# HG changeset patch
# User aph
# Date 1338303981 14400
# Node ID a14598bd41e5b475954cfdf98cf124141d02059e
# Parent  6a152e87cd76520a14354129fa50b9acb72d91d0
Phase 2

diff -r 6a152e87cd76 -r a14598bd41e5 src/cpu/zero/vm/thumb2.cpp
--- a/src/cpu/zero/vm/thumb2.cpp	Tue May 29 10:11:11 2012 -0400
+++ b/src/cpu/zero/vm/thumb2.cpp	Tue May 29 11:06:21 2012 -0400
@@ -4217,6 +4217,8 @@
   //
   //  n.b. for a return there is no need save or restore locals
 
+  bool is_return = offset == 0;
+
   int r_tmp = Thumb2_Tmp(jinfo, 0);
   unsigned dest;
   if (offset < 0) {
@@ -4255,22 +4257,29 @@
   out_16(jinfo->codebuf, THUMB2_POLLING_PAGE_MAGIC);
 
   {
+    // Flush the stack to memory and save its register state.
     SAVE_STACK(jinfo->jstack);
     Thumb2_Flush(jinfo);
+
     // now the safepoint polling code itself
-    // n.b. no need for save or restore of locals at return i.e. when offset == 0
-    //if (offset != 0) {
+
+    // We save the locals at a return bytecode even though we aren't
+    // going to restore them: we do so because otherwise there's a
+    // risk that the GC might scan garbage.
     Thumb2_save_locals(jinfo, stackdepth);
-    //}
 
     mov_imm(jinfo->codebuf, ARM_R1, bci+CONSTMETHOD_CODEOFFSET);
     add_imm(jinfo->codebuf, ARM_R2, ISTATE_REG(jinfo),
 	    ISTATE_OFFSET(jinfo, stackdepth, 0));
     bl(jinfo->codebuf, handlers[H_SAFEPOINT]);
-    //if (offset != 0) {
-    Thumb2_restore_locals(jinfo, stackdepth);
-    //}
+
+    // We don't restore the locals if we're returning.
+    if (! is_return)
+      Thumb2_restore_locals(jinfo, stackdepth);
+
+    // But we always restore the register state of the stack.
     RESTORE_STACK(jinfo->jstack, jinfo->codebuf);
+
     if (offset < 0) {
       // needs another unconditional backward branch
       branch_uncond(jinfo->codebuf, dest);