On 02/15/2017 05:06 PM, Aldy Hernandez wrote: > On 02/15/2017 09:49 AM, Martin Liška wrote: >> Hi. >> >> As mentioned in the PR, gimple nops are wrongly handled in >> is_maybe_undefined function. >> Patch can bootstrap on ppc64le-redhat-linux and survives regression tests. > >> >> gimple *def = SSA_NAME_DEF_STMT (t); >> >> + if (!def || gimple_nop_p (def)) >> + return true; >> + > > > Out of curiosity, what is T?
It's a SSA name which belongs to a result_decl: (gdb) p debug_tree(t) <ssa_name 0x7fffdaf3b1f8 type <reference_type 0x7ffff122c9d8 type <record_type 0x7ffff0664888 UnicodeString addressable needs-constructing BLK size <integer_cst 0x7ffff6892030 constant 512> unit size <integer_cst 0x7ffff6931c00 constant 64> align 64 symtab 0 alias set -1 canonical type 0x7ffff66b0e70 fields <field_decl 0x7ffff0669390 D.165781> context <namespace_decl 0x7ffff66954c0 icu_58> pointer_to_this <pointer_type 0x7ffff06791f8> reference_to_this <reference_type 0x7fffea593e70> chain <type_decl 0x7ffff0669428 UnicodeString>> public unsigned DI size <integer_cst 0x7ffff6876be8 constant 64> unit size <integer_cst 0x7ffff6876c00 constant 8> align 64 symtab 0 alias set -1 structural equality> var <result_decl 0x7fffdaf1f528 resultPattern> def_stmt GIMPLE_NOP version 1 ptr-info 0x7fffcc191000> > > Because we early bail out if ssa_undefined_value_p() right before calling > SSA_NAME_DEF_STMT, and ssa_undefined_value_p() will already bail if > gimple_nop_p. > > So T must be one of: > > > /* Parameters get their initial value from the function entry. */ > else if (TREE_CODE (var) == PARM_DECL) > return false; > /* When returning by reference the return address is actually a hidden > parameter. */ > else if (TREE_CODE (var) == RESULT_DECL && DECL_BY_REFERENCE (var)) > return false; This return statement is taken. > /* Hard register variables get their initial value from the ether. */ > else if (VAR_P (var) && DECL_HARD_REGISTER (var)) > return false; > > which I wonder if we should special case in is_maybe_undefined. Do we need a special case in the function? M. > > Aldy