Do not simplify "(and (reg) (const bit)" to if_then_else.

Do not simplify "(and (reg) (const bit)" to if_then_else.

combine_simplify_rtx() tries to replace rtx expressions with just two
possible values with an experession that uses if_then_else:

  (if_then_else (condition) (value1) (value2))

If the original expression is e.g.

  (and (reg) (const_int 2))

where the constant is the mask for a single bit, the replacement results
in a more complex expression than before:

  (if_then_else (ne (zero_extract (reg) (1) (31))) (2) (0))

Similar replacements are done for

  (signextend (and ...))
  (zeroextend (and ...))

Suppress the replacement this special case in if_then_else_cond().

gcc/ChangeLog:

2016-12-02  Dominik Vogt  <vogt@linux.vnet.ibm.com>

	* combine.c (combine_simplify_rtx):  Suppress replacement of
	"(and (reg) (const_int bit))" with "if_then_else".

From-SVN: r243162