Re: [PATCH][PR tree-optimization/79578] Use operand_equal_p rather than pointer equality for base test

[Richard Biener]

On Thu, Feb 23, 2017 at 10:06 PM, Jeff Law  wrote:
> On 02/23/2017 02:02 AM, Richard Biener wrote:
>
>>> diff --git a/gcc/tree-ssa-dse.c b/gcc/tree-ssa-dse.c
>>> index 84c0b11..a82e164 100644
>>> --- a/gcc/tree-ssa-dse.c
>>> +++ b/gcc/tree-ssa-dse.c
>>> @@ -176,7 +176,7 @@ clear_bytes_written_by (sbitmap live_bytes, gimple
>>> *stmt, ao_ref *ref)
>>>/* Verify we have the same base memory address, the write
>>>   has a known size and overlaps with REF.  */
>>>if (valid_ao_ref_for_dse ()
>>> -  && write.base == ref->base
>>> +  && operand_equal_p (write.base, ref->base, 0)
>>
>>
>> As you've identified size and offset match you are really interested
>> in comparing the base addresses and thus should use OEP_ADDRESS_OF.
>
> I pondered that, but (perhaps incorrectly) thought that OEP_ADDRESS_OF was
> an optimization and that a more simple o_e_p with no flags was safer.
>
> I'm happy to change it, particularly if it's a correctness issue (in which
> case I think we've designed a horrible API for o_e_p, but such is life).  In
> fact, I've already bootstrapped and regression tested that change.

It's indeed an optimization to use OEP_ADDRESS_OF and 0 is more conservative.

Richard.

> jeff
>

Re: [PATCH][PR tree-optimization/79578] Use operand_equal_p rather than pointer equality for base test

[Jeff Law]

On 02/23/2017 02:02 AM, Richard Biener wrote:


diff --git a/gcc/tree-ssa-dse.c b/gcc/tree-ssa-dse.c
index 84c0b11..a82e164 100644
--- a/gcc/tree-ssa-dse.c
+++ b/gcc/tree-ssa-dse.c
@@ -176,7 +176,7 @@ clear_bytes_written_by (sbitmap live_bytes, gimple
*stmt, ao_ref *ref)
   /* Verify we have the same base memory address, the write
  has a known size and overlaps with REF.  */
   if (valid_ao_ref_for_dse ()
-  && write.base == ref->base
+  && operand_equal_p (write.base, ref->base, 0)


As you've identified size and offset match you are really interested
in comparing the base addresses and thus should use OEP_ADDRESS_OF.
I pondered that, but (perhaps incorrectly) thought that OEP_ADDRESS_OF 
was an optimization and that a more simple o_e_p with no flags was safer.


I'm happy to change it, particularly if it's a correctness issue (in 
which case I think we've designed a horrible API for o_e_p, but such is 
life).  In fact, I've already bootstrapped and regression tested that 
change.


jeff

Re: [PATCH][PR tree-optimization/79578] Use operand_equal_p rather than pointer equality for base test

[Richard Biener]

On Thu, Feb 23, 2017 at 6:49 AM, Jeff Law  wrote:
>
> tree-ssa-dse.c needs to verify when two writes have the same base address.
> Right now it uses pointer equality.  The testcase in BZ79578 shows that we
> should have been using operand_equal_p.
>
> This one-liner fixes that oversight.  Bootstrapped and regression tested on
> x86_64-linux-gnu.  Installed on the trunk.
>
> Jeff
>
> commit ef506ec9114a7fe27d9ee892c17edd100f72a963
> Author: law 
> Date:   Thu Feb 23 05:47:43 2017 +
>
> PR tree-optimization/79578
> * tree-ssa-dse.c (clear_bytes_written_by): Use operand_equal_p
> to compare base operands.
>
> PR tree-optimization/79578
> * g++.dg/tree-ssa/ssa-dse-3.C: New test.
>
> git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@245675
> 138bc75d-0d04-0410-961f-82ee72b054a4
>
> diff --git a/gcc/ChangeLog b/gcc/ChangeLog
> index 7155850..6da1d74 100644
> --- a/gcc/ChangeLog
> +++ b/gcc/ChangeLog
> @@ -1,3 +1,9 @@
> +2017-02-22 Jeff Law  
> +
> +   PR tree-optimization/79578
> +   * tree-ssa-dse.c (clear_bytes_written_by): Use operand_equal_p
> +   to compare base operands.
> +
>  2017-02-22  Segher Boessenkool  
>
> PR target/79211
> diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
> index ea5e251..d900cc3 100644
> --- a/gcc/testsuite/ChangeLog
> +++ b/gcc/testsuite/ChangeLog
> @@ -1,3 +1,8 @@
> +2017-02-22  Jeff Law  
> +
> +   PR tree-optimization/79578
> +   * g++.dg/tree-ssa/ssa-dse-3.C: New test.
> +
>  2017-02-22  Sameera Deshpande  
>
> * gcc.target/mips/msa-fp-cc.c: New test.
> diff --git a/gcc/testsuite/g++.dg/tree-ssa/ssa-dse-3.C
> b/gcc/testsuite/g++.dg/tree-ssa/ssa-dse-3.C
> new file mode 100644
> index 000..fe8f309
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/tree-ssa/ssa-dse-3.C
> @@ -0,0 +1,28 @@
> +/* { dg-do compile } */
> +/* { dg-options "-std=c++14 -O3 -fdump-tree-dse1-details" } */
> +
> +#include 
> +#include 
> +
> +struct A
> +{
> +std::uint16_t a, b;
> +};
> +
> +A* f(char* b) __attribute__((noinline));
> +
> +A* f(char* b) {
> +auto a = new(b) A{};
> +a->a = 1;
> +a->b = 2;
> +return a;
> +}
> +
> +int main() {
> +char b[sizeof(A)] alignas(A);
> +f(b);
> +}
> +
> +
> +/* { dg-final { scan-tree-dump "Deleted dead store: " "dse1" } } */
> +
> diff --git a/gcc/tree-ssa-dse.c b/gcc/tree-ssa-dse.c
> index 84c0b11..a82e164 100644
> --- a/gcc/tree-ssa-dse.c
> +++ b/gcc/tree-ssa-dse.c
> @@ -176,7 +176,7 @@ clear_bytes_written_by (sbitmap live_bytes, gimple
> *stmt, ao_ref *ref)
>/* Verify we have the same base memory address, the write
>   has a known size and overlaps with REF.  */
>if (valid_ao_ref_for_dse ()
> -  && write.base == ref->base
> +  && operand_equal_p (write.base, ref->base, 0)

As you've identified size and offset match you are really interested
in comparing the base addresses and thus should use OEP_ADDRESS_OF.

Richard.

>&& write.size == write.max_size
>&& ((write.offset < ref->offset
>&& write.offset + write.size > ref->offset)
>

[PATCH][PR tree-optimization/79578] Use operand_equal_p rather than pointer equality for base test

[Jeff Law]

tree-ssa-dse.c needs to verify when two writes have the same base 
address.  Right now it uses pointer equality.  The testcase in BZ79578 
shows that we should have been using operand_equal_p.


This one-liner fixes that oversight.  Bootstrapped and regression tested 
on x86_64-linux-gnu.  Installed on the trunk.


Jeff
commit ef506ec9114a7fe27d9ee892c17edd100f72a963
Author: law 
Date:   Thu Feb 23 05:47:43 2017 +

PR tree-optimization/79578
* tree-ssa-dse.c (clear_bytes_written_by): Use operand_equal_p
to compare base operands.

PR tree-optimization/79578
* g++.dg/tree-ssa/ssa-dse-3.C: New test.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@245675 
138bc75d-0d04-0410-961f-82ee72b054a4

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 7155850..6da1d74 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,9 @@
+2017-02-22 Jeff Law  
+
+   PR tree-optimization/79578
+   * tree-ssa-dse.c (clear_bytes_written_by): Use operand_equal_p
+   to compare base operands.
+
 2017-02-22  Segher Boessenkool  
 
PR target/79211
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index ea5e251..d900cc3 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,8 @@
+2017-02-22  Jeff Law  
+
+   PR tree-optimization/79578
+   * g++.dg/tree-ssa/ssa-dse-3.C: New test.
+
 2017-02-22  Sameera Deshpande  
 
* gcc.target/mips/msa-fp-cc.c: New test.
diff --git a/gcc/testsuite/g++.dg/tree-ssa/ssa-dse-3.C 
b/gcc/testsuite/g++.dg/tree-ssa/ssa-dse-3.C
new file mode 100644
index 000..fe8f309
--- /dev/null
+++ b/gcc/testsuite/g++.dg/tree-ssa/ssa-dse-3.C
@@ -0,0 +1,28 @@
+/* { dg-do compile } */
+/* { dg-options "-std=c++14 -O3 -fdump-tree-dse1-details" } */
+
+#include 
+#include 
+
+struct A
+{
+std::uint16_t a, b;
+};
+
+A* f(char* b) __attribute__((noinline));
+
+A* f(char* b) {
+auto a = new(b) A{};
+a->a = 1;
+a->b = 2;
+return a;
+}
+
+int main() {
+char b[sizeof(A)] alignas(A);
+f(b);
+}
+
+
+/* { dg-final { scan-tree-dump "Deleted dead store: " "dse1" } } */
+
diff --git a/gcc/tree-ssa-dse.c b/gcc/tree-ssa-dse.c
index 84c0b11..a82e164 100644
--- a/gcc/tree-ssa-dse.c
+++ b/gcc/tree-ssa-dse.c
@@ -176,7 +176,7 @@ clear_bytes_written_by (sbitmap live_bytes, gimple *stmt, 
ao_ref *ref)
   /* Verify we have the same base memory address, the write
  has a known size and overlaps with REF.  */
   if (valid_ao_ref_for_dse ()
-  && write.base == ref->base
+  && operand_equal_p (write.base, ref->base, 0)
   && write.size == write.max_size
   && ((write.offset < ref->offset
   && write.offset + write.size > ref->offset)