lower-bitint: Make temporarily wrong IL less wrong [PR112843]

lower-bitint: Make temporarily wrong IL less wrong [PR112843]

As discussed in the PR, for the middle (on x86-64 65..128 bit) _BitInt
types like
  _1 = x_4(D) * 5;
where _1 and x_4(D) have _BitInt(128) type and x is PARM_DECL, the bitint
lowering pass wants to replace this with
  _13 = (int128_t) x_4(D);
  _12 = _13 * 5;
  _1 = (_BitInt(128)) _12;
where _13 and _12 have int128_t type and the ranger ICEs when the IL is
temporarily invalid:
during GIMPLE pass: bitintlower
pr112843.c: In function ‘foo’:
pr112843.c:7:1: internal compiler error: Segmentation fault
    7 | foo (_BitInt (128) x, _BitInt (256) y)
      | ^~~
0x152943f crash_signal
        ../../gcc/toplev.cc:316
0x25c21c8 ranger_cache::range_of_expr(vrange&, tree_node*, gimple*)
        ../../gcc/gimple-range-cache.cc:1204
0x25cdcf9 fold_using_range::range_of_range_op(vrange&, gimple_range_op_handler&, fur_source&)
        ../../gcc/gimple-range-fold.cc:671
0x25cf9a0 fold_using_range::fold_stmt(vrange&, gimple*, fur_source&, tree_node*)
        ../../gcc/gimple-range-fold.cc:602
0x25b5520 gimple_ranger::update_stmt(gimple*)
        ../../gcc/gimple-range.cc:564
0x16f1234 update_stmt_operands(function*, gimple*)
        ../../gcc/tree-ssa-operands.cc:1150
0x117a5b6 update_stmt_if_modified(gimple*)
        ../../gcc/gimple-ssa.h:187
0x117a5b6 update_stmt_if_modified(gimple*)
        ../../gcc/gimple-ssa.h:184
0x117a5b6 update_modified_stmt
        ../../gcc/gimple-iterator.cc:44
0x117a5b6 gsi_insert_after(gimple_stmt_iterator*, gimple*, gsi_iterator_update)
        ../../gcc/gimple-iterator.cc:544
0x25abc2f gimple_lower_bitint
        ../../gcc/gimple-lower-bitint.cc:6348

What the code does right now is, it first creates a new SSA_NAME (_12
above), adds the
  _1 = (_BitInt(128)) _12;
stmt after it (where it crashes, because _12 has no SSA_NAME_DEF_STMT yet),
then sets lhs of the previous stmt to _12 (this is also temporarily
incorrect, there are incompatible types involved in the stmt), later on
changes also operands and finally update_stmt it.

The following patch instead changes the lhs of the stmt before adding the
cast after it.  The question is if this is less or more wrong temporarily
(but the ICE is gone).  In addition to that the patch moves the operand
adjustments before the lhs adjustment.

The reason I tweaked the lhs first is that it then just uses gimple_op and
iterates over all ops, if that is done before lhs it would need to special
case which op to skip because it is lhs (I'm using gimple_get_lhs for the
lhs, but this isn't done for GIMPLE_CALL nor GIMPLE_PHI, so GIMPLE_ASSIGN
or say GIMPLE_GOTO etc. are the only options).

2023-12-05  Jakub Jelinek  <jakub@redhat.com>

	PR tree-optimization/112843
	* gimple-lower-bitint.cc (gimple_lower_bitint): Change lhs of stmt
	to lhs2 before building and inserting lhs = (cast) lhs2; assignment.
	Adjust stmt operands before adjusting lhs.

	* gcc.dg/bitint-47.c: New test.