Hi Jeff,
On 10 October 2016 at 23:06, Jeff Law <l...@redhat.com> wrote:
>
>
> So if we have an equality conditional between A & B, we record into our
> const/copy tables A = B and B = A.
>
> This helps us discover some of the more obscure equivalences. But it also
> creates problems with an expression like
>
> A ^ B
>
> Where we might cprop the first operand generating
>
> B ^ B
>
> Then the second generating
>
> B ^ A
>
> ANd we've lost the folding opportunity. At first I'd tried folding after
> each propagation step, but that turns into a bit of a nightmare because of
> changes in the underlying structure of the gimple statement and cycles that
> may develop if we re-build the operand cache after folding.
>
> This approach is simpler and should catch all these cases for binary
> operators. We just track the last copy propagated argument and refuse to
> ping-pong propagations.
>
> It fixes the tests from 71947 and 77647 without regressing (obviously). I've
> included an xfailed test for a more complex situation that we don't
> currently handle (would require backtracking from the equality comparison
> through the logicals that feed the equality comparison).
>
FWIW, this test is XPASS on arm-none-linux-gnueabihf
--with-cpu=cortex-a5 --with-fpu=vfpv3-d16-fp16:
Christophe
> Bootstrapped and regression tested on x86_64. Applied to the trunk.
>
>
> commit 6223e6e425b6de916f0330b9dbe5698765d4a73c
> Author: law <law@138bc75d-0d04-0410-961f-82ee72b054a4>
> Date: Mon Oct 10 20:40:59 2016 +0000
>
> PR tree-optimization/71947
> * tree-ssa-dom.c (cprop_into_stmt): Avoid replacing A with B, then
> B with A within a single statement.
>
> PR tree-optimization/71947
> * gcc.dg/tree-ssa/pr71947-1.c: New test.
> * gcc.dg/tree-ssa/pr71947-2.c: New test.
> * gcc.dg/tree-ssa/pr71947-3.c: New test.
> * gcc.dg/tree-ssa/pr71947-4.c: New test.
> * gcc.dg/tree-ssa/pr71947-5.c: New test.
> * gcc.dg/tree-ssa/pr71947-6.c: New test.
>
> git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@240947
> 138bc75d-0d04-0410-961f-82ee72b054a4
>
> diff --git a/gcc/ChangeLog b/gcc/ChangeLog
> index 1738bc7..16e25bf 100644
> --- a/gcc/ChangeLog
> +++ b/gcc/ChangeLog
> @@ -1,3 +1,9 @@
> +2016-10-10 Jeff Law <l...@redhat.com>
> +
> + PR tree-optimization/71947
> + * tree-ssa-dom.c (cprop_into_stmt): Avoid replacing A with B, then
> + B with A within a single statement.
> +
> 2016-10-10 Bill Schmidt <wschm...@linux.vnet.ibm.com>
>
> PR tree-optimization/77824
> diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
> index 04966cf..e31bcc6 100644
> --- a/gcc/testsuite/ChangeLog
> +++ b/gcc/testsuite/ChangeLog
> @@ -1,3 +1,13 @@
> +2016-10-10 Jeff Law <l...@redhat.com>
> +
> + PR tree-optimization/71947
> + * gcc.dg/tree-ssa/pr71947-1.c: New test.
> + * gcc.dg/tree-ssa/pr71947-2.c: New test.
> + * gcc.dg/tree-ssa/pr71947-3.c: New test.
> + * gcc.dg/tree-ssa/pr71947-4.c: New test.
> + * gcc.dg/tree-ssa/pr71947-5.c: New test.
> + * gcc.dg/tree-ssa/pr71947-6.c: New test.
> +
> 2016-10-10 Thomas Koenig <tkoe...@gcc.gnu.org>
>
> PR fortran/77915
> diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr71947-1.c
> b/gcc/testsuite/gcc.dg/tree-ssa/pr71947-1.c
> new file mode 100644
> index 0000000..b033495
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/tree-ssa/pr71947-1.c
> @@ -0,0 +1,19 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O2 -fno-tree-vrp -fdump-tree-dom-details" } */
> +
> +
> +int f(int x, int y)
> +{
> + int ret;
> +
> + if (x == y)
> + ret = x ^ y;
> + else
> + ret = 1;
> +
> + return ret;
> +}
> +
> +/* { dg-final { scan-tree-dump "Folded to: ret_\[0-9\]+ = 0;" "dom2" } }
> */
> +
> +
> diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr71947-2.c
> b/gcc/testsuite/gcc.dg/tree-ssa/pr71947-2.c
> new file mode 100644
> index 0000000..de8f88b
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/tree-ssa/pr71947-2.c
> @@ -0,0 +1,16 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O2 -fno-tree-vrp -fdump-tree-dom-details" } */
> +
> +
> +int f(int x, int y)
> +{
> + int ret;
> + if (x == y)
> + ret = x - y;
> + else
> + ret = 1;
> +
> + return ret;
> +}
> +
> +/* { dg-final { scan-tree-dump "Folded to: ret_\[0-9\]+ = 0;" "dom2" } }
> */
> diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr71947-3.c
> b/gcc/testsuite/gcc.dg/tree-ssa/pr71947-3.c
> new file mode 100644
> index 0000000..e79847f
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/tree-ssa/pr71947-3.c
> @@ -0,0 +1,12 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O2 -fno-tree-vrp -fdump-tree-dom-details" } */
> +
> +int f(int x, int y)
> +{
> + int ret = 10;
> + if (x == y)
> + ret = x - y;
> + return ret;
> +}
> +
> +/* { dg-final { scan-tree-dump "Folded to: ret_\[0-9\]+ = 0;" "dom2" } }
> */
> diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr71947-4.c
> b/gcc/testsuite/gcc.dg/tree-ssa/pr71947-4.c
> new file mode 100644
> index 0000000..a881f0d
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/tree-ssa/pr71947-4.c
> @@ -0,0 +1,22 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O2 -fno-tree-vrp -fdump-tree-dom-details" } */
> +
> +
> +
> +static inline long load(long *p)
> +{
> + long ret;
> + asm ("movq %1,%0\n\t" : "=r" (ret) : "m" (*p));
> + if (ret != *p)
> + __builtin_unreachable();
> + return ret;
> +}
> +
> +long foo(long *mem)
> +{
> + long ret;
> + ret = load(mem);
> + return ret + *mem;
> +}
> +
> +/* { dg-final { scan-tree-dump "Folded to: _\[0-9\]+ = _\[0-9\]+ \\* 2"
> "dom2" } } */
> diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr71947-5.c
> b/gcc/testsuite/gcc.dg/tree-ssa/pr71947-5.c
> new file mode 100644
> index 0000000..fa679f0
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/tree-ssa/pr71947-5.c
> @@ -0,0 +1,21 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O2 -fno-tree-vrp -fdump-tree-dom-details" } */
> +
> +
> +static inline long load(long *p)
> +{
> + long ret;
> + asm ("movq %1,%0\n\t" : "=r" (ret) : "m" (*p));
> + if (ret != *p)
> + __builtin_unreachable();
> + return ret;
> +}
> +
> +long foo(long *mem)
> +{
> + long ret;
> + ret = load(mem);
> + return ret - *mem;
> +}
> +
> +/* { dg-final { scan-tree-dump "Folded to: _\[0-9\]+ = 0;" "dom2" } } */
> diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr71947-6.c
> b/gcc/testsuite/gcc.dg/tree-ssa/pr71947-6.c
> new file mode 100644
> index 0000000..9cb89cb
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/tree-ssa/pr71947-6.c
> @@ -0,0 +1,16 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O2 -fno-tree-vrp -fdump-tree-dom-details" } */
> +
> +
> +int f(int x, int y, int a, int b)
> +{
> + int ret = 10;
> + if (a == x
> + && b == y
> + && a == b)
> + ret = x - y;
> +
> + return ret;
> +}
> +
> +/* { dg-final { scan-tree-dump "Folded to: ret_\[0-9\]+ = 0;" "dom2" {
> xfail *-*-* } } } */
> diff --git a/gcc/tree-ssa-dom.c b/gcc/tree-ssa-dom.c
> index b007388..5376ff9 100644
> --- a/gcc/tree-ssa-dom.c
> +++ b/gcc/tree-ssa-dom.c
> @@ -1731,9 +1731,26 @@ cprop_into_stmt (gimple *stmt)
> {
> use_operand_p op_p;
> ssa_op_iter iter;
> + tree last_copy_propagated_op = NULL;
>
> FOR_EACH_SSA_USE_OPERAND (op_p, stmt, iter, SSA_OP_USE)
> - cprop_operand (stmt, op_p);
> + {
> + tree old_op = USE_FROM_PTR (op_p);
> +
> + /* If we have A = B and B = A in the copy propagation tables
> + (due to an equality comparison), avoid substituting B for A
> + then A for B in the trivially discovered cases. This allows
> + optimization of statements were A and B appear as input
> + operands. */
> + if (old_op != last_copy_propagated_op)
> + {
> + cprop_operand (stmt, op_p);
> +
> + tree new_op = USE_FROM_PTR (op_p);
> + if (new_op != old_op && TREE_CODE (new_op) == SSA_NAME)
> + last_copy_propagated_op = new_op;
> + }
> + }
> }
>
> /* Optimize the statement in block BB pointed to by iterator SI
>
