From 782e442e4f3b88937a725a01245dd749f3f893b9 Mon Sep 17 00:00:00 2001 From: Max Filippov Date: Wed, 22 Feb 2023 22:08:21 -0800 Subject: [PATCH] xtensa: fix PR target/108876 In commit b2ef02e8cbbaf95fee98be255f697f47193960ec, the sibling call insn included (use (reg:SI A0_REG)) to fix the problem, which added a USE chain unconditionally to the data flow of register A0 during the sibling call. As a result, df_regs_ever_live_p (A0_REG) returns true, so even if register A0 is not used outside of the sibling call insn, saves and restores to stack slots are emitted in pro/epilogue, and finally code size increases. (This is why I never included (use A0) in sibling calls) /* example */ extern int foo(int); int test(int a) { return foo(a * 3 + 1); } ;; before test: addi sp, sp, -16 ;; unneeded stack frame allocation (induced) s32i.n a0, sp, 12 ;; unneeded saving of register A0 l32i.n a0, sp, 12 ;; unneeded restoration of register A0 addx2 a2, a2, a2 addi.n a2, a2, 1 addi sp, sp, 16 ;; unneeded stack frame freeing (induced) j.l foo, a9 ;; sibling call (truly needs register A0) The essential cause is that we emit (use A0) *before* the insns that does the stack pointer adjustment during epilogue expansion, so the liveness of register A0 ends early, so register A0 is reused afterwards. This patch fixes the problem and avoids such regression by doing the emit of (use A0) in the sibling call epilogue expansion at the end. ;; after test: addx2 a2, a2, a2 addi.n a2, a2, 1 j.l foo, a9 >From RTL-pass "315r.rnreg" by "gfortran -O3 -funroll-loops -mabi=call0 -S -da gcc-gnu/gcc/testsuite/gfortran.dg/allocate_with_source_5.f90": ;; Function selector_init (__selectors_MOD_selector_init, funcdef_no=2, decl_uid=987, cgraph_uid=3, symbol_order=4) ... (insn 3807 3806 3808 121 (set (reg:SI 15 a15) (mem/c:SI (plus:SI (reg/f:SI 1 sp) (const_int 268 [0x10c])) [31 S4 A32])) "gcc-gnu/gcc/testsuite/gfortran.dg/allocate_with_source_5.f90":35:30 53 {movsi_internal} (nil)) (insn 3808 3807 3809 121 (set (reg:SI 7 a7) (const_int 288 [0x120])) "gcc-gnu/gcc/testsuite/gfortran.dg/allocate_with_source_5.f90":35:30 53 {movsi_internal} (nil)) (insn 3809 3808 3810 121 (set (reg/f:SI 1 sp) (plus:SI (reg/f:SI 1 sp) (reg:SI 7 a7))) "gcc-gnu/gcc/testsuite/gfortran.dg/allocate_with_source_5.f90":35:30 1 {addsi3} (expr_list:REG_DEAD (reg:SI 9 a9) (nil))) (insn 3810 3809 721 121 (use (reg:SI 0 a0)) "gcc-gnu/gcc/testsuite/gfortran.dg/allocate_with_source_5.f90":35:30 -1 (expr_list:REG_DEAD (reg:SI 0 a0) (nil))) (call_insn/j 721 3810 722 121 (call (mem:SI (symbol_ref:SI ("free") [flags 0x41] ) [0 __builtin_free S4 A32]) (const_int 0 [0])) "gcc-gnu/gcc/testsuite/gfortran.dg/allocate_with_source_5.f90":35:30 discrim 1 106 {sibcall_internal} (expr_list:REG_DEAD (reg:SI 2 a2) (expr_list:REG_CALL_DECL (symbol_ref:SI ("free") [flags 0x41] ) (expr_list:REG_EH_REGION (const_int 0 [0]) (nil)))) (expr_list:SI (use (reg:SI 2 a2)) (nil))) (IMHO the "rnreg" pass doesn't take REG_ALLOC_ORDER into account; it just seems to allocate registers in fixed_regs index order, which may have hurt register A0 that became allocatable in the recent patch) gcc/ChangeLog: PR target/108876 * config/xtensa/xtensa.cc (xtensa_expand_epilogue): Emit (use (reg:SI A0_REG)) at the end in the sibling call (i.e. the same place as (return) in the normal call). --- gcc/config/xtensa/xtensa.cc | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/gcc/config/xtensa/xtensa.cc b/gcc/config/xtensa/xtensa.cc index d0320ef..b80eef5 100644 --- a/gcc/config/xtensa/xtensa.cc +++ b/gcc/config/xtensa/xtensa.cc @@ -3548,8 +3548,6 @@ xtensa_expand_epilogue (bool sibcall_p) gen_frame_mem (SImode, x)); } } - if (sibcall_p) - emit_use (gen_rtx_REG (SImode, A0_REG)); if (cfun->machine->current_frame_size > 0) { @@ -3575,7 +3573,9 @@ xtensa_expand_epilogue (bool sibcall_p) EH_RETURN_STACKADJ_RTX)); } cfun->machine->epilogue_done = true; - if (!sibcall_p) + if (sibcall_p) + emit_use (gen_rtx_REG (SImode, A0_REG)); + else emit_jump_insn (gen_return ()); } -- 2.7.4