On 12/19/24 20:10, Richard Henderson wrote:
> There are only a few logical operations which can compute
> an "affected" mask. Split out handling of this optimization
> to a separate function, only to be called when applicable.
>
> Remove the a_mask field from OptContext, as the mask is
> no longer stored anywhere.
>
> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
> ---
> tcg/optimize.c | 42 +++++++++++++++++++++++++++---------------
> 1 file changed, 27 insertions(+), 15 deletions(-)
>
> diff --git a/tcg/optimize.c b/tcg/optimize.c
> index 453e8c43bd..6757fe0036 100644
> --- a/tcg/optimize.c
> +++ b/tcg/optimize.c
> @@ -64,7 +64,6 @@ typedef struct OptContext {
> QSIMPLEQ_HEAD(, MemCopyInfo) mem_free;
>
> /* In flight values from optimization. */
> - uint64_t a_mask; /* mask bit is 0 iff value identical to first input */
> uint64_t z_mask; /* mask bit is 0 iff value bit is 0 */
> uint64_t s_mask; /* mask of clrsb(value) bits */
> TCGType type;
> @@ -1047,7 +1046,6 @@ static bool fold_const2_commutative(OptContext *ctx, TCGOp *op)
>
> static bool fold_masks(OptContext *ctx, TCGOp *op)
> {
> - uint64_t a_mask = ctx->a_mask;
> uint64_t z_mask = ctx->z_mask;
> uint64_t s_mask = ctx->s_mask;
>
> @@ -1059,7 +1057,6 @@ static bool fold_masks(OptContext *ctx, TCGOp *op)
> * type changing opcodes.
> */
> if (ctx->type == TCG_TYPE_I32) {
> - a_mask = (int32_t)a_mask;
> z_mask = (int32_t)z_mask;
> s_mask |= MAKE_64BIT_MASK(32, 32);
> ctx->z_mask = z_mask;
> @@ -1069,6 +1066,19 @@ static bool fold_masks(OptContext *ctx, TCGOp *op)
> if (z_mask == 0) {
> return tcg_opt_gen_movi(ctx, op, op->args[0], 0);
> }
> + return false;
> +}
> +
> +/*
> + * An "affected" mask bit is 0 if and only if the result is identical
> + * to the first input. Thus if the entire mask is 0, the operation
> + * is equivalent to a copy.
> + */
> +static bool fold_affected_mask(OptContext *ctx, TCGOp *op, uint64_t a_mask)
> +{
> + if (ctx->type == TCG_TYPE_I32) {
> + a_mask = (uint32_t)a_mask;
> + }
> if (a_mask == 0) {
> return tcg_opt_gen_mov(ctx, op, op->args[0], op->args[1]);
> }
> @@ -1305,8 +1315,9 @@ static bool fold_and(OptContext *ctx, TCGOp *op)
> * Known-zeros does not imply known-ones. Therefore unless
> * arg2 is constant, we can't infer affected bits from it.
> */
> - if (arg_is_const(op->args[2])) {
> - ctx->a_mask = z1 & ~z2;
> + if (arg_is_const(op->args[2]) &&
> + fold_affected_mask(ctx, op, z1 & ~z2)) {
> + return true;
> }
>
> return fold_masks(ctx, op);
> @@ -1331,7 +1342,9 @@ static bool fold_andc(OptContext *ctx, TCGOp *op)
> */
> if (arg_is_const(op->args[2])) {
> uint64_t z2 = ~arg_info(op->args[2])->z_mask;
> - ctx->a_mask = z1 & ~z2;
> + if (fold_affected_mask(ctx, op, z1 & ~z2)) {
> + return true;
> + }
> z1 &= z2;
> }
> ctx->z_mask = z1;
> @@ -1709,8 +1722,8 @@ static bool fold_extract(OptContext *ctx, TCGOp *op)
>
> z_mask_old = arg_info(op->args[1])->z_mask;
> z_mask = extract64(z_mask_old, pos, len);
> - if (pos == 0) {
> - ctx->a_mask = z_mask_old ^ z_mask;
> + if (pos == 0 && fold_affected_mask(ctx, op, z_mask_old ^ z_mask)) {
> + return true;
> }
> ctx->z_mask = z_mask;
> ctx->s_mask = smask_from_zmask(z_mask);
> @@ -1777,8 +1790,8 @@ static bool fold_exts(OptContext *ctx, TCGOp *op)
>
> ctx->z_mask = z_mask;
> ctx->s_mask = s_mask;
> - if (!type_change) {
> - ctx->a_mask = s_mask & ~s_mask_old;
> + if (!type_change && fold_affected_mask(ctx, op, s_mask & ~s_mask_old)) {
> + return true;
> }
>
> return fold_masks(ctx, op);
> @@ -1819,8 +1832,8 @@ static bool fold_extu(OptContext *ctx, TCGOp *op)
>
> ctx->z_mask = z_mask;
> ctx->s_mask = smask_from_zmask(z_mask);
> - if (!type_change) {
> - ctx->a_mask = z_mask_old ^ z_mask;
> + if (!type_change && fold_affected_mask(ctx, op, z_mask_old ^ z_mask)) {
> + return true;
> }
> return fold_masks(ctx, op);
> }
> @@ -2482,8 +2495,8 @@ static bool fold_sextract(OptContext *ctx, TCGOp *op)
> s_mask |= MAKE_64BIT_MASK(len, 64 - len);
> ctx->s_mask = s_mask;
>
> - if (pos == 0) {
> - ctx->a_mask = s_mask & ~s_mask_old;
> + if (pos == 0 && fold_affected_mask(ctx, op, s_mask & ~s_mask_old)) {
> + return true;
> }
>
> return fold_masks(ctx, op);
> @@ -2843,7 +2856,6 @@ void tcg_optimize(TCGContext *s)
> }
>
> /* Assume all bits affected, no bits known zero, no sign reps. */
> - ctx.a_mask = -1;
> ctx.z_mask = -1;
> ctx.s_mask = 0;
>
Reviewed-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>