>> In the following RTL, the hardware (reg:HI r2), whose natural mode is >> HImode, is set to 0, but when analysing the REG_EQUAL notes of the MULT >> insn during CSE pass, the (reg:SI r2) is computed to be equivalent to 0, >> which is wrong (the target is big endian). >> >> (insn 51 9 52 3 (set (reg:HI 2 r2) >> (const_int 0 [0])) gcc.c-torture/execute/pr27364.c:5 18 {*movhi1} >> (expr_list:REG_DEAD (reg:HI 31) >> (expr_list:REG_EQUAL (const_int 0 [0]) >> (nil)))) >> >> (insn 52 51 12 3 (set (reg:HI 3 r3 [orig:2+2 ] [2]) >> (reg/v:HI 20 [ number_of_digits_to_use ])) >> gcc.c-torture/execute/pr27364.c:5 18 {*movhi1} >> (expr_list:REG_DEAD (reg/v:HI 20 [ number_of_digits_to_use ]) >> (nil))) >> >> (insn 12 52 13 3 (set (reg:SI 0 r0) >> (const_int 3321928 [0x32b048])) >> gcc.c-torture/execute/pr27364.c:5 19 {movsi} >> (nil)) >> >> (insn 13 12 16 3 (parallel [ >> (set (reg:SI 0 r0) >> (mult:SI (reg:SI 2 r2) >> (reg:SI 0 r0))) >> (clobber (reg:SI 2 r2)) >> ]) gcc.c-torture/execute/pr27364.c:5 54 {*mulsi3_call} >> (expr_list:REG_EQUAL (mult:SI (reg:SI 2 r2) >> (const_int 3321928 [0x32b048])) >> (expr_list:REG_DEAD (reg:HI 3 r3) >> (expr_list:REG_UNUSED (reg:SI 2 r2) >> (nil))))) >> >> >> I think a mode size check is missing when processing REG code in >> cse_process_notes_1. Adding such a check prevents the CSE pass from >> elimintating the MULT instruction. > > It looks like such a check is indeed missing in cse_process_notes_1 (and > probably equiv_constant as well). There is one in insert_regs with a comment > explaining the issue with hard registers. >
OK. I will file a bug and propose a patch ASAP. >> But then this MULT insn is simplified during the combine pass: >> >> Trying 12 -> 13: >> ... >> Successfully matched this instruction: >> (set (reg:SI 0 r0) >> (const_int 0 [0])) >> deferring deletion of insn with uid = 12. >> deferring deletion of insn with uid = 52. >> modifying insn i3 13 r0:SI=0 >> deferring rescan insn with uid = 13. >> >> >> So double middle-end bug or do I miss something? > > Probably a similar issue. I guess the code expects to have subregs of > pseudos > here and isn't prepared for (arithmetic) operations on double-word hard regs. > I will try to track this one down too. Thank you for your reply. Aurélien