[pushed][PATCH v2] LoongArch: Remove redundant sign extension instructions caused by SLT instructions.
chenglulu
chenglulu@loongson.cn
Mon Aug 28 02:37:26 GMT 2023
Pushed to r14-3511.
在 2023/8/25 下午5:31, Lulu Cheng 写道:
> v1 -> v2:
> 1. Modify description information
>
>
> Since the SLT instruction does not distinguish between 64-bit operations and 32-bit
> operations under the 64-bit LoongArch architecture, if the operand of slt is SImode,
> the sign extension of the operand needs to be displayed.
>
> But similar to the test case below, the sign extension is redundant:
>
> extern int src1, src2, src3;
>
> int
> test (void)
> {
> int data1 = src1 + src2;
> int data2 = src1 + src3;
> return data1 > data2 ? data1 : data2;
> }
> Assembly code before optimization:
> ...
> add.w $r4,$r4,$r14
> add.w $r13,$r13,$r14
> slli.w $r12,$r4,0
> slli.w $r14,$r13,0
> slt $r12,$r12,$r14
> masknez $r4,$r4,$r12
> maskeqz $r12,$r13,$r12
> or $r4,$r4,$r12
> slli.w $r4,$r4,0
> ...
>
> After optimization:
> ...
> add.w $r12,$r12,$r14
> add.w $r13,$r13,$r14
> slt $r4,$r12,$r13
> masknez $r12,$r12,$r4
> maskeqz $r4,$r13,$r4
> or $r4,$r12,$r4
> ...
>
> Similar to this test example, the two operands of SLT are obtained by the
> addition operation, and add.w implicitly sign-extends, so the two operands
> of SLT do not require sign-extend.
>
> gcc/ChangeLog:
>
> * config/loongarch/loongarch.cc (loongarch_expand_conditional_move):
> Optimize the function implementation.
>
> gcc/testsuite/ChangeLog:
>
> * gcc.target/loongarch/slt-sign-extend.c: New test.
> ---
> gcc/config/loongarch/loongarch.cc | 53 +++++++++++++++++--
> .../gcc.target/loongarch/slt-sign-extend.c | 14 +++++
> 2 files changed, 63 insertions(+), 4 deletions(-)
> create mode 100644 gcc/testsuite/gcc.target/loongarch/slt-sign-extend.c
>
> diff --git a/gcc/config/loongarch/loongarch.cc b/gcc/config/loongarch/loongarch.cc
> index 86d58784113..1905599b9e8 100644
> --- a/gcc/config/loongarch/loongarch.cc
> +++ b/gcc/config/loongarch/loongarch.cc
> @@ -4384,14 +4384,30 @@ loongarch_expand_conditional_move (rtx *operands)
> enum rtx_code code = GET_CODE (operands[1]);
> rtx op0 = XEXP (operands[1], 0);
> rtx op1 = XEXP (operands[1], 1);
> + rtx op0_extend = op0;
> + rtx op1_extend = op1;
> +
> + /* Record whether operands[2] and operands[3] modes are promoted to word_mode. */
> + bool promote_p = false;
> + machine_mode mode = GET_MODE (operands[0]);
>
> if (FLOAT_MODE_P (GET_MODE (op1)))
> loongarch_emit_float_compare (&code, &op0, &op1);
> else
> {
> + if ((REGNO (op0) == REGNO (operands[2])
> + || (REGNO (op1) == REGNO (operands[3]) && (op1 != const0_rtx)))
> + && (GET_MODE_SIZE (GET_MODE (op0)) < word_mode))
> + {
> + mode = word_mode;
> + promote_p = true;
> + }
> +
> loongarch_extend_comparands (code, &op0, &op1);
>
> op0 = force_reg (word_mode, op0);
> + op0_extend = op0;
> + op1_extend = force_reg (word_mode, op1);
>
> if (code == EQ || code == NE)
> {
> @@ -4418,23 +4434,52 @@ loongarch_expand_conditional_move (rtx *operands)
> && register_operand (operands[2], VOIDmode)
> && register_operand (operands[3], VOIDmode))
> {
> - machine_mode mode = GET_MODE (operands[0]);
> + rtx op2 = operands[2];
> + rtx op3 = operands[3];
> +
> + if (promote_p)
> + {
> + if (REGNO (XEXP (operands[1], 0)) == REGNO (operands[2]))
> + op2 = op0_extend;
> + else
> + {
> + loongarch_extend_comparands (code, &op2, &const0_rtx);
> + op2 = force_reg (mode, op2);
> + }
> +
> + if (REGNO (XEXP (operands[1], 1)) == REGNO (operands[3]))
> + op3 = op1_extend;
> + else
> + {
> + loongarch_extend_comparands (code, &op3, &const0_rtx);
> + op3 = force_reg (mode, op3);
> + }
> + }
> +
> rtx temp = gen_reg_rtx (mode);
> rtx temp2 = gen_reg_rtx (mode);
>
> emit_insn (gen_rtx_SET (temp,
> gen_rtx_IF_THEN_ELSE (mode, cond,
> - operands[2], const0_rtx)));
> + op2, const0_rtx)));
>
> /* Flip the test for the second operand. */
> cond = gen_rtx_fmt_ee ((code == EQ) ? NE : EQ, GET_MODE (op0), op0, op1);
>
> emit_insn (gen_rtx_SET (temp2,
> gen_rtx_IF_THEN_ELSE (mode, cond,
> - operands[3], const0_rtx)));
> + op3, const0_rtx)));
>
> /* Merge the two results, at least one is guaranteed to be zero. */
> - emit_insn (gen_rtx_SET (operands[0], gen_rtx_IOR (mode, temp, temp2)));
> + if (promote_p)
> + {
> + rtx temp3 = gen_reg_rtx (mode);
> + emit_insn (gen_rtx_SET (temp3, gen_rtx_IOR (mode, temp, temp2)));
> + temp3 = gen_lowpart (GET_MODE (operands[0]), temp3);
> + loongarch_emit_move (operands[0], temp3);
> + }
> + else
> + emit_insn (gen_rtx_SET (operands[0], gen_rtx_IOR (mode, temp, temp2)));
> }
> else
> emit_insn (gen_rtx_SET (operands[0],
> diff --git a/gcc/testsuite/gcc.target/loongarch/slt-sign-extend.c b/gcc/testsuite/gcc.target/loongarch/slt-sign-extend.c
> new file mode 100644
> index 00000000000..ea6b28b7c45
> --- /dev/null
> +++ b/gcc/testsuite/gcc.target/loongarch/slt-sign-extend.c
> @@ -0,0 +1,14 @@
> +/* { dg-do compile } */
> +/* { dg-options "-mabi=lp64d -O2" } */
> +/* { dg-final { scan-assembler-not "slli.w" } } */
> +
> +extern int src1, src2, src3;
> +
> +int
> +test (void)
> +{
> + int data1 = src1 + src2;
> + int data2 = src1 + src3;
> +
> + return data1 > data2 ? data1 : data2;
> +}
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