You can easily get -fcompare-debug failures on AIX with small functions, in 
fact you get the failure for the empty function:

void foo (void) {}

eric@polaris:~/build/gcc/powerpc-ibm-aix7.1> gcc/xgcc -Bgcc -S t.c -O -
fcompare-debug
xgcc: error: t.c: -fcompare-debug failure (length)

Fixed thusly, tested on powerpc-ibm-aix7.1, OK for the mainline?


2015-04-29  Eric Botcazou  <ebotcazou@adacore.com>

	* config/rs6000/rs6000.c (rs6000_stack_info): For XCOFF, replace test
	on debug info with test on optimization to decide stack pushing.


2015-04-29  Eric Botcazou  <ebotcazou@adacore.com>

	* gcc.dg/empty3.c: New test.


-- 
Eric Botcazou