[PATCH][PR target/79449][7 regression] fix ppc strncmp builtin expansion runtime boundary crossing check

[Aaron Sawdey]

Basic problem is that the runtime check for a 4k boundary crossing was
checking that it didn't happen in the N bytes strncmp was being asked
to look at. But, the code generation after the check assumed it could
generate an 8-byte read and so it could step over the boundary. 

The fix is to make sure that the minimum distance to the boundary being
checked and the maximum read size being generated for these short
comparisons are in sync.

The added test case tests for this condition against both memcmp and
strncmp builtin expansion.

Assuming bootstrap/regtest passes on ppc variants and the new test case
passes on x86_64 as well, ok for trunk?


2017-02-09  Aaron Sawdey  <acsawdey@linux.vnet.ibm.com>

	PR target/79449
	* gcc.dg/strncmp-2.c: New.  Test strncmp and memcmp builtin
	expansion for reading beyond a 4k boundary.

2017-02-09  Aaron Sawdey  <acsawdey@linux.vnet.ibm.com>

	PR target/79449
	* config/rs6000/rs6000.c (expand_block_compare): Make sure runtime
	boundary crossing check and subsequent code generation agree.

-- 
Aaron Sawdey, Ph.D.  acsawdey@linux.vnet.ibm.com
050-2/C113  (507) 253-7520 home: 507/263-0782
IBM Linux Technology Center - PPC Toolchain
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