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Re: [RFA] [PATCH] Minor improvement to canonicalization of COND_EXPR for gimple
- From: Richard Biener <richard dot guenther at gmail dot com>
- To: Jeff Law <law at redhat dot com>
- Cc: gcc-patches <gcc-patches at gcc dot gnu dot org>
- Date: Mon, 8 Apr 2013 11:12:15 +0200
- Subject: Re: [RFA] [PATCH] Minor improvement to canonicalization of COND_EXPR for gimple
- References: <51600373 dot 7050706 at redhat dot com>
On Sat, Apr 6, 2013 at 1:13 PM, Jeff Law <law@redhat.com> wrote:
>
>
> The tree combiner/forward propagator is missing opportunities to collapse
> sequences like this:
>
> _15 = _12 ^ _14;
> if (_15 != 0)
>
>
> Into:
>
> if (_12 != _14)
>
> The tree combiner/forward propagator builds this tree:
>
> x ^ y
>
> Then passes it to canonicalize_cond_expr_cond That is not suitable for the
> condition in a gimple COND_EXPR. So canonicalize_cond_expr_cond returns
> NULL. Thus combine_cond_expr_cond decides the tree it created isn't useful
> and throws it away.
>
> This patch changes canonicalize_cond_expr to rewrite x ^ y into x != y. The
> net result being the tree combiner/forward propagator is able to perform the
> desired simplification, eliminating the BIT_XOR_EXPR.
>
> Bootstrapped and regression tested on x86_64-unknown-linux-gnu. As you can
> see from the testcase, these kinds of sequences show up when compiling gcc
> itself.
>
> OK for the trunk?
Nice. Ok.
Thanks,
Richard.
> commit 809408a4bde6dfbaf62c5bda9ab7ae6c4447d984
> Author: Jeff Law <law@redhat.com>
> Date: Sat Apr 6 05:11:17 2013 -0600
>
> * gimple.c (canonicalize_cond_expr_cond): Rewrite x ^ y into
> x != y.
>
> * gcc.dg/tree-ssa/forwprop-25.c: New test
>
> diff --git a/gcc/ChangeLog b/gcc/ChangeLog
> index b8a6900..44797cc 100644
> --- a/gcc/ChangeLog
> +++ b/gcc/ChangeLog
> @@ -1,3 +1,8 @@
> +2013-04-06 Jeff Law <law@redhat.com>
> +
> + * gimple.c (canonicalize_cond_expr_cond): Rewrite x ^ y into
> + x != y.
> +
> 2013-04-03 Jeff Law <law@redhat.com>
>
> * Makefile.in (lra-constraints.o): Depend on $(OPTABS_H).
> diff --git a/gcc/gimple.c b/gcc/gimple.c
> index 785c2f0..cdb6f24 100644
> --- a/gcc/gimple.c
> +++ b/gcc/gimple.c
> @@ -2958,7 +2958,11 @@ canonicalize_cond_expr_cond (tree t)
> t = build2 (TREE_CODE (top0), TREE_TYPE (t),
> TREE_OPERAND (top0, 0), TREE_OPERAND (top0, 1));
> }
> -
> + /* For x ^ y use x != y. */
> + else if (TREE_CODE (t) == BIT_XOR_EXPR)
> + t = build2 (NE_EXPR, TREE_TYPE (t),
> + TREE_OPERAND (t, 0), TREE_OPERAND (t, 1));
> +
> if (is_gimple_condexpr (t))
> return t;
>
> diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
> index dc0b745..601ca66 100644
> --- a/gcc/testsuite/ChangeLog
> +++ b/gcc/testsuite/ChangeLog
> @@ -1,3 +1,7 @@
> +2013-04-06 Jeff Law <law@redhat.com>
> +
> + * gcc.dg/tree-ssa/forwprop-25.c: New test
> +
> 2013-04-03 Jeff Law <law@redhat.com>
>
> PR tree-optimization/56799
> diff --git a/gcc/testsuite/gcc.dg/tree-ssa/forwprop-25.c
> b/gcc/testsuite/gcc.dg/tree-ssa/forwprop-25.c
> new file mode 100644
> index 0000000..cf0c504
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/tree-ssa/forwprop-25.c
> @@ -0,0 +1,43 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O1 -fdump-tree-forwprop1" } */
> +
> +struct rtx_def;
> +typedef struct rtx_def *rtx;
> +typedef const struct rtx_def *const_rtx;
> +enum machine_mode
> +{
> + MAX_MACHINE_MODE,
> + NUM_MACHINE_MODES = MAX_MACHINE_MODE
> +};
> +extern const char *const mode_name[NUM_MACHINE_MODES];
> +enum mode_class
> +{ MODE_RANDOM, MODE_CC, MODE_INT, MODE_PARTIAL_INT, MODE_FRACT,
> MODE_UFRACT,
> + MODE_ACCUM, MODE_UACCUM, MODE_FLOAT, MODE_DECIMAL_FLOAT,
> MODE_COMPLEX_INT,
> + MODE_COMPLEX_FLOAT, MODE_VECTOR_INT, MODE_VECTOR_FRACT,
> + MODE_VECTOR_UFRACT, MODE_VECTOR_ACCUM, MODE_VECTOR_UACCUM,
> + MODE_VECTOR_FLOAT, MAX_MODE_CLASS };
> +extern const unsigned char mode_class[NUM_MACHINE_MODES];
> +extern const unsigned short mode_precision[NUM_MACHINE_MODES];
> +struct rtx_def
> +{
> + __extension__ enum machine_mode mode:8;
> +};
> +void
> +convert_move (rtx to, rtx from, int unsignedp)
> +{
> + enum machine_mode to_mode = ((enum machine_mode) (to)->mode);
> + enum machine_mode from_mode = ((enum machine_mode) (from)->mode);
> + ((void)
> + (!((mode_precision[from_mode] != mode_precision[to_mode])
> + || ((((enum mode_class) mode_class[from_mode]) == MODE_DECIMAL_FLOAT)
> !=
> + (((enum mode_class) mode_class[to_mode]) ==
> + MODE_DECIMAL_FLOAT))) ?
> + fancy_abort ("/home/gcc/virgin-gcc/gcc/expr.c", 380, __FUNCTION__),
> + 0 : 0));
> +}
> +
> +/* { dg-final { scan-tree-dump "Replaced.*!=.*with.*!=.* " "forwprop1"} }
> */
> +/* { dg-final { cleanup-tree-dump "forwprop1" } } */
> +
> +
> +
>