On Wed, Dec 20, 2017 at 2:56 PM, Wilco Dijkstra <wilco.dijks...@arm.com> wrote:
> This patch fixes PR83491 - if an SSA expression contains 2 identical float
> constants, the division reciprocal optimization will ICE. Fix this by
> explicitly
> checking for SSA_NAME in the tree code before walking the uses. Also fix
> several
> coding style issues pointed out by Jakub and make comments more readable.
>
> Bootstrap OK, OK for trunk?
>
> ChangeLog:
> 2017-12-20 Wilco Dijkstra <wdijk...@arm.com>
>
> gcc/
> PR tree-optimization/83491
> * tree-ssa-math-opts.c (execute_cse_reciprocals_1): Check for SSA_NAME
> before walking uses. Improve coding style and comments.
>
> gcc/testsuite/
> PR tree-optimization/83491
> * gcc.dg/pr83491.c: Add new test.
> --
>
> diff --git a/gcc/testsuite/gcc.dg/pr83491.c b/gcc/testsuite/gcc.dg/pr83491.c
> new file mode 100644
> index
> 0000000000000000000000000000000000000000..f23cc19c72f57ca8d34f05f28fee75fc2c13f33a
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/pr83491.c
> @@ -0,0 +1,10 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O1 -funsafe-math-optimizations" } */
> +
> +float a;
> +float b;
> +void bar ()
> +{
> + a = __builtin_nanf ("");
> + b = __builtin_powf (a, 2.5F);
> +}
> diff --git a/gcc/tree-ssa-math-opts.c b/gcc/tree-ssa-math-opts.c
> index
> 8db12f5e1cd5d227bd6c3780420e93cd3fe7b435..4e8f5e728d0c8ef5ac564d8c3c999d8a6ff15e7e
> 100644
> --- a/gcc/tree-ssa-math-opts.c
> +++ b/gcc/tree-ssa-math-opts.c
> @@ -544,29 +544,32 @@ execute_cse_reciprocals_1 (gimple_stmt_iterator
> *def_gsi, tree def)
> int square_recip_count = 0;
> int sqrt_recip_count = 0;
>
> - gcc_assert (FLOAT_TYPE_P (TREE_TYPE (def)) && is_gimple_reg (def));
> + gcc_assert (FLOAT_TYPE_P (TREE_TYPE (def)) && is_gimple_reg (def)
> + && TREE_CODE (def) == SSA_NAME);
The is_gimple_reg () predicate test is now redundant.
> threshold = targetm.min_divisions_for_recip_mul (TYPE_MODE (TREE_TYPE
> (def)));
>
> - /* If this is a square (x * x), we should check whether there are any
> - enough divisions by x on it's own to warrant waiting for that pass. */
> - if (TREE_CODE (def) == SSA_NAME)
> + /* If DEF is a square (x * x), count the number of divisions by x.
> + If there are more divisions by x than by (DEF * DEF), prefer to optimize
> + the reciprocal of x instead of DEF. This improves cases like:
> + def = x * x
> + t0 = a / def
> + t1 = b / def
> + t2 = c / x
> + Reciprocal optimization of x results in 1 division rather than 2 or 3.
> */
> + gimple *def_stmt = SSA_NAME_DEF_STMT (def);
> +
> + if (is_gimple_assign (def_stmt)
> + && gimple_assign_rhs_code (def_stmt) == MULT_EXPR
> + && TREE_CODE (gimple_assign_rhs1 (def_stmt)) == SSA_NAME
> + && gimple_assign_rhs1 (def_stmt) == gimple_assign_rhs2 (def_stmt))
> {
> - gimple *def_stmt = SSA_NAME_DEF_STMT (def);
> + tree op0 = gimple_assign_rhs1 (def_stmt);
>
> - if (is_gimple_assign (def_stmt)
> - && gimple_assign_rhs_code (def_stmt) == MULT_EXPR
> - && gimple_assign_rhs1 (def_stmt) == gimple_assign_rhs2 (def_stmt))
> + FOR_EACH_IMM_USE_FAST (use_p, use_iter, op0)
> {
> - /* This statement is a square of something. We should take this
> - in to account, as it may be more profitable to not extract
> - the reciprocal here. */
> - tree op0 = gimple_assign_rhs1 (def_stmt);
> - FOR_EACH_IMM_USE_FAST (use_p, use_iter, op0)
> - {
> - gimple *use_stmt = USE_STMT (use_p);
> - if (is_division_by (use_stmt, op0))
> - sqrt_recip_count ++;
> - }
> + gimple *use_stmt = USE_STMT (use_p);
> + if (is_division_by (use_stmt, op0))
> + sqrt_recip_count++;
> }
> }
>
> @@ -587,26 +590,23 @@ execute_cse_reciprocals_1 (gimple_stmt_iterator
> *def_gsi, tree def)
> gimple *square_use_stmt = USE_STMT (square_use_p);
> if (is_division_by (square_use_stmt, square_def))
> {
> - /* Halve the relative importance as this is called twice
> - for each division by a square. */
> + /* This is executed twice for each division by a square. */
> register_division_in (gimple_bb (square_use_stmt), 1);
> - square_recip_count ++;
> + square_recip_count++;
> }
> }
> }
> }
>
> - /* Square reciprocals will have been counted twice. */
> + /* Square reciprocals were counted twice above. */
> square_recip_count /= 2;
>
> + /* If it is more profitable to optimize 1 / x, don't optimize 1 / (x * x).
> */
> if (sqrt_recip_count > square_recip_count)
> - /* It will be more profitable to extract a 1 / x expression later,
> - so it is not worth attempting to extract 1 / (x * x) now. */
> return;
>
> /* Do the expensive part only if we can hope to optimize something. */
> - if (count + square_recip_count >= threshold
> - && count >= 1)
> + if (count + square_recip_count >= threshold && count >= 1)
> {
> gimple *use_stmt;
> for (occ = occ_head; occ; occ = occ->next)
> @@ -623,8 +623,7 @@ execute_cse_reciprocals_1 (gimple_stmt_iterator *def_gsi,
> tree def)
> FOR_EACH_IMM_USE_ON_STMT (use_p, use_iter)
> replace_reciprocal (use_p);
> }
> - else if (square_recip_count > 0
> - && is_square_of (use_stmt, def))
> + else if (square_recip_count > 0 && is_square_of (use_stmt, def))
> {
> FOR_EACH_IMM_USE_ON_STMT (use_p, use_iter)
> {
