[PATCH] simplify-rtx: Fix compare of comparisons (PR60818)

[PATCH] simplify-rtx: Fix compare of comparisons (PR60818)

[Segher Boessenkool]

The function simplify_binary_operation_1 has code that does
/* Convert (compare (gt (flags) 0) (lt (flags) 0)) to (flags).  */
but this transformation is only valid if "flags" has the same machine
mode as the outer compare.  This fixes it.

Bootstrapped and tested on powerpc64-linux {-m32,-m64} (and tested the
new testcase with {-m32,-m64}{,-misel}).  Is this okay for trunk?


Segher


2017-03-31  Segher Boessenkool  <segher@kernel.crashing.org>

	PR rtl-optimization/60818
	* simplify-rtx.c (simplify_binary_operation_1): Do not replace
	a compare of comparisons with the thing compared if this results
	in a different machine mode.

gcc/testsuite/
	PR rtl-optimization/60818
	* gcc.c-torture/compile/pr60818.c: New testcase.

---
 gcc/simplify-rtx.c                            | 6 +++---
 gcc/testsuite/gcc.c-torture/compile/pr60818.c | 5 +++++
 2 files changed, 8 insertions(+), 3 deletions(-)
 create mode 100644 gcc/testsuite/gcc.c-torture/compile/pr60818.c

diff --git a/gcc/simplify-rtx.c b/gcc/simplify-rtx.c
index 3022779..10c2800 100644
--- a/gcc/simplify-rtx.c
+++ b/gcc/simplify-rtx.c
@@ -2367,10 +2367,10 @@
 	      return xop00;
 
 	    if (REG_P (xop00) && REG_P (xop10)
-		&& GET_MODE (xop00) == GET_MODE (xop10)
 		&& REGNO (xop00) == REGNO (xop10)
-		&& GET_MODE_CLASS (GET_MODE (xop00)) == MODE_CC
-		&& GET_MODE_CLASS (GET_MODE (xop10)) == MODE_CC)
+		&& GET_MODE (xop00) == mode
+		&& GET_MODE (xop10) == mode
+		&& GET_MODE_CLASS (mode) == MODE_CC)
 	      return xop00;
 	}
       break;
diff --git a/gcc/testsuite/gcc.c-torture/compile/pr60818.c b/gcc/testsuite/gcc.c-torture/compile/pr60818.c
new file mode 100644
index 0000000..b6171bb
--- /dev/null
+++ b/gcc/testsuite/gcc.c-torture/compile/pr60818.c
@@ -0,0 +1,5 @@
+int
+lx (int oi, int mb)
+{
+  return (oi < mb) < (mb < oi);
+}
-- 
1.9.3

Re: [PATCH] simplify-rtx: Fix compare of comparisons (PR60818)

[Jeff Law]

On 03/31/2017 03:40 PM, Segher Boessenkool wrote:
> The function simplify_binary_operation_1 has code that does
> /* Convert (compare (gt (flags) 0) (lt (flags) 0)) to (flags).  */
> but this transformation is only valid if "flags" has the same machine
> mode as the outer compare.  This fixes it.
>
> Bootstrapped and tested on powerpc64-linux {-m32,-m64} (and tested the
> new testcase with {-m32,-m64}{,-misel}).  Is this okay for trunk?
>
>
> Segher
>
>
> 2017-03-31  Segher Boessenkool  <segher@kernel.crashing.org>
>
> 	PR rtl-optimization/60818
> 	* simplify-rtx.c (simplify_binary_operation_1): Do not replace
> 	a compare of comparisons with the thing compared if this results
> 	in a different machine mode.
>
> gcc/testsuite/
> 	PR rtl-optimization/60818
> 	* gcc.c-torture/compile/pr60818.c: New testcase.
Doesn't seem like a regression.  But I can't see how it could possibly 
result in any correctness issues -- the absolute worst would be a 
performance issue and even that seems highly unlikely.

OK for the trunk if you think it's worth fixing for gcc-7.  Else it's 
pre-approved for gcc-8.


jeff

Re: [PATCH] simplify-rtx: Fix compare of comparisons (PR60818)

[Segher Boessenkool]

On Mon, Apr 03, 2017 at 11:01:23AM -0600, Jeff Law wrote:
> >	PR rtl-optimization/60818
> >	* simplify-rtx.c (simplify_binary_operation_1): Do not replace
> >	a compare of comparisons with the thing compared if this results
> >	in a different machine mode.
> >
> >gcc/testsuite/
> >	PR rtl-optimization/60818
> >	* gcc.c-torture/compile/pr60818.c: New testcase.
> Doesn't seem like a regression.  But I can't see how it could possibly 
> result in any correctness issues -- the absolute worst would be a 
> performance issue and even that seems highly unlikely.

It ICEs with trunk, it didn't ICE with 6.

The problem is that changing the mode of the CC in the producer, while
not changing the mode in the consumer, is very wrong, and runs into
asserts later on.

> OK for the trunk if you think it's worth fixing for gcc-7.  Else it's 
> pre-approved for gcc-8.

I'll commit it then.  Thanks,


Segher

Re: [PATCH] simplify-rtx: Fix compare of comparisons (PR60818)

[Segher Boessenkool]

Hi!

Is this okay for backport to 5 and 6?


Segher


On Fri, Mar 31, 2017 at 09:40:34PM +0000, Segher Boessenkool wrote:
> The function simplify_binary_operation_1 has code that does
> /* Convert (compare (gt (flags) 0) (lt (flags) 0)) to (flags).  */
> but this transformation is only valid if "flags" has the same machine
> mode as the outer compare.  This fixes it.
> 
> Bootstrapped and tested on powerpc64-linux {-m32,-m64} (and tested the
> new testcase with {-m32,-m64}{,-misel}).  Is this okay for trunk?
> 
> 
> Segher
> 
> 
> 2017-03-31  Segher Boessenkool  <segher@kernel.crashing.org>
> 
> 	PR rtl-optimization/60818
> 	* simplify-rtx.c (simplify_binary_operation_1): Do not replace
> 	a compare of comparisons with the thing compared if this results
> 	in a different machine mode.
> 
> gcc/testsuite/
> 	PR rtl-optimization/60818
> 	* gcc.c-torture/compile/pr60818.c: New testcase.
> 
> ---
>  gcc/simplify-rtx.c                            | 6 +++---
>  gcc/testsuite/gcc.c-torture/compile/pr60818.c | 5 +++++
>  2 files changed, 8 insertions(+), 3 deletions(-)
>  create mode 100644 gcc/testsuite/gcc.c-torture/compile/pr60818.c
> 
> diff --git a/gcc/simplify-rtx.c b/gcc/simplify-rtx.c
> index 3022779..10c2800 100644
> --- a/gcc/simplify-rtx.c
> +++ b/gcc/simplify-rtx.c
> @@ -2367,10 +2367,10 @@
>  	      return xop00;
>  
>  	    if (REG_P (xop00) && REG_P (xop10)
> -		&& GET_MODE (xop00) == GET_MODE (xop10)
>  		&& REGNO (xop00) == REGNO (xop10)
> -		&& GET_MODE_CLASS (GET_MODE (xop00)) == MODE_CC
> -		&& GET_MODE_CLASS (GET_MODE (xop10)) == MODE_CC)
> +		&& GET_MODE (xop00) == mode
> +		&& GET_MODE (xop10) == mode
> +		&& GET_MODE_CLASS (mode) == MODE_CC)
>  	      return xop00;
>  	}
>        break;
> diff --git a/gcc/testsuite/gcc.c-torture/compile/pr60818.c b/gcc/testsuite/gcc.c-torture/compile/pr60818.c
> new file mode 100644
> index 0000000..b6171bb
> --- /dev/null
> +++ b/gcc/testsuite/gcc.c-torture/compile/pr60818.c
> @@ -0,0 +1,5 @@
> +int
> +lx (int oi, int mb)
> +{
> +  return (oi < mb) < (mb < oi);
> +}
> -- 
> 1.9.3