ZJIT: Remove PadPatchPoint instructions when lowering to LIR

Basic blocks in LIR should only ever end in control flow instructions
such as jump or return. PadPatchPoint is not control flow, so we should
not emit it at the end of blocks when lowering.

Author: tenderlove

zjit/src/codegen.rs

@@ -333,6 +333,8 @@ fn gen_function(cb: &mut CodeBlock, iseq: IseqPtr, version: IseqVersionRef, func
                     };
 
                     gen_if_false(&mut asm, val_opnd, branch_edge, fall_through_edge);
+                    assert!(asm.current_block().insns.last().unwrap().is_terminator());
+
                     asm.set_current_block(fall_through_target);
 
                     let label = jit.get_label(&mut asm, fall_through_target, block_id);
@@ -356,6 +358,8 @@ fn gen_function(cb: &mut CodeBlock, iseq: IseqPtr, version: IseqVersionRef, func
                     };
 
                     gen_if_true(&mut asm, val_opnd, branch_edge, fall_through_edge);
+                    assert!(asm.current_block().insns.last().unwrap().is_terminator());
+
                     asm.set_current_block(fall_through_target);
 
                     let label = jit.get_label(&mut asm, fall_through_target, block_id);
@@ -368,6 +372,8 @@ fn gen_function(cb: &mut CodeBlock, iseq: IseqPtr, version: IseqVersionRef, func
                         args: target.args.iter().map(|insn_id| jit.get_opnd(*insn_id)).collect()
                     };
                     gen_jump(&mut asm, branch_edge);
+                    assert!(asm.current_block().insns.last().unwrap().is_terminator());
+
                 },
                 _ => {
                     if let Err(last_snapshot) = gen_insn(cb, &mut jit, &mut asm, function, insn_id, &insn) {
@@ -382,8 +388,8 @@ fn gen_function(cb: &mut CodeBlock, iseq: IseqPtr, version: IseqVersionRef, func
                 }
             }
         }
-        // Make sure the last patch point has enough space to insert a jump
-        asm.pad_patch_point();
+        // Blocks should always end with control flow
+        assert!(asm.current_block().insns.last().unwrap().is_terminator());
     }
 
     // Generate code if everything can be compiled