https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114714
Robin Dapp <rdapp at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- CC| |rdapp at gcc dot gnu.org --- Comment #5 from Robin Dapp <rdapp at gcc dot gnu.org> --- Did anybody do some further investigation here? Juzhe messaged me that this PR is the original reason for the reversal but I don't yet understand why the register filters don't encompass the full semantics of RVV overlap. I looked into the test case and what happens is that, in order to determine the validity of the alternatives, riscv_get_v_regno_alignment is first being called with an M2 mode. Our destination is actually a (subreg:RVVM2SI (reg:RVVM4SI ...) 0), though. I suppose lra/reload check whether a non-subreg destination also works and hands us a (reg:RVVM4SI ...) as operand[0]. We pass this to riscv_get_v_regno_alignment which, for an LMUL4 mode, returns 4, thus wrongly enabling the W42 alternatives. A W42 alternative permits hard regs % 4 == 2, which causes us to eventually choose vr2 as destination and source. Once the constraints are actually checked we have a mismatch as none of the alternatives work. Now I'm not at all sure how lra/reload use operand[0] here but this can surely be found out. A quick and dirty hack (attached) that checks the insn's destination mode instead of operand[0]'s mode gets rid of the ICE and doesn't cause regressions. I suppose we're too far ahead with the reversal already but I'd really have preferred more details. Maybe somebody has had in-depth look but it just wasn't posted yet? --- a/gcc/config/riscv/riscv.cc +++ b/gcc/config/riscv/riscv.cc @@ -6034,6 +6034,22 @@ riscv_get_v_regno_alignment (machine_mode mode) return lmul; } +int +riscv_get_dest_alignment (rtx_insn *insn, rtx operand) +{ + const_rtx set = 0; + if (GET_CODE (PATTERN (insn)) == SET) + { + set = PATTERN (insn); + rtx op = SET_DEST (set); + return riscv_get_v_regno_alignment (GET_MODE (op)); + } + else + { + return riscv_get_v_regno_alignment (GET_MODE (operand)); + } +} + /* Define ASM_OUTPUT_OPCODE to do anything special before emitting an opcode. */ const char * diff --git a/gcc/config/riscv/riscv.md b/gcc/config/riscv/riscv.md index ce1ee6b9c5e..5113daf2ac7 100644 --- a/gcc/config/riscv/riscv.md +++ b/gcc/config/riscv/riscv.md @@ -550,15 +550,15 @@ (define_attr "group_overlap_valid" "no,yes" (const_string "yes") (and (eq_attr "group_overlap" "W21") - (match_test "riscv_get_v_regno_alignment (GET_MODE (operands[0])) != 2")) + (match_test "riscv_get_dest_alignment (insn, operands[0]) != 2")) (const_string "no") (and (eq_attr "group_overlap" "W42") - (match_test "riscv_get_v_regno_alignment (GET_MODE (operands[0])) != 4")) + (match_test "riscv_get_dest_alignment (insn, operands[0]) != 4")) (const_string "no") (and (eq_attr "group_overlap" "W84") - (match_test "riscv_get_v_regno_alignment (GET_MODE (operands[0])) != 8")) + (match_test "riscv_get_dest_alignment (insn, operands[0]) != 8")) (const_string "no")