From 06c2756e824cfe409d280fc78a0c4f68a9123e49 Mon Sep 17 00:00:00 2001 From: Takayuki 'January June' Suwa Date: Fri, 9 Sep 2022 06:16:31 +0900 Subject: [PATCH] xtensa: Eliminate unused stack frame allocation/freeing 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 boolean member as a flag that controls whether to emit 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 emit insns if not inhibited. (xtensa_expand_epilogue): Change to use the function mentioned above when using the CALL0 ABI. (xtensa_expand_prologue): Ditto. And also change to set the inhibit flag used by xtensa_emit_adjust_stack_ptr() to true if the stack pointer is only used for its own adjustment. --- gcc/config/xtensa/xtensa.cc | 164 ++++++++++++++++++------------------ 1 file changed, 80 insertions(+), 84 deletions(-) diff --git a/gcc/config/xtensa/xtensa.cc b/gcc/config/xtensa/xtensa.cc index 93ac6562b22..0f586b09dfb 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; + bool inhibit_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; } @@ -3139,6 +3140,49 @@ xtensa_initial_elimination_offset (int from, int to ATTRIBUTE_UNUSED) return offset; } +#define ADJUST_SP_NONE 0x0 +#define ADJUST_SP_NEED_NOTE 0x1 +#define ADJUST_SP_FRAME_PTR 0x2 +static void +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 (cfun->machine->inhibit_logues_a1_adjusts) + return; + + 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); + + if (offset < 0) + { + emit_move_insn (tmp_reg, GEN_INT (-offset)); + insn = emit_insn (gen_subsi3 (stack_pointer_rtx, ptr, tmp_reg)); + } + else + { + emit_move_insn (tmp_reg, GEN_INT (offset)); + insn = emit_insn (gen_addsi3 (stack_pointer_rtx, ptr, tmp_reg)); + } + } + + 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); + } +} + /* minimum frame = reg save area (4 words) plus static chain (1 word) and the total number of words must be a multiple of 128 bits. */ #define MIN_FRAME_SIZE (8 * UNITS_PER_WORD) @@ -3174,17 +3218,30 @@ xtensa_expand_prologue (void) int regno; HOST_WIDE_INT offset = 0; int callee_save_size = cfun->machine->callee_save_size; + df_ref ref; + bool stack_pointer_needed = frame_pointer_needed + || crtl->calls_eh_return; + + /* Check if the function body really needs the stack pointer. */ + if (!stack_pointer_needed) + for (ref = DF_REG_USE_CHAIN (A1_REG); + ref; ref = DF_REF_NEXT_REG (ref)) + if (DF_REF_CLASS (ref) == DF_REF_REGULAR + && NONJUMP_INSN_P (DF_REF_INSN (ref))) + stack_pointer_needed = true; + /* Check if callee-saved registers really need saving to the stack. */ + if (!stack_pointer_needed) + for (regno = 0; regno < FIRST_PSEUDO_REGISTER; ++regno) + if (xtensa_call_save_reg (regno)) + stack_pointer_needed = true; + + cfun->machine->inhibit_logues_a1_adjusts = !stack_pointer_needed; /* -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); + xtensa_emit_adjust_stack_ptr (-total_size, + ADJUST_SP_NEED_NOTE); offset = total_size - UNITS_PER_WORD; } else if (callee_save_size) @@ -3194,33 +3251,14 @@ 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); + 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); + xtensa_emit_adjust_stack_ptr (-total_size, + ADJUST_SP_NEED_NOTE); offset = total_size - UNITS_PER_WORD; } } @@ -3242,27 +3280,8 @@ xtensa_expand_prologue (void) } 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); - } + xtensa_emit_adjust_stack_ptr (callee_save_size - total_size, + ADJUST_SP_NEED_NOTE); } if (frame_pointer_needed) @@ -3329,21 +3348,11 @@ xtensa_expand_epilogue (bool sibcall_p) 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 @@ -3384,24 +3393,11 @@ 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)