Re: [PATCH] haifa-sched: fix autopref_rank_for_schedule comparator [PR109187]

[Richard Biener via Gcc-patches]

On Tue, Mar 28, 2023 at 3:11 PM Alexander Monakov via Gcc-patches
 wrote:
>
> Do not attempt to use a plain subtraction for generating a three-way
> comparison result in autopref_rank_for_schedule qsort comparator, as
> offsets are not restricted and subtraction may overflow.  Open-code
> a safe three-way comparison instead.

OK.

> gcc/ChangeLog:
>
> PR rtl-optimization/109187
> * haifa-sched.cc (autopref_rank_for_schedule): Avoid use of 
> overflowing
> subtraction in three-way comparison.
>
> gcc/testsuite/ChangeLog:
>
> PR rtl-optimization/109187
> * gcc.dg/pr109187.c: New test.
> ---
>
> I think I can commit this as obvious if no comment in a day, but explicit ack
> is always appreciated.
>
> Alexander
>
>  gcc/haifa-sched.cc  | 2 +-
>  gcc/testsuite/gcc.dg/pr109187.c | 8 
>  2 files changed, 9 insertions(+), 1 deletion(-)
>  create mode 100644 gcc/testsuite/gcc.dg/pr109187.c
>
> diff --git a/gcc/haifa-sched.cc b/gcc/haifa-sched.cc
> index 4efaa9445..e11cc5c35 100644
> --- a/gcc/haifa-sched.cc
> +++ b/gcc/haifa-sched.cc
> @@ -5686,7 +5686,7 @@ autopref_rank_for_schedule (const rtx_insn *insn1, 
> const rtx_insn *insn2)
>
>if (!irrel1 && !irrel2)
> /* Sort memory references from lowest offset to the largest.  */
> -   r = data1->offset - data2->offset;
> +   r = (data1->offset > data2->offset) - (data1->offset < data2->offset);
>else if (write)
> /* Schedule "irrelevant" insns before memory stores to resolve
>as many producer dependencies of stores as possible.  */
> diff --git a/gcc/testsuite/gcc.dg/pr109187.c b/gcc/testsuite/gcc.dg/pr109187.c
> new file mode 100644
> index 0..1ef14a73d
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/pr109187.c
> @@ -0,0 +1,8 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O2 --param sched-autopref-queue-depth=1" } */
> +
> +void f(int *a)
> +{
> +  for (;;)
> +asm("" :: "r"(a[-0x1000]), "r"(a[0x1000]), "r"(a[0]) : "memory");
> +}
> --
> 2.39.1
>

[PATCH] haifa-sched: fix autopref_rank_for_schedule comparator [PR109187]

[Alexander Monakov via Gcc-patches]

Do not attempt to use a plain subtraction for generating a three-way
comparison result in autopref_rank_for_schedule qsort comparator, as
offsets are not restricted and subtraction may overflow.  Open-code
a safe three-way comparison instead.

gcc/ChangeLog:

PR rtl-optimization/109187
* haifa-sched.cc (autopref_rank_for_schedule): Avoid use of overflowing
subtraction in three-way comparison.

gcc/testsuite/ChangeLog:

PR rtl-optimization/109187
* gcc.dg/pr109187.c: New test.
---

I think I can commit this as obvious if no comment in a day, but explicit ack
is always appreciated.

Alexander

 gcc/haifa-sched.cc  | 2 +-
 gcc/testsuite/gcc.dg/pr109187.c | 8 
 2 files changed, 9 insertions(+), 1 deletion(-)
 create mode 100644 gcc/testsuite/gcc.dg/pr109187.c

diff --git a/gcc/haifa-sched.cc b/gcc/haifa-sched.cc
index 4efaa9445..e11cc5c35 100644
--- a/gcc/haifa-sched.cc
+++ b/gcc/haifa-sched.cc
@@ -5686,7 +5686,7 @@ autopref_rank_for_schedule (const rtx_insn *insn1, const 
rtx_insn *insn2)
 
   if (!irrel1 && !irrel2)
/* Sort memory references from lowest offset to the largest.  */
-   r = data1->offset - data2->offset;
+   r = (data1->offset > data2->offset) - (data1->offset < data2->offset);
   else if (write)
/* Schedule "irrelevant" insns before memory stores to resolve
   as many producer dependencies of stores as possible.  */
diff --git a/gcc/testsuite/gcc.dg/pr109187.c b/gcc/testsuite/gcc.dg/pr109187.c
new file mode 100644
index 0..1ef14a73d
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr109187.c
@@ -0,0 +1,8 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 --param sched-autopref-queue-depth=1" } */
+
+void f(int *a)
+{
+  for (;;)
+asm("" :: "r"(a[-0x1000]), "r"(a[0x1000]), "r"(a[0]) : "memory");
+}
-- 
2.39.1