# HG changeset patch
# User iveresov
# Date 1393461915 28800
# Node ID b3e1a903b6e8c624840a51c2762d18a7eb766666
# Parent  78112be27ba0b549700b1c2d90ba8e92efe492b1
8035283: Second phase of branch shortening doesn't account for loop alignment
Summary: added missing check for loop padding case.
Reviewed-by: kvn, jrose

diff -r 78112be27ba0 -r b3e1a903b6e8 src/share/vm/opto/output.cpp
--- a/src/share/vm/opto/output.cpp	Wed Feb 26 11:33:34 2014 -0800
+++ b/src/share/vm/opto/output.cpp	Wed Feb 26 16:45:15 2014 -0800
@@ -344,6 +344,11 @@
   uint*      jmp_offset = NEW_RESOURCE_ARRAY(uint,nblocks);
   uint*      jmp_size   = NEW_RESOURCE_ARRAY(uint,nblocks);
   int*       jmp_nidx   = NEW_RESOURCE_ARRAY(int ,nblocks);
+
+  // Collect worst case block paddings
+  int* block_worst_case_pad = NEW_RESOURCE_ARRAY(int, nblocks);
+  memset(block_worst_case_pad, 0, nblocks * sizeof(int));
+
   DEBUG_ONLY( uint *jmp_target = NEW_RESOURCE_ARRAY(uint,nblocks); )
   DEBUG_ONLY( uint *jmp_rule = NEW_RESOURCE_ARRAY(uint,nblocks); )
 
@@ -460,6 +465,7 @@
           last_avoid_back_to_back_adr += max_loop_pad;
         }
         blk_size += max_loop_pad;
+        block_worst_case_pad[i + 1] = max_loop_pad;
       }
     }
 
@@ -499,9 +505,16 @@
         if (bnum > i) { // adjust following block's offset
           offset -= adjust_block_start;
         }
+
+        // This block can be a loop header, account for the padding
+        // in the previous block.
+        int block_padding = block_worst_case_pad[i];
+        assert(i == 0 || block_padding == 0 || br_offs >= block_padding, "Should have at least a padding on top");
         // In the following code a nop could be inserted before
         // the branch which will increase the backward distance.
-        bool needs_padding = ((uint)br_offs == last_may_be_short_branch_adr);
+        bool needs_padding = ((uint)(br_offs - block_padding) == last_may_be_short_branch_adr);
+        assert(!needs_padding || jmp_offset[i] == 0, "padding only branches at the beginning of block");
+
         if (needs_padding && offset <= 0)
           offset -= nop_size;