[Qemu-devel] [PATCH v2] tcg-optimize: Fold sub r,0,x to neg r,x

[Qemu-devel] [PATCH v2] tcg-optimize: Fold sub r,0,x to neg r,x

[Richard Henderson]

Cc: Blue Swirl <blauwirbel@gmail.com>
Signed-off-by: Richard Henderson <rth@twiddle.net>
---
V2 properly does a reset_temp on the output of the neg.
This was the cause of the sparc32 boot problem.

r~
---
 tcg/optimize.c | 34 +++++++++++++++++++++++++++++++++-
 1 file changed, 33 insertions(+), 1 deletion(-)

diff --git a/tcg/optimize.c b/tcg/optimize.c
index bc6e5c1..1b6644c 100644
--- a/tcg/optimize.c
+++ b/tcg/optimize.c
@@ -576,7 +576,8 @@ static TCGArg *tcg_constant_folding(TCGContext *s, uint16_t *tcg_opc_ptr,
             break;
         }
 
-        /* Simplify expressions for "shift/rot r, 0, a => movi r, 0" */
+        /* Simplify expressions for "shift/rot r, 0, a => movi r, 0",
+           and "sub r, 0, a => neg r, a" case.  */
         switch (op) {
         CASE_OP_32_64(shl):
         CASE_OP_32_64(shr):
@@ -592,6 +593,37 @@ static TCGArg *tcg_constant_folding(TCGContext *s, uint16_t *tcg_opc_ptr,
                 continue;
             }
             break;
+        CASE_OP_32_64(sub):
+            {
+                TCGOpcode neg_op;
+                bool have_neg;
+
+                if (temps[args[2]].state == TCG_TEMP_CONST) {
+                    /* Proceed with possible constant folding. */
+                    break;
+                }
+                if (op == INDEX_op_sub_i32) {
+                    neg_op = INDEX_op_neg_i32;
+                    have_neg = TCG_TARGET_HAS_neg_i32;
+                } else {
+                    neg_op = INDEX_op_neg_i64;
+                    have_neg = TCG_TARGET_HAS_neg_i64;
+                }
+                if (!have_neg) {
+                    break;
+                }
+                if (temps[args[1]].state == TCG_TEMP_CONST
+                    && temps[args[1]].val == 0) {
+                    s->gen_opc_buf[op_index] = neg_op;
+                    reset_temp(args[0]);
+                    gen_args[0] = args[0];
+                    gen_args[1] = args[2];
+                    args += 3;
+                    gen_args += 2;
+                    continue;
+                }
+            }
+            break;
         default:
             break;
         }
-- 
1.8.1.4

Re: [Qemu-devel] [PATCH v2] tcg-optimize: Fold sub r, 0, x to neg r, x

[Blue Swirl]

Thanks, applied.

On Thu, Mar 21, 2013 at 4:13 PM, Richard Henderson <rth@twiddle.net> wrote:
> Cc: Blue Swirl <blauwirbel@gmail.com>
> Signed-off-by: Richard Henderson <rth@twiddle.net>
> ---
> V2 properly does a reset_temp on the output of the neg.
> This was the cause of the sparc32 boot problem.
>
> r~
> ---
>  tcg/optimize.c | 34 +++++++++++++++++++++++++++++++++-
>  1 file changed, 33 insertions(+), 1 deletion(-)
>
> diff --git a/tcg/optimize.c b/tcg/optimize.c
> index bc6e5c1..1b6644c 100644
> --- a/tcg/optimize.c
> +++ b/tcg/optimize.c
> @@ -576,7 +576,8 @@ static TCGArg *tcg_constant_folding(TCGContext *s, uint16_t *tcg_opc_ptr,
>              break;
>          }
>
> -        /* Simplify expressions for "shift/rot r, 0, a => movi r, 0" */
> +        /* Simplify expressions for "shift/rot r, 0, a => movi r, 0",
> +           and "sub r, 0, a => neg r, a" case.  */
>          switch (op) {
>          CASE_OP_32_64(shl):
>          CASE_OP_32_64(shr):
> @@ -592,6 +593,37 @@ static TCGArg *tcg_constant_folding(TCGContext *s, uint16_t *tcg_opc_ptr,
>                  continue;
>              }
>              break;
> +        CASE_OP_32_64(sub):
> +            {
> +                TCGOpcode neg_op;
> +                bool have_neg;
> +
> +                if (temps[args[2]].state == TCG_TEMP_CONST) {
> +                    /* Proceed with possible constant folding. */
> +                    break;
> +                }
> +                if (op == INDEX_op_sub_i32) {
> +                    neg_op = INDEX_op_neg_i32;
> +                    have_neg = TCG_TARGET_HAS_neg_i32;
> +                } else {
> +                    neg_op = INDEX_op_neg_i64;
> +                    have_neg = TCG_TARGET_HAS_neg_i64;
> +                }
> +                if (!have_neg) {
> +                    break;
> +                }
> +                if (temps[args[1]].state == TCG_TEMP_CONST
> +                    && temps[args[1]].val == 0) {
> +                    s->gen_opc_buf[op_index] = neg_op;
> +                    reset_temp(args[0]);
> +                    gen_args[0] = args[0];
> +                    gen_args[1] = args[2];
> +                    args += 3;
> +                    gen_args += 2;
> +                    continue;
> +                }
> +            }
> +            break;
>          default:
>              break;
>          }
> --
> 1.8.1.4
>