Re: [PATCH] LoongArch: fix signed overflow in loongarch_emit_int_compare

[Xi Ruoyao via Gcc-patches]

On Sun, 2022-11-06 at 09:46 +0800, Lulu Cheng wrote:
> I think it should be here:
> 
>   if (!increment && !decrement)
>  continue;
> 
> + if ((increment && rhs == HOST_WIDE_INT_MAX)
> + || (decrement && rhs == HOST_WIDE_INT_MIN))
> +   break;
> +
> 
> It is not necessary to continue when *code matches one of 
> mag_comparisons[i].

Ah yes, I misread the code :(.

-- 
Xi Ruoyao 
School of Aerospace Science and Technology, Xidian University

Re: [PATCH] LoongArch: fix signed overflow in loongarch_emit_int_compare

[Lulu Cheng]

在 2022/11/4 下午2:39, Xi Ruoyao 写道:

Signed overflow is an undefined behavior, so we need to prevent it from
happening, instead of "checking" the result.

gcc/ChangeLog:

* config/loongarch/loongarch.cc (loongarch_emit_int_compare):
Avoid signed overflow.
---

Bootstrapped and regtested on loongarch64-linux-gnu.  OK for trunk?

  gcc/config/loongarch/loongarch.cc | 7 ---
  1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/gcc/config/loongarch/loongarch.cc 
b/gcc/config/loongarch/loongarch.cc
index f54c233f90c..032fb1474c7 100644
--- a/gcc/config/loongarch/loongarch.cc
+++ b/gcc/config/loongarch/loongarch.cc
@@ -4175,13 +4175,14 @@ loongarch_emit_int_compare (enum rtx_code *code, rtx 
*op0, rtx *op1)
  HOST_WIDE_INT new_rhs;
  bool increment = *code == mag_comparisons[i][0];
  bool decrement = *code == mag_comparisons[i][1];
- if (!increment && !decrement)
+ if ((!increment && !decrement)
+ || (increment && rhs == HOST_WIDE_INT_MAX)
+ || (decrement && rhs == HOST_WIDE_INT_MIN))
continue;


I think it should be here:

 if (!increment && !decrement)
    continue;

+ if ((increment && rhs == HOST_WIDE_INT_MAX)
+ || (decrement && rhs == HOST_WIDE_INT_MIN))
+   break;
+

It is not necessary to continue when *code matches one of 
mag_comparisons[i].


  
  	  new_rhs = rhs + (increment ? 1 : -1);

  if (loongarch_integer_cost (new_rhs)
-   < loongarch_integer_cost (rhs)
- && (rhs < 0) == (new_rhs < 0))
+   < loongarch_integer_cost (rhs))
{
  *op1 = GEN_INT (new_rhs);
  *code = mag_comparisons[i][increment];

[PATCH] LoongArch: fix signed overflow in loongarch_emit_int_compare

[Xi Ruoyao via Gcc-patches]

Signed overflow is an undefined behavior, so we need to prevent it from
happening, instead of "checking" the result.

gcc/ChangeLog:

* config/loongarch/loongarch.cc (loongarch_emit_int_compare):
Avoid signed overflow.
---

Bootstrapped and regtested on loongarch64-linux-gnu.  OK for trunk?

 gcc/config/loongarch/loongarch.cc | 7 ---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/gcc/config/loongarch/loongarch.cc 
b/gcc/config/loongarch/loongarch.cc
index f54c233f90c..032fb1474c7 100644
--- a/gcc/config/loongarch/loongarch.cc
+++ b/gcc/config/loongarch/loongarch.cc
@@ -4175,13 +4175,14 @@ loongarch_emit_int_compare (enum rtx_code *code, rtx 
*op0, rtx *op1)
  HOST_WIDE_INT new_rhs;
  bool increment = *code == mag_comparisons[i][0];
  bool decrement = *code == mag_comparisons[i][1];
- if (!increment && !decrement)
+ if ((!increment && !decrement)
+ || (increment && rhs == HOST_WIDE_INT_MAX)
+ || (decrement && rhs == HOST_WIDE_INT_MIN))
continue;
 
  new_rhs = rhs + (increment ? 1 : -1);
  if (loongarch_integer_cost (new_rhs)
-   < loongarch_integer_cost (rhs)
- && (rhs < 0) == (new_rhs < 0))
+   < loongarch_integer_cost (rhs))
{
  *op1 = GEN_INT (new_rhs);
  *code = mag_comparisons[i][increment];
-- 
2.38.1