# HG changeset patch
# User poonam
# Date 1393584317 28800
# Node ID 8cc154e4a3d62e97cf7102f498f0ee77743d1c21
# Parent  67a853a5a05ca6a9e2ded3c66e58b8d2511b7c0e
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 67a853a5a05c -r 8cc154e4a3d6 src/share/vm/opto/output.cpp
--- a/src/share/vm/opto/output.cpp	Thu Mar 06 13:40:24 2014 -0800
+++ b/src/share/vm/opto/output.cpp	Fri Feb 28 02:45:17 2014 -0800
@@ -345,6 +345,11 @@
   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); )
 
@@ -461,6 +466,7 @@
           last_avoid_back_to_back_adr += max_loop_pad;
         }
         blk_size += max_loop_pad;
+        block_worst_case_pad[i + 1] = max_loop_pad;
       }
     }
 
@@ -500,9 +506,16 @@
         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;