Re: [PATCH V6] Remove empty loop with assumed finiteness (PR tree-optimization/89713)
On Tue, Jun 4, 2019 at 5:24 PM Feng Xue OS wrote:
>
> Some changes on documentation.
Please name the option -ffinite-loops (plural), the patch is OK with this
change if you also adjust
> + /* If the loop has any non-EH exit, we can assume it will terminate. */
> + FOR_EACH_VEC_ELT (exits, i, ex)
> + if (!(ex->flags & EDGE_EH))
> + {
to look for "normal" edges only - in addition to EDGE_EH you
want to ignore EDGE_FAKE and EDGE_ABNORMAL. EDGE_FAKE
are inserted by connect_infiinite_loops_to_exit and EDGE_ABNORMAL
can appear with setjmp/longjmp and friends.
I think this change also warrants mentioning in gcc-10/changes.html.
Thanks,
Richard.
> Feng
>
>
> diff --git a/gcc/ChangeLog b/gcc/ChangeLog
> index 37aab79..4fdc5c8 100644
> --- a/gcc/ChangeLog
> +++ b/gcc/ChangeLog
> @@ -1,3 +1,16 @@
> +2019-06-04 Feng Xue
> +
> + PR tree-optimization/89713
> + * doc/invoke.texi (-ffinite-loop): Document new option.
> + * common.opt (-ffinite-loop): New option.
> + * tree-ssa-dce.c (mark_stmt_if_obviously_necessary): Mark
> + IFN_GOACC_LOOP calls as necessary.
> + * tree-ssa-loop-niter.c (finite_loop): Assume loop with an exit is
> + finite.
> + * omp-offload.c (oacc_xform_loop): Skip lowering if return value of
> + IFN_GOACC_LOOP call is not used.
> + * opts.c (default_options_table): Enable -ffinite-loop at -O2+.
> +
> 2019-06-04 Alan Modra
>
> PR target/90689
> diff --git a/gcc/common.opt b/gcc/common.opt
> index 0e72fd0..f570815 100644
> --- a/gcc/common.opt
> +++ b/gcc/common.opt
> @@ -1437,6 +1437,10 @@ ffinite-math-only
> Common Report Var(flag_finite_math_only) Optimization SetByCombined
> Assume no NaNs or infinities are generated.
>
> +ffinite-loop
> +Common Report Var(flag_finite_loop) Optimization
> +Assume that loops with an exit will terminate and not loop indefinitely.
> +
> ffixed-
> Common Joined RejectNegative Var(common_deferred_options) Defer
> -ffixed- Mark as being unavailable to the compiler.
> diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
> index 91c9bb8..2cb0b9a 100644
> --- a/gcc/doc/invoke.texi
> +++ b/gcc/doc/invoke.texi
> @@ -412,6 +412,7 @@ Objective-C and Objective-C++ Dialects}.
> -fdevirtualize-at-ltrans -fdse @gol
> -fearly-inlining -fipa-sra -fexpensive-optimizations -ffat-lto-objects
> @gol
> -ffast-math -ffinite-math-only -ffloat-store
> -fexcess-precision=@var{style} @gol
> +-ffinite-loop @gol
> -fforward-propagate -ffp-contract=@var{style} -ffunction-sections @gol
> -fgcse -fgcse-after-reload -fgcse-las -fgcse-lm -fgraphite-identity @gol
> -fgcse-sm -fhoist-adjacent-loads -fif-conversion @gol
> @@ -8282,6 +8283,7 @@ also turns on the following optimization flags:
> -fdelete-null-pointer-checks @gol
> -fdevirtualize -fdevirtualize-speculatively @gol
> -fexpensive-optimizations @gol
> +-ffinite-loop @gol
> -fgcse -fgcse-lm @gol
> -fhoist-adjacent-loads @gol
> -finline-small-functions @gol
> @@ -9503,6 +9505,15 @@ that may set @code{errno} but are otherwise free of
> side effects. This flag is
> enabled by default at @option{-O2} and higher if @option{-Os} is not also
> specified.
>
> +@item -ffinite-loop
> +@opindex ffinite-loop
> +@opindex fno-finite-loop
> +Assume that a loop with an exit will eventually take the exit and not loop
> +indefinitely. This allows the compiler to remove loops that otherwise have
> +no side-effects, not considering eventual endless looping as such.
> +
> +This option is enabled by default at @option{-O2}.
> +
> @item -ftree-dominator-opts
> @opindex ftree-dominator-opts
> Perform a variety of simple scalar cleanups (constant/copy
> diff --git a/gcc/omp-offload.c b/gcc/omp-offload.c
> index 97ae47b..369122f 100644
> --- a/gcc/omp-offload.c
> +++ b/gcc/omp-offload.c
> @@ -300,7 +300,7 @@ oacc_xform_loop (gcall *call)
>tree chunk_size = NULL_TREE;
>unsigned mask = (unsigned) TREE_INT_CST_LOW (gimple_call_arg (call, 5));
>tree lhs = gimple_call_lhs (call);
> - tree type = TREE_TYPE (lhs);
> + tree type = NULL_TREE;
>tree diff_type = TREE_TYPE (range);
>tree r = NULL_TREE;
>gimple_seq seq = NULL;
> @@ -308,6 +308,15 @@ oacc_xform_loop (gcall *call)
>unsigned outer_mask = mask & (~mask + 1); // Outermost partitioning
>unsigned inner_mask = mask & ~outer_mask; // Inner partitioning (if any)
>
> + /* Skip lowering if return value of IFN_GOACC_LOOP call is not used. */
> + if (!lhs)
> +{
> + gsi_replace_with_seq (&gsi, seq, true);
> + return;
> +}
> +
> + type = TREE_TYPE (lhs);
> +
> #ifdef ACCEL_COMPILER
>chunk_size = gimple_call_arg (call, 4);
>if (integer_minus_onep (chunk_size) /* Force static allocation. */
> diff --git a/gcc/opts.c b/gcc/opts.c
> index 64f94ac..0db9dda 100644
> --- a/gcc/opts.c
> +++ b/gcc/opts.c
> @@ -494,6 +494,7 @@ static const struct default_options
> default_options_table[] =
> { OPT_LEVELS_2_PLUS
[PATCH V6] Remove empty loop with assumed finiteness (PR tree-optimization/89713)
Some changes on documentation.
Feng
diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 37aab79..4fdc5c8 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,16 @@
+2019-06-04 Feng Xue
+
+ PR tree-optimization/89713
+ * doc/invoke.texi (-ffinite-loop): Document new option.
+ * common.opt (-ffinite-loop): New option.
+ * tree-ssa-dce.c (mark_stmt_if_obviously_necessary): Mark
+ IFN_GOACC_LOOP calls as necessary.
+ * tree-ssa-loop-niter.c (finite_loop): Assume loop with an exit is
+ finite.
+ * omp-offload.c (oacc_xform_loop): Skip lowering if return value of
+ IFN_GOACC_LOOP call is not used.
+ * opts.c (default_options_table): Enable -ffinite-loop at -O2+.
+
2019-06-04 Alan Modra
PR target/90689
diff --git a/gcc/common.opt b/gcc/common.opt
index 0e72fd0..f570815 100644
--- a/gcc/common.opt
+++ b/gcc/common.opt
@@ -1437,6 +1437,10 @@ ffinite-math-only
Common Report Var(flag_finite_math_only) Optimization SetByCombined
Assume no NaNs or infinities are generated.
+ffinite-loop
+Common Report Var(flag_finite_loop) Optimization
+Assume that loops with an exit will terminate and not loop indefinitely.
+
ffixed-
Common Joined RejectNegative Var(common_deferred_options) Defer
-ffixed- Mark as being unavailable to the compiler.
diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index 91c9bb8..2cb0b9a 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -412,6 +412,7 @@ Objective-C and Objective-C++ Dialects}.
-fdevirtualize-at-ltrans -fdse @gol
-fearly-inlining -fipa-sra -fexpensive-optimizations -ffat-lto-objects @gol
-ffast-math -ffinite-math-only -ffloat-store -fexcess-precision=@var{style}
@gol
+-ffinite-loop @gol
-fforward-propagate -ffp-contract=@var{style} -ffunction-sections @gol
-fgcse -fgcse-after-reload -fgcse-las -fgcse-lm -fgraphite-identity @gol
-fgcse-sm -fhoist-adjacent-loads -fif-conversion @gol
@@ -8282,6 +8283,7 @@ also turns on the following optimization flags:
-fdelete-null-pointer-checks @gol
-fdevirtualize -fdevirtualize-speculatively @gol
-fexpensive-optimizations @gol
+-ffinite-loop @gol
-fgcse -fgcse-lm @gol
-fhoist-adjacent-loads @gol
-finline-small-functions @gol
@@ -9503,6 +9505,15 @@ that may set @code{errno} but are otherwise free of side
effects. This flag is
enabled by default at @option{-O2} and higher if @option{-Os} is not also
specified.
+@item -ffinite-loop
+@opindex ffinite-loop
+@opindex fno-finite-loop
+Assume that a loop with an exit will eventually take the exit and not loop
+indefinitely. This allows the compiler to remove loops that otherwise have
+no side-effects, not considering eventual endless looping as such.
+
+This option is enabled by default at @option{-O2}.
+
@item -ftree-dominator-opts
@opindex ftree-dominator-opts
Perform a variety of simple scalar cleanups (constant/copy
diff --git a/gcc/omp-offload.c b/gcc/omp-offload.c
index 97ae47b..369122f 100644
--- a/gcc/omp-offload.c
+++ b/gcc/omp-offload.c
@@ -300,7 +300,7 @@ oacc_xform_loop (gcall *call)
tree chunk_size = NULL_TREE;
unsigned mask = (unsigned) TREE_INT_CST_LOW (gimple_call_arg (call, 5));
tree lhs = gimple_call_lhs (call);
- tree type = TREE_TYPE (lhs);
+ tree type = NULL_TREE;
tree diff_type = TREE_TYPE (range);
tree r = NULL_TREE;
gimple_seq seq = NULL;
@@ -308,6 +308,15 @@ oacc_xform_loop (gcall *call)
unsigned outer_mask = mask & (~mask + 1); // Outermost partitioning
unsigned inner_mask = mask & ~outer_mask; // Inner partitioning (if any)
+ /* Skip lowering if return value of IFN_GOACC_LOOP call is not used. */
+ if (!lhs)
+{
+ gsi_replace_with_seq (&gsi, seq, true);
+ return;
+}
+
+ type = TREE_TYPE (lhs);
+
#ifdef ACCEL_COMPILER
chunk_size = gimple_call_arg (call, 4);
if (integer_minus_onep (chunk_size) /* Force static allocation. */
diff --git a/gcc/opts.c b/gcc/opts.c
index 64f94ac..0db9dda 100644
--- a/gcc/opts.c
+++ b/gcc/opts.c
@@ -494,6 +494,7 @@ static const struct default_options default_options_table[]
=
{ OPT_LEVELS_2_PLUS, OPT_fdevirtualize, NULL, 1 },
{ OPT_LEVELS_2_PLUS, OPT_fdevirtualize_speculatively, NULL, 1 },
{ OPT_LEVELS_2_PLUS, OPT_fexpensive_optimizations, NULL, 1 },
+{ OPT_LEVELS_2_PLUS, OPT_ffinite_loop, NULL, 1 },
{ OPT_LEVELS_2_PLUS, OPT_fgcse, NULL, 1 },
{ OPT_LEVELS_2_PLUS, OPT_fhoist_adjacent_loads, NULL, 1 },
{ OPT_LEVELS_2_PLUS, OPT_findirect_inlining, NULL, 1 },
diff --git a/gcc/testsuite/g++.dg/tree-ssa/empty-loop.C
b/gcc/testsuite/g++.dg/tree-ssa/empty-loop.C
new file mode 100644
index 000..e374155
--- /dev/null
+++ b/gcc/testsuite/g++.dg/tree-ssa/empty-loop.C
@@ -0,0 +1,33 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-cddce2 -ffinite-loop" } */
+
+#include
+#include
+#include
+#include
+#include
+
+using namespace std;
+
+int foo (vector &v, list &l, set &s, map
&m)
+{
+ for (vector::iterat
