PR c/46921 Lost side effect when struct initializer expression uses comma operator

PR c/46921 Lost side effect when struct initializer expression uses comma operator

This patch fixes improper handling of comma operator expression in a
struct field initializer as described in:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=46921

Currently, function output_init_element () does not evaluate the left
hand expression in a comma operator that's used for a struct
initializer field if the right hand side is zero-sized. However, the
left hand expression must be evaluated if it's found to have side
effects (for example, a function call).

Patch was successfully bootstrapped and tested on x86_64-linux.

gcc/c:
2018-03-13  David Pagan  <dave.pagan@oracle.com>

	PR c/46921
	* c-typeck.c (output_init_element): Ensure field initializer
	expression is always evaluated if there are side effects.

gcc/testsuite:
2018-03-13  David Pagan  <dave.pagan@oracle.com>

	PR c/46921
	* gcc.dg/pr46921.c: New test.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@258497 138bc75d-0d04-0410-961f-82ee72b054a4