From 438346fc26b35e5555441398c7b54b36169b0fa9 Mon Sep 17 00:00:00 2001
From: Alex Shinn <alexshinn@gmail.com>
Date: Wed, 3 Jun 2015 22:29:38 +0900
Subject: [PATCH] When aligning bytecode, pad the skipped bytes with the
 previous opcode. This allows for instructions which want to save the previous
 ip to simply subtract their operands without needing to preserve the original
 ip in advance.

---
 vm.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/vm.c b/vm.c
index e0631dfc..7f61bad6 100644
--- a/vm.c
+++ b/vm.c
@@ -84,10 +84,14 @@ sexp sexp_stack_trace_op (sexp ctx, sexp self, sexp_sint_t n, sexp out) {
 
 #if SEXP_USE_ALIGNED_BYTECODE
 void sexp_context_align_pos(sexp ctx) {
-  sexp_uint_t pos = sexp_unbox_fixnum(sexp_context_pos(ctx));
+  sexp_uint_t i, pos = sexp_unbox_fixnum(sexp_context_pos(ctx));
   sexp_uint_t new_pos = sexp_word_align(pos);
   if (new_pos > pos) {
     sexp_expand_bcode(ctx, (sexp_sint_t)new_pos - pos);
+    if (pos > 0)
+      for (i=pos; i<new_pos; ++i)
+        sexp_bytecode_data(sexp_context_bc(ctx))[i] =
+          sexp_bytecode_data(sexp_context_bc(ctx))[pos-1];
     sexp_context_pos(ctx) = sexp_make_fixnum(new_pos);
   }
 }