[Bug tree-optimization/96702] Failure to optimize comparisons involving result of subtraction
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96702
--- Comment #5 from Andrew Pinski ---
(In reply to Andrew Pinski from comment #4)
> The pattern:
> /* X - Y < X is the same as Y > 0 when there is no overflow.
>For equality, this is also true with wrapping overflow. */
> (for op (simple_comparison)
> (simplify
> (op:c @0 (minus@2 @0 @1))
> (if (ANY_INTEGRAL_TYPE_P (TREE_TYPE (@0))
>&& (TYPE_OVERFLOW_UNDEFINED (TREE_TYPE (@0))
> || ((op == EQ_EXPR || op == NE_EXPR)
> && TYPE_OVERFLOW_WRAPS (TREE_TYPE (@0
>&& (CONSTANT_CLASS_P (@1) || single_use (@2)))
>(op @1 { build_zero_cst (TREE_TYPE (@1)); }
>
> https://gcc.gnu.org/pipermail/gcc-patches/2017-October/484606.html describes
> why there was a single use but I wonder if ranger now does not cause the
> need for the single_use
Looks like that issue was fixed in GCC 9 so maybe the 2 uses of single_use can
be removed ...
[Bug tree-optimization/96702] Failure to optimize comparisons involving result of subtraction
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96702
--- Comment #4 from Andrew Pinski ---
The pattern:
/* X - Y < X is the same as Y > 0 when there is no overflow.
For equality, this is also true with wrapping overflow. */
(for op (simple_comparison)
(simplify
(op:c @0 (minus@2 @0 @1))
(if (ANY_INTEGRAL_TYPE_P (TREE_TYPE (@0))
&& (TYPE_OVERFLOW_UNDEFINED (TREE_TYPE (@0))
|| ((op == EQ_EXPR || op == NE_EXPR)
&& TYPE_OVERFLOW_WRAPS (TREE_TYPE (@0
&& (CONSTANT_CLASS_P (@1) || single_use (@2)))
(op @1 { build_zero_cst (TREE_TYPE (@1)); }
https://gcc.gnu.org/pipermail/gcc-patches/2017-October/484606.html describes
why there was a single use but I wonder if ranger now does not cause the need
for the single_use
[Bug tree-optimization/96702] Failure to optimize comparisons involving result of subtraction
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96702 --- Comment #3 from Andrew Pinski --- wait that is for unsigned types and we don't have an unsigned type here ..
[Bug tree-optimization/96702] Failure to optimize comparisons involving result of subtraction
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96702 --- Comment #2 from Andrew Pinski --- The comment says: /* To detect overflow in unsigned A - B, A < B is simpler than A - B > A. However, the detection logic for SUB_OVERFLOW in tree-ssa-math-opts.cc expects the long form, so we restrict the transformation for now. */ (for cmp (gt le) (simplify (cmp:c (minus@2 @0 @1) @0) (if (single_use (@2) I am curious if that is still true ...
[Bug tree-optimization/96702] Failure to optimize comparisons involving result of subtraction
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96702 Andrew Pinski changed: What|Removed |Added Status|UNCONFIRMED |NEW Last reconfirmed||2021-08-17 Ever confirmed|0 |1 --- Comment #1 from Andrew Pinski --- Confirmed. The problem is c is used twice. we handle both optimizations just fine alone, just not when together. There might be either a :s that maybe should not be there in match.pd or an explict check for used more than once.
[Bug tree-optimization/96702] Failure to optimize comparisons involving result of subtraction
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96702 Andrew Pinski changed: What|Removed |Added Severity|normal |enhancement
