From 4c57e57b370333ae30feba624ab9caa69a33e15c Mon Sep 17 00:00:00 2001 From: Aldy Hernandez Date: Fri, 11 Nov 2022 18:46:01 +0100 Subject: [PATCH] [range-ops] Add ability to represent open intervals in frange. Currently we represent < and > with a closed interval. So < 3.0 is represented as [-INF, +3.0]. This means 3.0 is included in the range, and though not ideal, is conservatively correct. Jakub has found a couple cases where properly representing < and > would help optimizations and tests, and this patch allows representing open intervals with real_nextafter. There are a few caveats. First, we leave MODE_COMPOSITE_P types pessimistically as a closed interval. Second, for -ffinite-math-only, real_nextafter will saturate the maximum representable number into +INF. However, this will still do the right thing, as frange::set() will crop things appropriately. Finally, and most frustratingly, representing < and > -+0.0 is problematic because we flush denormals to zero. Let me explain... real_nextafter(+0.0, +INF) gives 0x0.8p-148 as expected, but setting a range to this value yields [+0.0, 0x0.8p-148] because of the flushing. On the other hand, real_nextafter(+0.0, -INF) (surprisingly) gives -0.0.8p-148, but setting a range to that value yields [-0.0x8p-148, -0.0]. I say surprising, because according to cppreference.com, std::nextafter(+0.0, -INF) should give -0.0. But that's neither here nor there because our flushing denormals to zero prevents us from even representing ranges involving small values around 0.0. We ultimately end up with ranges looking like this: > +0.0 => [+0.0, INF] > -0.0 => [+0.0, INF] < +0.0 => [-INF, -0.0] < -0.0 => [-INF, -0.0] I suppose this is no worse off that what we had before with closed intervals. One could even argue that we're better because we at least have the right sign now ;-). gcc/ChangeLog: * range-op-float.cc (build_lt): Adjust with frange_nextafter instead of default to a closed range. (build_gt): Same. --- gcc/range-op-float.cc | 23 +++++++++++++++++++---- 1 file changed, 19 insertions(+), 4 deletions(-) diff --git a/gcc/range-op-float.cc b/gcc/range-op-float.cc index 4472337e03ef..53a0928c6aa9 100644 --- a/gcc/range-op-float.cc +++ b/gcc/range-op-float.cc @@ -381,9 +381,17 @@ build_lt (frange &r, tree type, const frange &val) r.set_undefined (); return false; } - // We only support closed intervals. + REAL_VALUE_TYPE ninf = frange_val_min (type); - r.set (type, ninf, val.upper_bound ()); + REAL_VALUE_TYPE prev = val.upper_bound (); + machine_mode mode = TYPE_MODE (type); + // Default to the conservatively correct closed ranges for + // MODE_COMPOSITE_P, otherwise use nextafter. Note that for + // !HONOR_INFINITIES, nextafter will yield -INF, but frange::set() + // will crop the range appropriately. + if (!MODE_COMPOSITE_P (mode)) + frange_nextafter (mode, prev, ninf); + r.set (type, ninf, prev); return true; } @@ -424,9 +432,16 @@ build_gt (frange &r, tree type, const frange &val) return false; } - // We only support closed intervals. REAL_VALUE_TYPE inf = frange_val_max (type); - r.set (type, val.lower_bound (), inf); + REAL_VALUE_TYPE next = val.lower_bound (); + machine_mode mode = TYPE_MODE (type); + // Default to the conservatively correct closed ranges for + // MODE_COMPOSITE_P, otherwise use nextafter. Note that for + // !HONOR_INFINITIES, nextafter will yield +INF, but frange::set() + // will crop the range appropriately. + if (!MODE_COMPOSITE_P (mode)) + frange_nextafter (mode, next, inf); + r.set (type, next, inf); return true; } -- 2.47.2