[RS6000] Change maddld match_operand from DI to GPR

[RS6000] Change maddld match_operand from DI to GPR

From PowerPC ISA3.0, the description of `maddld RT, RA.RB, RC` is as follows:
64-bit RA and RB are multiplied and then the RC is signed extend to 128 bits,
and add them together.

We only apply it to 64-bit mode (DI) when implementing maddld.  However, if we
can guarantee that the result of the maddld operation will be limited to 32-bit
mode (SI), we can still apply it to 32-bit mode (SI).

gcc/ChangeLog
2019-06-26  Li Jia He  <helijia@linux.ibm.com>

	* config/rs6000/rs6000.h (TARGET_MADDLD): Remove the restriction of
	TARGET_POWERPC64.
	* config/rs6000/rs6000.md (maddld): Change maddld match_operand from DI
	to GPR.

gcc/testsuite/ChangeLog
2019-06-26  Li Jia He  <helijia@linux.ibm.com>

	* gcc.target/powerpc/maddld-1.c: New testcase.

From-SVN: r272673