The following testcase ICEs on aarch64 apparently since the introduction of
the aarch64 port. The reason is that the {ashl,ashr,lshr}<mode>3 expanders
completely unnecessarily FAIL; if operands[2] is something other than
a CONST_INT or REG or MEM and the middle-end code can't cope with the
pattern giving up in these cases. All the expanders use general_operand
predicate for the shift amount operand, but then have just a special case
for CONST_INT (if in-bound, emit an immediate shift, otherwise force into
REG), or MEM (force into REG), or REG (that is the case it handles).
In the testcase, operands[2] is a lowpart SUBREG of a REG, which is valid
general_operand.
I don't see any reason what is magic about MEMs that it should be forced
into REG and others like SUBREGs that it shouldn't, there isn't even a
reason to check for !REG_P because force_reg will do nothing if the operand
is already a REG, and otherwise can handle general_operand just fine.
2020-04-07 Jakub Jelinek <jakub@redhat.com>
PR target/94488
* config/aarch64/aarch64-simd.md (ashl<mode>3, lshr<mode>3,
ashr<mode>3): Force operands[2] into reg whenever it is not CONST_INT.
Assume it is a REG after that instead of testing it and doing FAIL
otherwise. Formatting fix.
* gcc.c-torture/compile/pr94488.c: New test.
