Changes from v1: (xtensa_expand_epilogue): Fixed forgetting to consider hard_frame_pointer_rtx when sharing codes.
--- In the example below, 'x' is once placed on the stack frame and then read into registers as the argument value of bar(): /* example */ struct foo { int a, b; }; extern struct foo bar(struct foo); struct foo test(void) { struct foo x = { 0, 1 }; return bar(x); } Thanks to the dead store elimination, the initialization of 'x' turns into merely loading the immediates to registers, but corresponding stack frame growth is not rolled back. As a result: ;; prereq: the CALL0 ABI ;; before test: addi sp, sp, -16 // unused stack frame allocation/freeing movi.n a2, 0 movi.n a3, 1 addi sp, sp, 16 // because no instructions that refer to j.l bar, a9 // the stack pointer between the two This patch eliminates such unused stack frame allocation/freeing: ;; after test: movi.n a2, 0 movi.n a3, 1 j.l bar, a9 gcc/ChangeLog: * config/xtensa/xtensa.cc (machine_function): New member to track the insns for stack pointer adjustment inside of the pro/epilogue. (xtensa_emit_adjust_stack_ptr): New function to share the common codes and to record the insns for stack pointer adjustment. (xtensa_expand_prologue): Change to use the function mentioned above when using the CALL0 ABI. (xtensa_expand_epilogue): Ditto. And also change to cancel emitting the insns for the stack pointer adjustment if only used for its own. --- gcc/config/xtensa/xtensa.cc | 230 ++++++++++++++++++------------------ 1 file changed, 118 insertions(+), 112 deletions(-) diff --git a/gcc/config/xtensa/xtensa.cc b/gcc/config/xtensa/xtensa.cc index b673b6764da..17416fc6c3f 100644 --- a/gcc/config/xtensa/xtensa.cc +++ b/gcc/config/xtensa/xtensa.cc @@ -102,6 +102,7 @@ struct GTY(()) machine_function int callee_save_size; bool frame_laid_out; bool epilogue_done; + hash_set<rtx_insn *> *logues_a1_adjusts; }; /* Vector, indexed by hard register number, which contains 1 for a @@ -3048,7 +3049,7 @@ xtensa_output_literal (FILE *file, rtx x, machine_mode mode, int labelno) } static bool -xtensa_call_save_reg(int regno) +xtensa_call_save_reg (int regno) { if (TARGET_WINDOWED_ABI) return false; @@ -3084,7 +3085,7 @@ compute_frame_size (poly_int64 size) cfun->machine->callee_save_size = 0; for (regno = 0; regno < FIRST_PSEUDO_REGISTER; ++regno) { - if (xtensa_call_save_reg(regno)) + if (xtensa_call_save_reg (regno)) cfun->machine->callee_save_size += UNITS_PER_WORD; } @@ -3143,6 +3144,51 @@ xtensa_initial_elimination_offset (int from, int to ATTRIBUTE_UNUSED) and the total number of words must be a multiple of 128 bits. */ #define MIN_FRAME_SIZE (8 * UNITS_PER_WORD) +#define ADJUST_SP_NONE 0x0 +#define ADJUST_SP_NEED_NOTE 0x1 +#define ADJUST_SP_FRAME_PTR 0x2 +static rtx_insn * +xtensa_emit_adjust_stack_ptr (HOST_WIDE_INT offset, int flags) +{ + rtx_insn *insn; + rtx ptr = (flags & ADJUST_SP_FRAME_PTR) ? hard_frame_pointer_rtx + : stack_pointer_rtx; + + if (xtensa_simm8 (offset) + || xtensa_simm8x256 (offset)) + insn = emit_insn (gen_addsi3 (stack_pointer_rtx, ptr, GEN_INT (offset))); + else + { + rtx tmp_reg = gen_rtx_REG (Pmode, A9_REG); + rtx_insn* tmp_insn; + + if (offset < 0) + { + tmp_insn = emit_move_insn (tmp_reg, GEN_INT (-offset)); + insn = emit_insn (gen_subsi3 (stack_pointer_rtx, ptr, tmp_reg)); + } + else + { + tmp_insn = emit_move_insn (tmp_reg, GEN_INT (offset)); + insn = emit_insn (gen_addsi3 (stack_pointer_rtx, ptr, tmp_reg)); + } + cfun->machine->logues_a1_adjusts->add (tmp_insn); + } + + if (flags & ADJUST_SP_NEED_NOTE) + { + rtx note_rtx = gen_rtx_SET (stack_pointer_rtx, + plus_constant (Pmode, stack_pointer_rtx, + offset)); + + RTX_FRAME_RELATED_P (insn) = 1; + add_reg_note (insn, REG_FRAME_RELATED_EXPR, note_rtx); + } + + cfun->machine->logues_a1_adjusts->add (insn); + return insn; +} + void xtensa_expand_prologue (void) { @@ -3175,16 +3221,13 @@ xtensa_expand_prologue (void) HOST_WIDE_INT offset = 0; int callee_save_size = cfun->machine->callee_save_size; + cfun->machine->logues_a1_adjusts = new hash_set<rtx_insn *>; + /* -128 is a limit of single addi instruction. */ if (IN_RANGE (total_size, 1, 128)) { - insn = emit_insn (gen_addsi3 (stack_pointer_rtx, stack_pointer_rtx, - GEN_INT (-total_size))); - RTX_FRAME_RELATED_P (insn) = 1; - note_rtx = gen_rtx_SET (stack_pointer_rtx, - plus_constant (Pmode, stack_pointer_rtx, - -total_size)); - add_reg_note (insn, REG_FRAME_RELATED_EXPR, note_rtx); + insn = xtensa_emit_adjust_stack_ptr (-total_size, + ADJUST_SP_NEED_NOTE); offset = total_size - UNITS_PER_WORD; } else if (callee_save_size) @@ -3194,75 +3237,35 @@ xtensa_expand_prologue (void) * move it to its final location. */ if (total_size > 1024) { - insn = emit_insn (gen_addsi3 (stack_pointer_rtx, stack_pointer_rtx, - GEN_INT (-callee_save_size))); - RTX_FRAME_RELATED_P (insn) = 1; - note_rtx = gen_rtx_SET (stack_pointer_rtx, - plus_constant (Pmode, stack_pointer_rtx, - -callee_save_size)); - add_reg_note (insn, REG_FRAME_RELATED_EXPR, note_rtx); + insn = xtensa_emit_adjust_stack_ptr (-callee_save_size, + ADJUST_SP_NEED_NOTE); offset = callee_save_size - UNITS_PER_WORD; } else { - if (xtensa_simm8x256 (-total_size)) - insn = emit_insn (gen_addsi3 (stack_pointer_rtx, - stack_pointer_rtx, - GEN_INT (-total_size))); - else - { - rtx tmp_reg = gen_rtx_REG (Pmode, A9_REG); - emit_move_insn (tmp_reg, GEN_INT (total_size)); - insn = emit_insn (gen_subsi3 (stack_pointer_rtx, - stack_pointer_rtx, tmp_reg)); - } - RTX_FRAME_RELATED_P (insn) = 1; - note_rtx = gen_rtx_SET (stack_pointer_rtx, - plus_constant (Pmode, stack_pointer_rtx, - -total_size)); - add_reg_note (insn, REG_FRAME_RELATED_EXPR, note_rtx); + insn = xtensa_emit_adjust_stack_ptr (-total_size, + ADJUST_SP_NEED_NOTE); offset = total_size - UNITS_PER_WORD; } } for (regno = 0; regno < FIRST_PSEUDO_REGISTER; ++regno) - { - if (xtensa_call_save_reg(regno)) - { - rtx x = gen_rtx_PLUS (Pmode, stack_pointer_rtx, GEN_INT (offset)); - rtx mem = gen_frame_mem (SImode, x); - rtx reg = gen_rtx_REG (SImode, regno); - - offset -= UNITS_PER_WORD; - insn = emit_move_insn (mem, reg); - RTX_FRAME_RELATED_P (insn) = 1; - add_reg_note (insn, REG_FRAME_RELATED_EXPR, - gen_rtx_SET (mem, reg)); - } - } + if (xtensa_call_save_reg (regno)) + { + rtx x = gen_rtx_PLUS (Pmode, stack_pointer_rtx, GEN_INT (offset)); + rtx mem = gen_frame_mem (SImode, x); + rtx reg = gen_rtx_REG (SImode, regno); + + offset -= UNITS_PER_WORD; + insn = emit_move_insn (mem, reg); + RTX_FRAME_RELATED_P (insn) = 1; + add_reg_note (insn, REG_FRAME_RELATED_EXPR, + gen_rtx_SET (mem, reg)); + } if (total_size > 1024 || (!callee_save_size && total_size > 128)) - { - if (xtensa_simm8x256 (callee_save_size - total_size)) - insn = emit_insn (gen_addsi3 (stack_pointer_rtx, - stack_pointer_rtx, - GEN_INT (callee_save_size - - total_size))); - else - { - rtx tmp_reg = gen_rtx_REG (Pmode, A9_REG); - emit_move_insn (tmp_reg, GEN_INT (total_size - - callee_save_size)); - insn = emit_insn (gen_subsi3 (stack_pointer_rtx, - stack_pointer_rtx, tmp_reg)); - } - RTX_FRAME_RELATED_P (insn) = 1; - note_rtx = gen_rtx_SET (stack_pointer_rtx, - plus_constant (Pmode, stack_pointer_rtx, - callee_save_size - - total_size)); - add_reg_note (insn, REG_FRAME_RELATED_EXPR, note_rtx); - } + insn = xtensa_emit_adjust_stack_ptr (callee_save_size - total_size, + ADJUST_SP_NEED_NOTE); } if (frame_pointer_needed) @@ -3326,24 +3329,17 @@ xtensa_expand_epilogue (bool sibcall_p) { int regno; HOST_WIDE_INT offset; + df_ref ref; + bool stack_pointer_used = false; - if (cfun->machine->current_frame_size > (frame_pointer_needed ? 127 : 1024)) + if (cfun->machine->current_frame_size > (frame_pointer_needed ? 127 + : 1024)) { - if (xtensa_simm8x256 (cfun->machine->current_frame_size - - cfun->machine->callee_save_size)) - emit_insn (gen_addsi3 (stack_pointer_rtx, frame_pointer_needed ? - hard_frame_pointer_rtx : stack_pointer_rtx, - GEN_INT (cfun->machine->current_frame_size - - cfun->machine->callee_save_size))); - else - { - rtx tmp_reg = gen_rtx_REG (Pmode, A9_REG); - emit_move_insn (tmp_reg, GEN_INT (cfun->machine->current_frame_size - - cfun->machine->callee_save_size)); - emit_insn (gen_addsi3 (stack_pointer_rtx, frame_pointer_needed ? - hard_frame_pointer_rtx : stack_pointer_rtx, - tmp_reg)); - } + xtensa_emit_adjust_stack_ptr (cfun->machine->current_frame_size - + cfun->machine->callee_save_size, + frame_pointer_needed + ? ADJUST_SP_FRAME_PTR + : ADJUST_SP_NONE); offset = cfun->machine->callee_save_size - UNITS_PER_WORD; } else @@ -3359,19 +3355,18 @@ xtensa_expand_epilogue (bool sibcall_p) emit_insn (gen_blockage ()); for (regno = 0; regno < FIRST_PSEUDO_REGISTER; ++regno) - { - if (xtensa_call_save_reg(regno)) - { - rtx x = gen_rtx_PLUS (Pmode, stack_pointer_rtx, GEN_INT (offset)); - rtx reg; - - offset -= UNITS_PER_WORD; - emit_move_insn (reg = gen_rtx_REG (SImode, regno), - gen_frame_mem (SImode, x)); - if (regno == A0_REG && sibcall_p) - emit_use (reg); - } - } + if (xtensa_call_save_reg (regno)) + { + rtx x = gen_rtx_PLUS (Pmode, stack_pointer_rtx, GEN_INT (offset)); + rtx reg; + + offset -= UNITS_PER_WORD; + emit_move_insn (reg = gen_rtx_REG (SImode, regno), + gen_frame_mem (SImode, x)); + if (regno == A0_REG && sibcall_p) + emit_use (reg); + stack_pointer_used = true; + } if (cfun->machine->current_frame_size > 0) { @@ -3384,31 +3379,42 @@ xtensa_expand_epilogue (bool sibcall_p) else offset = cfun->machine->callee_save_size; if (offset) - emit_insn (gen_addsi3 (stack_pointer_rtx, - stack_pointer_rtx, - GEN_INT (offset))); + xtensa_emit_adjust_stack_ptr (offset, ADJUST_SP_NONE); } else - { - if (xtensa_simm8x256 (cfun->machine->current_frame_size)) - emit_insn (gen_addsi3 (stack_pointer_rtx, stack_pointer_rtx, - GEN_INT (cfun->machine->current_frame_size))); - else - { - rtx tmp_reg = gen_rtx_REG (Pmode, A9_REG); - emit_move_insn (tmp_reg, - GEN_INT (cfun->machine->current_frame_size)); - emit_insn (gen_addsi3 (stack_pointer_rtx, stack_pointer_rtx, - tmp_reg)); - } - } + xtensa_emit_adjust_stack_ptr (cfun->machine->current_frame_size, + ADJUST_SP_NONE); } if (crtl->calls_eh_return) emit_insn (gen_add3_insn (stack_pointer_rtx, stack_pointer_rtx, EH_RETURN_STACKADJ_RTX)); + + /* Check if the function body uses the stack pointer. */ + for (ref = DF_REG_USE_CHAIN (A1_REG); + ref; ref = DF_REF_NEXT_REG (ref)) + if (DF_REF_CLASS (ref) == DF_REF_REGULAR) + { + stack_pointer_used = true; + break; + } + + /* Undo the insns if the stack pointer is only used for its own + adjustment. */ + if (! (stack_pointer_used + || frame_pointer_needed + || crtl->calls_eh_return)) + for (const auto &insn : *cfun->machine->logues_a1_adjusts) + { + rtx note = find_reg_note (insn, REG_FRAME_RELATED_EXPR, NULL); + + if (note) + remove_note (insn, note); + PATTERN (insn) = const0_rtx; + } } + cfun->machine->epilogue_done = true; if (!sibcall_p) emit_jump_insn (gen_return ()); -- 2.20.1