This adjusts emit_move_multi_word to handle moves into paradoxical subregs parts that are not there and resolve_clobber to handle such subregs.
Bootstrap & regtest running on x86_64-unknown-linux-gnu. The testcase involves writing to a register out of bounds so I'm not sure this is the correct place to paper over this or whether RTL expansion should have done things differently. ;; MEM[(v4si *)&res] = v_2(D); (insn 12 9 10 (clobber (subreg:TI (reg/v:DI 113 [ res ]) 0)) "pr94574.c":13:18 -1 (nil)) (insn 10 12 11 (set (subreg:SI (reg/v:DI 113 [ res ]) 0) (subreg:SI (reg/v:TI 115 [ v ]) 0)) "pr94574.c":13:18 -1 (nil)) (insn 11 10 0 (set (subreg:SI (reg/v:DI 113 [ res ]) 4) (subreg:SI (reg/v:TI 115 [ v ]) 4)) "pr94574.c":13:18 -1 (nil)) maybe we should simply force regs with out-of-bound accesses to memory? The above is the RTL generated after the first half of the fix. We still generate (insn 12 7 10 2 (clobber (subreg:TI (reg/v:DI 113 [ res ]) 0)) "pr94574.c":13:18 -1 (nil)) which lower-subreg runs into - I did not track down where that is generated, but I understand the subreg is pointless here? Comments? OK? Richard. 2020-04-16 Richard Biener <rguent...@suse.de> PR middle-end/94614 * expr.c (emit_move_multi_word): Do not generate code when the destination part is undefined_operand_subword_p. * lower-subreg.c (resolve_clobber): Look through a paradoxica subreg. --- gcc/expr.c | 5 +++++ gcc/lower-subreg.c | 4 ++++ 2 files changed, 9 insertions(+) diff --git a/gcc/expr.c b/gcc/expr.c index b97c217e86d..dfbeae71518 100644 --- a/gcc/expr.c +++ b/gcc/expr.c @@ -3692,6 +3692,11 @@ emit_move_multi_word (machine_mode mode, rtx x, rtx y) need_clobber = false; for (i = 0; i < CEIL (mode_size, UNITS_PER_WORD); i++) { + /* Do not generate code for a move if it would go entirely + to the non-existing bits of a paradoxical subreg. */ + if (undefined_operand_subword_p (x, i)) + continue; + rtx xpart = operand_subword (x, i, 1, mode); rtx ypart; diff --git a/gcc/lower-subreg.c b/gcc/lower-subreg.c index a170f0ff93b..a11e535b5bf 100644 --- a/gcc/lower-subreg.c +++ b/gcc/lower-subreg.c @@ -1150,6 +1150,10 @@ resolve_clobber (rtx pat, rtx_insn *insn) int ret; reg = XEXP (pat, 0); + /* For clobbers we can look through paradoxical subregs which + we do not handle in simplify_gen_subreg_concatn. */ + if (paradoxical_subreg_p (reg)) + reg = SUBREG_REG (reg); if (!resolve_reg_p (reg) && !resolve_subreg_p (reg)) return false; -- 2.16.4