On Fri, May 31, 2013 at 10:18 PM, Jeff Law <l...@redhat.com> wrote:
>
> This is an implementation to fix a missed optimization pointed out to me by
> Kai.
>
> In all these examples, assume a & b are single bit types.
>
> ~a && b --> a < b
For a signed 1-bit type you'll have values -1, 0 and clearly
0 < -1
is false while ~0 & -1 is non-zero.
So I believe you have to restrict these transforms to signed 1-bit values
or adjust the folding appropriately. Besides that, ...
> a && ~b --> b < a
> ~a || b --> a <= b
> a && ~b --> b <= a
I wonder if these are really a simplification if the result is not used
exclusively in a conditional jump. Because for setting a register
to a < b you'll likely get worse code than using ~a & b (given that
many ISAs have a and-not instruction). Of course you may argue
that's a bug in the RTL / target piece (getting different code for
a < b vs. ~a & b) and a < b is shorter on the tree level.
More comments in-line.
> This happens with some regularity in GCC itself, though it's not as
> pervasive as some of the other missed optimizations I've run into.
>
> This could have gone into fold-const.c or tree-forwprop. fold-const.c
> isn't as useful as would need to see the entire expression as a single tree
> node. tree-forwprop.c can follow the use-def links and discover more
> opportunities even when the expressions span two source statements or are
> exposed by other optimizations.
>
> Bootstrapped and regression tested on x86_64-unknown-linux-gnu.
>
> OK for the trunk?
>
>
> commit 2b61de6f70576105fe6ada31618db23857f9c902
> Author: Jeff Law <l...@redhat.com>
> Date: Fri May 31 14:16:27 2013 -0600
>
> * tree-ssa-forwprop.c (simplify_bitwise_binary_boolean): New
> * function.
> (simplify_bitwise_binary): Use it to simpify certain binary ops
> on
> booleans.
>
> * gcc.dg/tree-ssa/forwprop-27.c: New test.
>
> diff --git a/gcc/ChangeLog b/gcc/ChangeLog
> index 396111e..7f027b0 100644
> --- a/gcc/ChangeLog
> +++ b/gcc/ChangeLog
> @@ -1,3 +1,9 @@
> +2013-05-31 Jeff Law <l...@redhat.com>
> +
> + * tree-ssa-forwprop.c (simplify_bitwise_binary_boolean): New
> function.
> + (simplify_bitwise_binary): Use it to simpify certain binary ops on
> + booleans.
> +
> 2013-05-28 Steve Ellcey <sell...@mips.com>
>
> * config/mips/mips-cpus.def (mips32r2): Change processor type.
> diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
> index 869371a..6f80afb 100644
> --- a/gcc/testsuite/ChangeLog
> +++ b/gcc/testsuite/ChangeLog
> @@ -1,3 +1,7 @@
> +2013-05-31 Jeff Law <l...@redhat.com>
> +
> + * gcc.dg/tree-ssa/forwprop-27.c: New test.
> +
> 2013-05-28 Balaji V. Iyer <balaji.v.i...@intel.com>
>
> * c-c++-common/cilk-plus/AN/array_test1.c: New test.
> diff --git a/gcc/testsuite/gcc.dg/tree-ssa/forwprop-27.c
> b/gcc/testsuite/gcc.dg/tree-ssa/forwprop-27.c
> new file mode 100644
> index 0000000..75e935d
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/tree-ssa/forwprop-27.c
> @@ -0,0 +1,78 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O2 -fdump-tree-forwprop1" } */
> +
> +extern char * frob (void);
> +extern _Bool testit(void);
> +
> +test (int code)
> +{
> + char * temp = frob();;
> + int rotate = (code == 22);
> + if (temp == 0 && !rotate)
> + oof();
> +}
> +
> +test_2 (int code)
> +{
> + char * temp = frob();
> + int rotate = (code == 22);
> + if (!rotate && temp == 0)
> + oof();
> +}
> +
> +
> +test_3 (int code)
> +{
> + char * temp = frob();
> + int rotate = (code == 22);
> + if (!rotate || temp == 0)
> + oof();
> +}
> +
> +
> +test_4 (int code)
> +{
> + char * temp = frob();
> + int rotate = (code == 22);
> + if (temp == 0 || !rotate)
> + oof();
> +}
> +
> +
> +test_5 (int code)
> +{
> + _Bool temp = testit();;
> + _Bool rotate = (code == 22);
> + if (temp == 0 && !rotate)
> + oof();
> +}
> +
> +test_6 (int code)
> +{
> + _Bool temp = testit();
> + _Bool rotate = (code == 22);
> + if (!rotate && temp == 0)
> + oof();
> +}
> +
> +
> +test_7 (int code)
> +{
> + _Bool temp = testit();
> + _Bool rotate = (code == 22);
> + if (!rotate || temp == 0)
> + oof();
> +}
> +
> +
> +test_8 (int code)
> +{
> + _Bool temp = testit();
> + _Bool rotate = (code == 22);
> + if (temp == 0 || !rotate)
> + oof();
> +}
> +
> +/* { dg-final { scan-tree-dump-times "Replaced" 8 "forwprop1"} } */
> +
> +
> diff --git a/gcc/tree-ssa-forwprop.c b/gcc/tree-ssa-forwprop.c
> index 6043d31..8c3f08b 100644
> --- a/gcc/tree-ssa-forwprop.c
> +++ b/gcc/tree-ssa-forwprop.c
> @@ -1870,6 +1870,45 @@ hoist_conversion_for_bitop_p (tree to, tree from)
> return false;
> }
>
> +/* GSI points to a statement of the form
> +
> + result = OP0 CODE OP1
> +
> + Where OP0 and OP1 are single bit SSA_NAMEs and CODE is either
> + BIT_AND_EXPR or BIT_IOR_EXPR.
> +
> + If OP0 is fed by a bitwise negation of another single bit SSA_NAME,
> + then we can simplify the two statements into a single LT_EXPR or LE_EXPR
> + when code is BIT_AND_EXPR and BIT_IOR_EXPR respectively.
> +
> + If a simplification is mode, return TRUE, else return FALSE. */
> +static bool
> +simplify_bitwise_binary_boolean (gimple_stmt_iterator *gsi,
> + enum tree_code code,
> + tree op0, tree op1)
> +{
> + gimple op0_def_stmt = SSA_NAME_DEF_STMT (op0);
> +
> + if (!is_gimple_assign (op0_def_stmt)
> + || (gimple_assign_rhs_code (op0_def_stmt) != BIT_NOT_EXPR))
> + return false;
> +
> + tree x = gimple_assign_rhs1 (op0_def_stmt);
> + if (TREE_CODE (x) == SSA_NAME
> + && INTEGRAL_TYPE_P (TREE_TYPE (x))
> + && TYPE_PRECISION (TREE_TYPE (x)) == 1)
Do these transforms not work for BOOLEAN_TYPE as well?
> + {
> + gimple stmt = gsi_stmt (*gsi);
> + gimple_assign_set_rhs1 (stmt, x);
> + gimple_assign_set_rhs2 (stmt, op1);
> + gimple_assign_set_rhs_code (stmt, code == BIT_AND_EXPR ? LT_EXPR :
> LE_EXPR);
> + update_stmt (gsi_stmt (*gsi));
No need to query gsi_stmt again, it cannot change.
> + return true;
> + }
> + return false;
> +
> +}
> +
> /* Simplify bitwise binary operations.
> Return true if a transformation applied, otherwise return false. */
>
> @@ -2118,8 +2157,26 @@ simplify_bitwise_binary (gimple_stmt_iterator *gsi)
> return true;
> }
> }
> - }
>
> + /* If arg1 and arg2 are booleans (or any single bit type)
> + then try to simplify:
> +
> + (~X & Y) -> X < Y
> + (X & ~Y) -> Y < X
> + (~X | Y) -> X <= Y
> + (X | ~Y) -> Y <= X */
> + if (TREE_CODE (arg1) == SSA_NAME
> + && TREE_CODE (arg2) == SSA_NAME
> + && INTEGRAL_TYPE_P (TREE_TYPE (arg1))
> + && TYPE_PRECISION (TREE_TYPE (arg1)) == 1
> + && TYPE_PRECISION (TREE_TYPE (arg2)) == 1)
> + {
> + if (simplify_bitwise_binary_boolean (gsi, code, arg1, arg2))
> + return true;
> + if (simplify_bitwise_binary_boolean (gsi, code, arg2, arg1))
> + return true;
> + }
> + }
> return false;
> }
>
>
