[PATCH][rs6000][PR target/82190] fix mem size info in rtl generated by memcmp and strncmp/strcmp builtin expansion

[Aaron Sawdey]

In the code I put in gcc7 for expanding memcmp and strcmp/strncmp as
builtins, I used set_mem_size to set the size of loads to only the
bytes I was actually going to compare. However this is really incorrect
and the test case for 82190 was failing because alias analysis believed
the bogus size and though there was no conflict between an 8byte load
used for comparing 6 bytes and a later store to the 7th byte. As a
result it eliminated that load from the 7 byte compare that followed
later.

This patch changes the set_mem_size calls in expand_block_move and
expand_strn_compare to set the size to the size of the load being done
regardless of how many bytes are being used.

OK for trunk if bootstrap/regtest passes on ppc64le?

2017-12-12  Aaron Sawdey  <acsawdey@linux.vnet.ibm.com>

	PR target/82190
	* config/rs6000/rs6000-string.c (expand_block_move,
	expand_strn_compare): fix set_mem_size() calls.

-- 
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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