[PATCH] [MSP430] Fix gcc.dg/pr85180.c and gcc.dg/pr87985.c timeouts for msp430-elf -mlarge

[Jozef Lawrynowicz]

Compilation of gcc.dg/pr85180.c and gcc.dg/pr87985.c times out after 5 minutes
for msp430 with -mlarge.

nonzero_bits1 (from rtlanal.c), recurses many times for each reg
because reg_nonzero_bits_for_combine (combine.c) never considers using 
last_set_nonzero_bits for the given reg when the reg is PSImode (i.e. Pmode for
msp430-elf -mlarge).

nonzero bits for a mode of class MODE_PARTIAL_INT are valid for a mode of class
MODE_INT, and vice-versa. The existing comment in reg_nonzero_bits_for_combine
explaining why last_set_nonzero_bits is valid even when the precision of the
last set mode is less than the current mode, also explains why
MODE_PARTIAL_INT and MODE_INT can be used interchangeably here:

> record_value_for_reg invoked nonzero_bits on the register
> with nonzero_bits_mode (because last_set_mode is necessarily integral
> and HWI_COMPUTABLE_MODE_P in this case) so bits in nonzero_bits_mode
> are all valid, hence in mode too since nonzero_bits_mode is defined
> to the largest HWI_COMPUTABLE_MODE_P mode.

The attached patch fixes the timeout with mlarge (compilation takes only a
couple of seconds) by allowing the last set nonzero bits for a 
reg to be used if either the current mode or last mode is
MODE_PARTIAL_INT or MODE_INT. Currently only MODE_INT is considered.

Successfully bootstrapped and regtested x86_64-pc-linux-gnu and msp430-elf
-msmall and -mlarge.

Ok for trunk?
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