Register-register move instructions that can be easily seen as unnecessary by the human eye may remain in the compiled result. For example:
/* example */ double test(double a, double b) { return __builtin_copysign(a, b); } test: add.n a3, a3, a3 extui a5, a5, 31, 1 ssai 1 ;; Be in the same BB src a7, a5, a3 ;; Replacing the destination doesn't ;; violate any constraints of the ;; operands ;; No CALL insns in this span ;; Both A3 and A7 are irrelevant to ;; insns in this span mov.n a3, a7 ;; An unnecessary reg-reg move ;; A7 is not used after this ret.n The last two instructions above, excluding the return instruction, could be done like this: src a3, a5, a3 This symptom often occurs when handling DI/DFmode values with SImode instructions. This patch solves the above problem using peephole2 pattern. gcc/ChangeLog: * config/xtensa/xtensa.md: New peephole2 pattern that eliminates the occurrence of general-purpose register used only once and for transferring intermediate value. gcc/testsuite/ChangeLog: * gcc.target/xtensa/elim_GP_regmove_[01].c: New. --- gcc/config/xtensa/xtensa.md | 46 +++++++++++++++++++ .../gcc.target/xtensa/elim_GP_regmove_0.c | 23 ++++++++++ .../gcc.target/xtensa/elim_GP_regmove_1.c | 10 ++++ 3 files changed, 79 insertions(+) create mode 100644 gcc/testsuite/gcc.target/xtensa/elim_GP_regmove_0.c create mode 100644 gcc/testsuite/gcc.target/xtensa/elim_GP_regmove_1.c diff --git a/gcc/config/xtensa/xtensa.md b/gcc/config/xtensa/xtensa.md index d3996b26cb5..4c1305c05e7 100644 --- a/gcc/config/xtensa/xtensa.md +++ b/gcc/config/xtensa/xtensa.md @@ -3050,3 +3050,49 @@ FALLTHRU:; operands[1] = GEN_INT (imm0); operands[2] = GEN_INT (imm1); }) + +(define_peephole2 + [(set (match_operand 0 "register_operand") + (match_operand 1 "register_operand"))] + "REG_NREGS (operands[0]) == 1 && GP_REG_P (REGNO (operands[0])) + && REG_NREGS (operands[1]) == 1 && GP_REG_P (REGNO (operands[1])) + && peep2_reg_dead_p (1, operands[1])" + [(const_int 0)] +{ + basic_block bb = BLOCK_FOR_INSN (curr_insn); + rtx_insn *head = BB_HEAD (bb), *insn; + rtx dest = operands[0], src = operands[1], pattern, t_dest, dest_orig; + for (insn = PREV_INSN (curr_insn); + insn && insn != head; + insn = PREV_INSN (insn)) + if (CALL_P (insn)) + break; + else if (INSN_P (insn)) + { + if (GET_CODE (pattern = PATTERN (insn)) == SET + && REG_P (t_dest = SET_DEST (pattern)) + && REG_NREGS (t_dest) == 1 + && REGNO (t_dest) == REGNO (src)) + { + dest_orig = SET_DEST (pattern); + SET_DEST (pattern) = gen_rtx_REG (GET_MODE (t_dest), + REGNO (dest)); + extract_insn (insn); + if (!constrain_operands (true, get_enabled_alternatives (insn))) + { + SET_DEST (pattern) = dest_orig; + goto ABORT; + } + df_insn_rescan (insn); + goto FALLTHRU; + } + if (reg_overlap_mentioned_p (dest, pattern) + || reg_overlap_mentioned_p (src, pattern) + || set_of (dest, insn) + || set_of (src, insn)) + break; + } +ABORT: + FAIL; +FALLTHRU:; +}) diff --git a/gcc/testsuite/gcc.target/xtensa/elim_GP_regmove_0.c b/gcc/testsuite/gcc.target/xtensa/elim_GP_regmove_0.c new file mode 100644 index 00000000000..5c195c357dc --- /dev/null +++ b/gcc/testsuite/gcc.target/xtensa/elim_GP_regmove_0.c @@ -0,0 +1,23 @@ +/* { dg-do compile } */ +/* { dg-options "-O2 -fpeephole2" } */ + +/* can be processed */ +double test0(double a, double b) { + return __builtin_copysign(a, b); +} + +/* cannot be processed: due to violate '0' constraint of the 2nd source operand. */ +int test1(int a, int b) { + int c; + asm volatile ("" : "=a"(c) : "r"(a), "0"(b)); + return c; +} + +/* cannot be processed: due to violate '&' constraint of the destination operand. */ +int test2(int a) { + int b; + asm volatile ("" : "=&a"(b) : "r"(a)); + return b; +} + +/* { dg-final { scan-assembler-times "mov\t|mov.n\t" 2 } } */ diff --git a/gcc/testsuite/gcc.target/xtensa/elim_GP_regmove_1.c b/gcc/testsuite/gcc.target/xtensa/elim_GP_regmove_1.c new file mode 100644 index 00000000000..a13ef818827 --- /dev/null +++ b/gcc/testsuite/gcc.target/xtensa/elim_GP_regmove_1.c @@ -0,0 +1,10 @@ +/* { dg-do compile } */ +/* { dg-options "-O2 -fpeephole2 -mabi=windowed" } */ + +/* cannot be processed: due to violate 'a' constraint of the destination operand of the stack adjustment instruction. */ +void test(void) { + int buffer[8192]; + asm volatile ("" : : "m"(buffer)); +} + +/* { dg-final { scan-assembler-times "movsp" 1 } } */ -- 2.30.2