant_object: VALUE,
+    ocb: &mut OutlinedCb,
+) -> Option<CodegenStatus> {
+    let next_opcode = unsafe { rb_vm_insn_addr2opcode(jit.pc.add(insn_len(jit.opcode).as_usize()).read().as_ptr()) };
+    if next_opcode == YARVINSN_opt_ltlt as i32 && constant_object.fixnum_p() {
+        // Untag the fixnum shift amount
+        let shift_amt = constant_object.as_isize() >> 1;
+        if shift_amt > 63 || shift_amt < 0 {
+            return None;
+        }
+        if !jit.at_current_insn() {
+            defer_compilation(jit, asm, ocb);
+            return Some(EndBlock);
+        }
+
+        let lhs = jit.peek_at_stack(&asm.ctx, 0);
+        if !lhs.fixnum_p() {
+            return None;
+        }
+
+        if !assume_bop_not_redefined(jit, asm, ocb, INTEGER_REDEFINED_OP_FLAG, BOP_LTLT) {
+            return None;
+        }
+
+        asm_comment!(asm, "integer left shift with rhs={shift_amt}");
+        let lhs = asm.stack_opnd(0);
+
+        // Guard that lhs is a fixnum if necessary
+        let lhs_type = asm.ctx.get_opnd_type(lhs.into());
+        if lhs_type != Type::Fixnum {
+            asm_comment!(asm, "guard arg0 fixnum");
+            asm.test(lhs, Opnd::UImm(RUBY_FIXNUM_FLAG as u64));
+
+            jit_chain_guard(
+                JCC_JZ,
+                jit,
+                asm,
+                ocb,
+                SEND_MAX_DEPTH,
+                Counter::guard_send_not_fixnums,
+            );
+        }
+
+        asm.stack_pop(1);
+        fixnum_left_shift_body(asm, lhs, shift_amt as u64);
+        return Some(SkipNextInsn);
+    }
+    return None;
+}
+
 fn gen_putself(
     _jit: &mut JITState,
     asm: &mut Assembler,
@@ -5073,8 +5145,13 @@ fn jit_rb_int_lshift(
         Counter::lshift_amount_changed,
     );
 
+    fixnum_left_shift_body(asm, lhs, shift_amt as u64);
+    true
+}
+
+fn fixnum_left_shift_body(asm: &mut Assembler, lhs: Opnd, shift_amt: u64) {
     let in_val = asm.sub(lhs, 1.into());
-    let shift_opnd = Opnd::UImm(shift_amt as u64);
+    let shift_opnd = Opnd::UImm(shift_amt);
     let out_val = asm.lshift(in_val, shift_opnd);
     let unshifted = asm.rshift(out_val, shift_opnd);
 
@@ -5087,7 +5164,6 @@ fn jit_rb_int_lshift(
 
     let ret_opnd = asm.stack_push(Type::Fixnum);
     asm.mov(ret_opnd, out_val);
-    true
 }
 
 fn jit_rb_int_rshift(
@@ -10384,57 +10460,6 @@ mod tests {
         assert!(cb.get_write_pos() > 0);
     }
 
-    #[test]
-    fn test_putobject_qtrue() {
-        // Test gen_putobject with Qtrue
-        let (mut jit, _context, mut asm, mut cb, mut ocb) = setup_codegen();
-
-        let mut value_array: [u64; 2] = [0, Qtrue.into()];
-        let pc: *mut VALUE = &mut value_array as *mut u64 as *mut VALUE;
-        jit.pc = pc;
-
-        let status = gen_putobject(&mut jit, &mut asm, &mut ocb);
-
-        let tmp_type_top = asm.ctx.get_opnd_type(StackOpnd(0));
-
-        assert_eq!(status, Some(KeepCompiling));
-        assert_eq!(tmp_type_top, Type::True);
-        asm.compile(&mut cb, None).unwrap();
-        assert!(cb.get_write_pos() > 0);
-    }
-
-    #[test]
-    fn test_putobject_fixnum() {
-        // Test gen_putobject with a Fixnum to test another conditional branch
-        let (mut jit, _context, mut asm, mut cb, mut ocb) = setup_codegen();
-
-        // The Fixnum 7 is encoded as 7 * 2 + 1, or 15
-        let mut value_array: [u64; 2] = [0, 15];
-        let pc: *mut VALUE = &mut value_array as *mut u64 as *mut VALUE;
-        jit.pc = pc;
-
-        let status = gen_putobject(&mut jit, &mut asm, &mut ocb);
-
-        let tmp_type_top = asm.ctx.get_opnd_type(StackOpnd(0));
-
-        assert_eq!(status, Some(KeepCompiling));
-        assert_eq!(tmp_type_top, Type::Fixnum);
-        asm.compile(&mut cb, None).unwrap();
-        assert!(cb.get_write_pos() > 0);
-    }
-
-    #[test]
-    fn test_int2fix() {
-        let (mut jit, _context, mut asm, _cb, mut ocb) = setup_codegen();
-        jit.opcode = YARVINSN_putobject_INT2FIX_0_.as_usize();
-        let status = gen_putobject_int2fix(&mut jit, &mut asm, &mut ocb);
-
-        let tmp_type_top = asm.ctx.get_opnd_type(StackOpnd(0));
-
-        // Right now we're not testing the generated machine code to make sure a literal 1 or 0 was pushed. I've checked locally.
-        assert_eq!(status, Some(KeepCompiling));
-        assert_eq!(tmp_type_top, Type::Fixnum);
-    }
 
     #[test]
     fn test_putself() {