[PR87815]Don't generate shift sequence for load replacement in DSE when the mode size is not compile-time constant

[PR87815]Don't generate shift sequence for load replacement in DSE when the mode size is not compile-time constant

[Renlin Li]

[-- Attachment #1: Type: text/plain, Size: 973 bytes --]

Hi all,

The patch adds a check if the gap is compile-time constant.

This happens when dse decides to replace the load with previous store value.
The problem is that, shift sequence could not accept compile-time non-constant
mode operand.

Another issue raised from this issue is the inefficient code-generation for
general data manipulation over mask/predicate register.
In sve, some general data processing instructions don't apply on predicate
registers directly. In the worst(this) case, memory load/store is generated to reload
the value into a general purpose register for further data processing.
We need to improve that.

aarch64 sve test Okay, Okay to commit?

Regards,
Renlin

gcc/ChangeLog:

2018-10-31  Renlin Li  <renlin.li@arm.com>

	PR target/87815
	* dse.c (get_stored_val): Add check for compile-time
	  constantness of gap.

gcc/testsuite/ChangeLog:

2018-10-31  Renlin Li  <renlin.li@arm.com>

	PR target/87815
	* gcc.target/aarch64/sve/pr87815.c: New.

[-- Attachment #2: sve-patch.patch --]
[-- Type: text/x-patch, Size: 1019 bytes --]

diff --git a/gcc/dse.c b/gcc/dse.c
index cfebfa0e110be56f17337dcb152984d782528889..21d166d92fcc2c2a4dd6d04bb7a7247b79b81a62 100644
--- a/gcc/dse.c
+++ b/gcc/dse.c
@@ -1841,7 +1841,7 @@ get_stored_val (store_info *store_info, machine_mode read_mode,
   else
     gap = read_offset - store_info->offset;
 
-  if (maybe_ne (gap, 0))
+  if (gap.is_constant () && maybe_ne (gap, 0))
     {
       poly_int64 shift = gap * BITS_PER_UNIT;
       poly_int64 access_size = GET_MODE_SIZE (read_mode) + gap;
diff --git a/gcc/testsuite/gcc.target/aarch64/sve/pr87815.c b/gcc/testsuite/gcc.target/aarch64/sve/pr87815.c
new file mode 100644
index 0000000000000000000000000000000000000000..628cedb2acce82a86b61944eb6184d7fdbb2d656
--- /dev/null
+++ b/gcc/testsuite/gcc.target/aarch64/sve/pr87815.c
@@ -0,0 +1,13 @@
+/* { dg-do compile { target aarch64_asm_sve_ok } } */
+/* { dg-options "-O3" } */
+int a, b, d;
+short e;
+
+void f ()
+{
+  for (int i = 0; i < 8; i++)
+    {
+      e = b >= 2 ?: a >> b;
+      d = e && b;
+    }
+}

Re: [PR87815]Don't generate shift sequence for load replacement in DSE when the mode size is not compile-time constant

[Jeff Law]

On 10/31/18 5:13 AM, Renlin Li wrote:
> Hi all,
> 
> The patch adds a check if the gap is compile-time constant.
> 
> This happens when dse decides to replace the load with previous store
> value.
> The problem is that, shift sequence could not accept compile-time
> non-constant
> mode operand.
> 
> Another issue raised from this issue is the inefficient code-generation for
> general data manipulation over mask/predicate register.
> In sve, some general data processing instructions don't apply on predicate
> registers directly. In the worst(this) case, memory load/store is
> generated to reload
> the value into a general purpose register for further data processing.
> We need to improve that.
> 
> aarch64 sve test Okay, Okay to commit?
> 
> Regards,
> Renlin
> 
> gcc/ChangeLog:
> 
> 2018-10-31  Renlin Li  <renlin.li@arm.com>
> 
>     PR target/87815
>     * dse.c (get_stored_val): Add check for compile-time
>       constantness of gap.
> 
> gcc/testsuite/ChangeLog:
> 
> 2018-10-31  Renlin Li  <renlin.li@arm.com>
> 
>     PR target/87815
>     * gcc.target/aarch64/sve/pr87815.c: New.
OK
jeff