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Re: [PATCH] Allow non-overflow ops in vect_is_simple_reduction_1
- From: Tom de Vries <Tom_deVries at mentor dot com>
- To: Richard Biener <richard dot guenther at gmail dot com>
- Cc: "gcc-patches at gnu dot org" <gcc-patches at gnu dot org>
- Date: Wed, 29 Jul 2015 13:22:00 +0200
- Subject: Re: [PATCH] Allow non-overflow ops in vect_is_simple_reduction_1
- Authentication-results: sourceware.org; auth=none
- References: <55B24E1F dot 1070705 at mentor dot com> <CAFiYyc1-F5cx760mQFr6D1gByhz2n0cpfLMdNGkMfU-i=DN0LA at mail dot gmail dot com> <55B770A1 dot 6010308 at mentor dot com> <CAFiYyc3ahG0gzkfXxdjig-V2SJijV_UPaQJd0hORv5i93qSi4A at mail dot gmail dot com>
On 29/07/15 10:09, Richard Biener wrote:
On Tue, Jul 28, 2015 at 2:08 PM, Tom de Vries <Tom_deVries@mentor.com> wrote:
On 28/07/15 09:59, Richard Biener wrote:
On Fri, Jul 24, 2015 at 4:39 PM, Tom de Vries <Tom_deVries@mentor.com>
wrote:
Hi,
this patch allows parallelization and vectorization of reduction
operators
that are guaranteed to not overflow (such as min and max operators),
independent of the overflow behaviour of the type.
Bootstrapped and reg-tested on x86_64.
OK for trunk?
Hmm, I don't like that no_overflow_tree_code function. We have a much
more
clear understanding which codes may overflow or trap. Thus please add
a operation specific variant of TYPE_OVERFLOW_{TRAPS,WRAPS,UNDEFINED} like
Done.
bool
operation_overflow_traps (tree type, enum tree_code code)
{
if (!ANY_INTEGRAL_TYPE_P (type)
I've changed this test into a gcc_checking_assert.
|| !TYPE_OVERFLOW_TRAPS (type))
return false;
switch (code)
{
case PLUS_EXPR:
case MINUS_EXPR:
case MULT_EXPR:
case LSHIFT_EXPR:
/* Can overflow in various ways */
case TRUNC_DIV_EXPR:
case EXACT_DIV_EXPR:
case FLOOR_DIV_EXPR:
case CEIL_DIV_EXPR:
/* For INT_MIN / -1 */
case NEGATE_EXPR:
case ABS_EXPR:
/* For -INT_MIN */
return true;
default:
return false;
}
}
and similar variants for _wraps and _undefined. I think we decided at
some point
the compiler should not take advantage of the fact that lshift or
*_div have undefined
behavior on signed integer overflow, similar we only take advantage of
integral-type
overflow behavior, not vector or complex. So we could reduce the
number of cases
the functions return true if we document that it returns true only for
the cases where
the compiler needs to / may assume wrapping behavior does not take place.
As for _traps for example we only have optabs and libfuncs for
plus,minus,mult,negate
and abs.
I've tried to capture all of this in the three new functions:
- operation_overflows_and_traps
- operation_no_overflow_or_wraps
- operation_overflows_and_undefined (unused atm)
I've also added the graphite bit.
OK for trunk, if bootstrap and reg-test succeeds?
+/* Returns true if CODE operating on operands of type TYPE can overflow, and
+ fwrapv generates trapping insns for CODE. */
ftrapv
Done.
+bool
+operation_overflows_and_traps (tree type, enum tree_code code)
+{
operation_overflow_traps
is better wording. Meaning that when the operation overflows then it traps.
AFAIU, the purpose of the function is to enable optimizations when it
returns false, that is:
- if the operation doesn't overflow, or
- if the operation overflows, but doesn't trap.
The name operation_overflow_traps does not make clear what it returns
when the operation doesn't overflow. If the name doesn't make it clear,
you need to be conservative, that is, return true. Which defies the
purpose of the function.
I've changed the name to operation_no_trapping_overflow (and inverted
logic in the function).
But perhaps you want operation_overflow_traps with a conservative return
for non-overflow operations, and use it like this:
...
else if (INTEGRAL_TYPE_P (type) && check_reduction)
{
if (operation_overflows (type, code)
&& operation_overflow_traps (type, code))
{
/* Changing the order of operations changes the semantics. */
...
?
+ /* We don't take advantage of integral type overflow behaviour for
complex and
+ vector types. */
We don't generate instructions that trap on overflow for complex or vector types
Done.
+ if (!INTEGRAL_TYPE_P (type))
+ return true;
+ switch (code)
+ {
+ case PLUS_EXPR:
+ case MINUS_EXPR:
+ case MULT_EXPR:
+ case LSHIFT_EXPR:
+ /* Can overflow in various ways. */
we don't have a trapping optab for lshift
+ case TRUNC_DIV_EXPR:
+ case EXACT_DIV_EXPR:
+ case FLOOR_DIV_EXPR:
+ case CEIL_DIV_EXPR:
nor division. See optabs.c:optab_for_tree_code. I suggest to only return true
for those.
Before the logic inversion, we return false for these (And also for
operators that do not overflow).
+/* Returns true if CODE operating on operands of type TYPE cannot overflow, or
+ wraps on overflow. */
+
+bool
+operation_no_overflow_or_wraps (tree type, enum tree_code code)
+{
+ gcc_checking_assert (ANY_INTEGRAL_TYPE_P (type));
operation_overflow_wraps ()
is still my preferred name.
The name operation_overflow_wraps doesn't make clear what it returns if
the operation doesn't overflow. And I didn't manage to come up with a
better name sofar.
Btw, I wonder about something like vector max operation. The current
implementation of operation_no_overflow_or_wraps returns false. Could we do:
...
/* We don't take advantage of integral type overflow behaviour for
complex and vector types. */
if (!INTEGRAL_TYPE_P (type))
return !operation_overflows (type, code);
...
?
+bool
+operation_overflow_and_undefined (tree type, enum tree_code code)
+{
+ gcc_checking_assert (ANY_INTEGRAL_TYPE_P (type));
+
operation_overflow_undefined ()
The name operation_overflow_undefined doesn't make clear what it returns
if the operation doesn't overflow. I've changed it into
operation_undefined_overflow.
If you like to keep an explicit operation_can_overflow then there is the
opportunity to split out the switch statement from operation_overflow_wraps
and operation_overflow_undefined.
Done.
OK for trunk if bootstrap and reg-test succeeds?
Thanks,
- Tom
Allow non-overflow ops in reductions
2015-07-28 Tom de Vries <tom@codesourcery.com>
* tree.c (operations_overflows, operation_no_trapping_overflow)
(operation_no_overflow_or_wraps, operation_undefined_overflow): New
function.
* tree.h (operations_overflows, operation_no_trapping_overflow)
(operation_no_overflow_or_wraps, operation_undefined_overflow): Declare.
* tree-vect-loop.c (vect_is_simple_reduction_1): Use
operation_no_trapping_overflow and operation_no_overflow_or_wraps.
* graphite-sese-to-poly.c (is_reduction_operation_p): Use
operation_no_overflow_or_wraps.
* gcc.dg/autopar/reduc-2char.c (init_arrays): Mark with attribute
optimize ("-ftree-parallelize-loops=0").
Add successful scans for 2 detected reductions. Add xfail scans for 3
detected reductions.
* gcc.dg/autopar/reduc-2short.c: Same.
* gcc.dg/autopar/reduc-8.c (init_arrays): Mark with attribute
optimize ("-ftree-parallelize-loops=0"). Add successful scans for 2
detected reductions.
* gcc.dg/vect/trapv-vect-reduc-4.c: Update scan to match vectorized min
and max reductions.
---
gcc/graphite-sese-to-poly.c | 6 +-
gcc/testsuite/gcc.dg/autopar/reduc-2char.c | 10 +-
gcc/testsuite/gcc.dg/autopar/reduc-2short.c | 10 +-
gcc/testsuite/gcc.dg/autopar/reduc-8.c | 7 +-
gcc/testsuite/gcc.dg/vect/trapv-vect-reduc-4.c | 2 +-
gcc/tree-vect-loop.c | 5 +-
gcc/tree.c | 127 +++++++++++++++++++++++++
gcc/tree.h | 4 +
8 files changed, 156 insertions(+), 15 deletions(-)
diff --git a/gcc/graphite-sese-to-poly.c b/gcc/graphite-sese-to-poly.c
index c583f16..b57dc9c 100644
--- a/gcc/graphite-sese-to-poly.c
+++ b/gcc/graphite-sese-to-poly.c
@@ -2614,8 +2614,10 @@ is_reduction_operation_p (gimple stmt)
if (FLOAT_TYPE_P (type))
return flag_associative_math;
- return (INTEGRAL_TYPE_P (type)
- && TYPE_OVERFLOW_WRAPS (type));
+ if (ANY_INTEGRAL_TYPE_P (type))
+ return operation_no_overflow_or_wraps (type, code);
+
+ return false;
}
/* Returns true when PHI contains an argument ARG. */
diff --git a/gcc/testsuite/gcc.dg/autopar/reduc-2char.c b/gcc/testsuite/gcc.dg/autopar/reduc-2char.c
index 14867f3..a2dad44 100644
--- a/gcc/testsuite/gcc.dg/autopar/reduc-2char.c
+++ b/gcc/testsuite/gcc.dg/autopar/reduc-2char.c
@@ -39,8 +39,9 @@ void main1 (signed char x, signed char max_result, signed char min_result)
abort ();
}
- __attribute__((noinline))
- void init_arrays ()
+void __attribute__((noinline))
+ __attribute__((optimize ("-ftree-parallelize-loops=0")))
+init_arrays ()
{
int i;
@@ -60,7 +61,10 @@ int main (void)
}
-/* { dg-final { scan-tree-dump-times "Detected reduction" 2 "parloops" { xfail *-*-* } } } */
+/* { dg-final { scan-tree-dump-times "Detected reduction" 2 "parloops" } } */
+/* { dg-final { scan-tree-dump-times "Detected reduction" 3 "parloops" { xfail *-*-* } } } */
+
+/* { dg-final { scan-tree-dump-times "SUCCESS: may be parallelized" 2 "parloops" } } */
/* { dg-final { scan-tree-dump-times "SUCCESS: may be parallelized" 3 "parloops" { xfail *-*-* } } } */
diff --git a/gcc/testsuite/gcc.dg/autopar/reduc-2short.c b/gcc/testsuite/gcc.dg/autopar/reduc-2short.c
index 7c19cc5..a50e14f 100644
--- a/gcc/testsuite/gcc.dg/autopar/reduc-2short.c
+++ b/gcc/testsuite/gcc.dg/autopar/reduc-2short.c
@@ -38,8 +38,9 @@ void main1 (short x, short max_result, short min_result)
abort ();
}
- __attribute__((noinline))
- void init_arrays ()
+void __attribute__((noinline))
+ __attribute__((optimize ("-ftree-parallelize-loops=0")))
+init_arrays ()
{
int i;
@@ -58,7 +59,8 @@ int main (void)
return 0;
}
+/* { dg-final { scan-tree-dump-times "Detected reduction" 2 "parloops" } } */
+/* { dg-final { scan-tree-dump-times "Detected reduction" 3 "parloops" { xfail *-*-* } } } */
-/* { dg-final { scan-tree-dump-times "Detected reduction" 2 "parloops" { xfail *-*-* } } } */
+/* { dg-final { scan-tree-dump-times "SUCCESS: may be parallelized" 2 "parloops" } } */
/* { dg-final { scan-tree-dump-times "SUCCESS: may be parallelized" 3 "parloops" { xfail *-*-* } } } */
-
diff --git a/gcc/testsuite/gcc.dg/autopar/reduc-8.c b/gcc/testsuite/gcc.dg/autopar/reduc-8.c
index 1d05c48..18ba03d 100644
--- a/gcc/testsuite/gcc.dg/autopar/reduc-8.c
+++ b/gcc/testsuite/gcc.dg/autopar/reduc-8.c
@@ -40,7 +40,8 @@ testmin (const T *c, T init, T result)
abort ();
}
-int main (void)
+int __attribute__((optimize ("-ftree-parallelize-loops=0")))
+main (void)
{
static signed char A[N] = {
0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08,
@@ -84,5 +85,5 @@ int main (void)
}
-/* { dg-final { scan-tree-dump-times "Detected reduction" 2 "parloops" { xfail *-*-* } } } */
-/* { dg-final { scan-tree-dump-times "SUCCESS: may be parallelized" 3 "parloops" { xfail *-*-* } } } */
+/* { dg-final { scan-tree-dump-times "Detected reduction" 2 "parloops" } } */
+/* { dg-final { scan-tree-dump-times "SUCCESS: may be parallelized" 2 "parloops" } } */
diff --git a/gcc/testsuite/gcc.dg/vect/trapv-vect-reduc-4.c b/gcc/testsuite/gcc.dg/vect/trapv-vect-reduc-4.c
index 2129717..86f9b90 100644
--- a/gcc/testsuite/gcc.dg/vect/trapv-vect-reduc-4.c
+++ b/gcc/testsuite/gcc.dg/vect/trapv-vect-reduc-4.c
@@ -46,4 +46,4 @@ int main (void)
return 0;
}
-/* { dg-final { scan-tree-dump-times "vectorized 0 loops" 1 "vect" } } */
+/* { dg-final { scan-tree-dump-times "vectorized 2 loops" 1 "vect" } } */
diff --git a/gcc/tree-vect-loop.c b/gcc/tree-vect-loop.c
index c31bfbd..b89c09b 100644
--- a/gcc/tree-vect-loop.c
+++ b/gcc/tree-vect-loop.c
@@ -2615,7 +2615,7 @@ vect_is_simple_reduction_1 (loop_vec_info loop_info, gimple phi,
}
else if (INTEGRAL_TYPE_P (type) && check_reduction)
{
- if (TYPE_OVERFLOW_TRAPS (type))
+ if (!operation_no_trapping_overflow (type, code))
{
/* Changing the order of operations changes the semantics. */
if (dump_enabled_p ())
@@ -2624,7 +2624,8 @@ vect_is_simple_reduction_1 (loop_vec_info loop_info, gimple phi,
" (overflow traps): ");
return NULL;
}
- if (need_wrapping_integral_overflow && !TYPE_OVERFLOW_WRAPS (type))
+ if (need_wrapping_integral_overflow
+ && !operation_no_overflow_or_wraps (type, code))
{
/* Changing the order of operations changes the semantics. */
if (dump_enabled_p ())
diff --git a/gcc/tree.c b/gcc/tree.c
index 94263af..08fba14 100644
--- a/gcc/tree.c
+++ b/gcc/tree.c
@@ -7597,6 +7597,133 @@ commutative_ternary_tree_code (enum tree_code code)
return false;
}
+/* Returns true if CODE operating on operands of type TYPE can overflow. */
+
+bool
+operation_overflows (tree type, enum tree_code code)
+{
+ gcc_checking_assert (ANY_INTEGRAL_TYPE_P (type));
+
+ switch (code)
+ {
+ case PLUS_EXPR:
+ case MINUS_EXPR:
+ case MULT_EXPR:
+ case LSHIFT_EXPR:
+ /* Can overflow in various ways. */
+ return true;
+ case TRUNC_DIV_EXPR:
+ case EXACT_DIV_EXPR:
+ case FLOOR_DIV_EXPR:
+ case CEIL_DIV_EXPR:
+ /* For INT_MIN / -1. */
+ return true;
+ case NEGATE_EXPR:
+ case ABS_EXPR:
+ /* For -INT_MIN. */
+ return true;
+ default:
+ /* These operators cannot overflow. */
+ return false;
+ }
+}
+
+/* Returns true if CODE operating on operands of type TYPE doesn't overflow, or
+ ftrapv doesn't generate trapping insns for CODE. */
+
+bool
+operation_no_trapping_overflow (tree type, enum tree_code code)
+{
+ gcc_checking_assert (ANY_INTEGRAL_TYPE_P (type));
+
+ /* We don't generate instructions that trap on overflow for complex or vector
+ types. */
+ if (!INTEGRAL_TYPE_P (type))
+ return true;
+
+ if (!TYPE_OVERFLOW_TRAPS (type))
+ return true;
+
+ switch (code)
+ {
+ case PLUS_EXPR:
+ case MINUS_EXPR:
+ case MULT_EXPR:
+ case NEGATE_EXPR:
+ case ABS_EXPR:
+ /* These operators can overflow, and -ftrapv generates trapping code for
+ these. */
+ return false;
+ case TRUNC_DIV_EXPR:
+ case EXACT_DIV_EXPR:
+ case FLOOR_DIV_EXPR:
+ case CEIL_DIV_EXPR:
+ case LSHIFT_EXPR:
+ /* These operators can overflow, but -ftrapv does not generate trapping
+ code for these. */
+ return true;
+ default:
+ /* These operators cannot overflow. */
+ return true;
+ }
+}
+
+/* Returns true if CODE operating on operands of type TYPE cannot overflow, or
+ wraps on overflow. */
+
+bool
+operation_no_overflow_or_wraps (tree type, enum tree_code code)
+{
+ gcc_checking_assert (ANY_INTEGRAL_TYPE_P (type));
+
+ /* We don't take advantage of integral type overflow behaviour for complex and
+ vector types. */
+ if (!INTEGRAL_TYPE_P (type))
+ return false;
+
+ if (TYPE_OVERFLOW_WRAPS (type))
+ return true;
+
+ return !operation_overflows (type, code);
+}
+
+/* Returns true if CODE operating on operands of type TYPE can overflow, and
+ overflow is undefined. */
+
+bool
+operation_undefined_overflow (tree type, enum tree_code code)
+{
+ gcc_checking_assert (ANY_INTEGRAL_TYPE_P (type));
+
+ /* We don't take advantage of integral type overflow behaviour for complex and
+ vector types. */
+ if (!INTEGRAL_TYPE_P (type))
+ return false;
+
+ if (!TYPE_OVERFLOW_UNDEFINED (type))
+ return false;
+
+ switch (code)
+ {
+ case LSHIFT_EXPR:
+ /* LSHIFT_EXPR can overflow, but we don't take advantage of that:
+ GCC manual, C Implementation-defined behavior, Integers implementation:
+ GCC does not use the latitude given in C99 and C11 only to treat
+ certain aspects of signed << as undefined, but this is subject to
+ change. */
+ return false;
+ case TRUNC_DIV_EXPR:
+ case EXACT_DIV_EXPR:
+ case FLOOR_DIV_EXPR:
+ case CEIL_DIV_EXPR:
+ /* These operators can overflow, but we don't take advantage of that.
+ FIXME: where has this been documented? */
+ return false;
+ default:
+ return operation_overflows (type, code);
+ }
+}
+
namespace inchash
{
diff --git a/gcc/tree.h b/gcc/tree.h
index 6df2217..76a004e 100644
--- a/gcc/tree.h
+++ b/gcc/tree.h
@@ -4369,6 +4369,10 @@ extern int type_num_arguments (const_tree);
extern bool associative_tree_code (enum tree_code);
extern bool commutative_tree_code (enum tree_code);
extern bool commutative_ternary_tree_code (enum tree_code);
+extern bool operation_overflows (tree, enum tree_code);
+extern bool operation_no_trapping_overflow (tree, enum tree_code);
+extern bool operation_no_overflow_or_wraps (tree, enum tree_code);
+extern bool operation_undefined_overflow (tree, enum tree_code);
extern tree upper_bound_in_type (tree, tree);
extern tree lower_bound_in_type (tree, tree);
extern int operand_equal_for_phi_arg_p (const_tree, const_tree);
--
1.9.1