simplify-rtx: Fix up SUBREG_PROMOTED_SET arguments [PR104839]

simplify-rtx: Fix up SUBREG_PROMOTED_SET arguments [PR104839]

The following testcase is miscompiled on powerpc64le-linux at -O1 and higher
(except for -Og).  The bug was introduced in r12-3252-gcad36f38576a6a7
which for SIGN_EXTEND from SUBREG_PROMOTED_SIGNED_P SUBREG used
SUBREG_PROMOTED_SET (temp, 1) (but that makes temp
SUBREG_PROMOTED_UNSIGNED_P because SRP_UNSIGNED is 1) and similarly the
ZERO_EXTEND from SUBREG_PROMOTED_UNSIGNED_P SUBREG used
SUBREG_PROMOTED_SET (temp, 0) (but that makes temp
SUBREG_PROMOTED_SIGNED_P because SRP_SIGNED is 0).
The following patch fixes that (swaps the 0s and 1s), but for better
readability uses the SRP_* constants.
rtl.h has:
/* Valid for subregs which are SUBREG_PROMOTED_VAR_P().  In that case
   this gives the necessary extensions:
   0  - signed (SPR_SIGNED)
   1  - normal unsigned (SPR_UNSIGNED)
   2  - value is both sign and unsign extended for mode
        (SPR_SIGNED_AND_UNSIGNED).
   -1 - pointer unsigned, which most often can be handled like unsigned
        extension, except for generating instructions where we need to
        emit special code (ptr_extend insns) on some architectures
        (SPR_POINTER). */
The expr.c change in the same commit looks ok to me (passes unsignedp
to SUBREG_PROMOTED_SET, so 0 for signed, 1 for unsigned).

2022-03-09  Jakub Jelinek  <jakub@redhat.com>

	PR rtl-optimization/104839
	* simplify-rtx.cc (simplify_unary_operation_1) <case SIGN_EXTEND>:
	Use SRP_SIGNED instead of incorrect 1 in SUBREG_PROMOTED_SET.
	(simplify_unary_operation_1) <case ZERO_EXTEND>: Use SRP_UNSIGNED
	instead of incorrect 0 in SUBREG_PROMOTED_SET.

	* gcc.c-torture/execute/pr104839.c: New test.