x86: Fix up x86_{,64_}sh{l,r}d patterns [PR103431]

x86: Fix up x86_{,64_}sh{l,r}d patterns [PR103431]

The following testcase is miscompiled because the x86_{,64_}sh{l,r}d
patterns don't properly describe what the instructions do.  One thing
is left out, in particular that there is initial count &= 63 for
sh{l,r}dq and initial count &= 31 for sh{l,r}d{l,w}.  And another thing
not described properly, in particular the behavior when count (after the
masking) is 0.  The pattern says it is e.g.
res = (op0 << op2) | (op1 >> (64 - op2))
but that triggers UB on op1 >> 64.  For op2 0 we actually want
res = (op0 << op2) | 0
When constants are propagated to these patterns during RTL optimizations,
both such problems trigger wrong-code issues.
This patch represents the patterns as e.g.
res = (op0 << (op2 & 63)) | (unsigned long long) ((uint128_t) op1 >> (64 - (op2 & 63)))
so there is both the initial masking and op2 == 0 behavior results in
zero being ored.
The patch introduces alternate patterns for constant op2 where
simplify-rtx.c will fold those expressions into simple numbers,
and define_insn_and_split pre-reload splitter for how the patterns
looked before into the new form, so that it can pattern match during
combine even computations that assumed the shift amount will be in
the range of 1 .. bitsize-1.

2021-11-27  Jakub Jelinek  <jakub@redhat.com>

	PR middle-end/103431
	* config/i386/i386.md (x86_64_shld, x86_shld, x86_64_shrd, x86_shrd):
	Change insn pattern to accurately describe the instructions.
	(*x86_64_shld_1, *x86_shld_1, *x86_64_shrd_1, *x86_shrd_1): New
	define_insn patterns.
	(*x86_64_shld_2, *x86_shld_2, *x86_64_shrd_2, *x86_shrd_2): New
	define_insn_and_split patterns.
	(*ashl<dwi>3_doubleword_mask, *ashl<dwi>3_doubleword_mask_1,
	*<insn><dwi>3_doubleword_mask, *<insn><dwi>3_doubleword_mask_1,
	ix86_rotl<dwi>3_doubleword, ix86_rotr<dwi>3_doubleword): Adjust
	splitters for x86_{,64_}sh{l,r}d pattern changes.

	* gcc.dg/pr103431.c: New test.