Re: [tree-optimization/71947] Avoid unwanted propagations

[Jeff Law]

On 10/12/2016 09:00 AM, Georg-Johann Lay wrote:

On 10.10.2016 23:06, Jeff Law 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).

Bootstrapped and regression tested on x86_64.  Applied to the trunk.

commit 6223e6e425b6de916f0330b9dbe5698765d4a73c
Author: law 
Date:   Mon Oct 10 20:40:59 2016 +

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  
+
+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  

 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  
+
+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  

 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 000..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 000..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 000..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 000..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));



Hi, shouldn't this test be restricted to target machines that understand
MOVQ?

Same 

Re: [tree-optimization/71947] Avoid unwanted propagations

[Jeff Law]

On 10/12/2016 08:36 AM, Christophe Lyon wrote:


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:

Most likely branch-costing is the culprit.  Let me see what I can do...

jeff

Re: [tree-optimization/71947] Avoid unwanted propagations

[Georg-Johann Lay]

On 10.10.2016 23:06, Jeff Law 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).

Bootstrapped and regression tested on x86_64.  Applied to the trunk.

commit 6223e6e425b6de916f0330b9dbe5698765d4a73c
Author: law 
Date:   Mon Oct 10 20:40:59 2016 +

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  
+
+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  

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  
+
+   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  

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 000..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 000..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 000..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 000..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));



Hi, shouldn't this test be restricted to target machines that understand MOVQ?

Same issue for 

Re: [tree-optimization/71947] Avoid unwanted propagations

[Christophe Lyon]

Hi Jeff,


On 10 October 2016 at 23:06, Jeff Law  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 
> Date:   Mon Oct 10 20:40:59 2016 +
>
> 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  
> +
> +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  
>
> 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  
> +
> +   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  
>
> 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 000..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 000..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 000..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
> 

[tree-optimization/71947] Avoid unwanted propagations

[Jeff Law]

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).


Bootstrapped and regression tested on x86_64.  Applied to the trunk.

commit 6223e6e425b6de916f0330b9dbe5698765d4a73c
Author: law 
Date:   Mon Oct 10 20:40:59 2016 +

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  
+
+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  
 
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  
+
+   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  
 
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 000..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 000..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 000..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 000..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)