Message ID | 20221006105110.1719060-1-aldyh@redhat.com |
---|---|
State | New |
Headers | show |
Series | [RFC] Add op1_range for __builtin_signbit. | expand |
I have committed this patch, as the __builtin_signbit range-op entry is correct. I'd still like clarification on the folding). Aldy On Thu, Oct 6, 2022 at 12:51 PM Aldy Hernandez <aldyh@redhat.com> wrote: > > This is the op1_range range-op entry for __builtin_signbit. It allows > us to wind back through a call to signbit. > > For example, on the true side of if (__builtin_signbit(x_5) != 0) we > can crop down the range of x_5 to: > > [frange] float [-Inf, -0.0 (-0x0.0p+0)] -NAN > > Similarly on the false side, we can crop to: > > [frange] float [0.0 (0x0.0p+0), +Inf] +NAN > > This brings about an interesting question, can we fold the second > conditional here as always false? > > void foo(float x) > { > if (__builtin_signbit (x)) > { > if (x > 0.0) > link_error(); > } > } > > The only values for x at the second conditional are negative values, > or -NAN, so it will always evaluate to false. ISTM that we > *shouldn't* fold this conditional as there is user observable behavior > if there is a signaling NAN. For that matter, that is exactly what we > do in ranger-ops. We leave the conditional in place, but ranger > is able to determine that "x" is UNDEFINED on the path leading up to > link_error: > > =========== BB 3 ============ > Imports: x_3(D) > Exports: x_3(D) > x_3(D) [frange] float [-Inf, -0.0 (-0x0.0p+0)] -NAN > <bb 3> : > if (x_3(D) > 0.0) > goto <bb 4>; [INV] > else > goto <bb 5>; [INV] > > 3->4 (T) x_3(D) : [frange] UNDEFINED > 3->5 (F) x_3(D) : [frange] float [-Inf, -0.0 (-0x0.0p+0)] -NAN > > This would allow users of ranger to query x_3 on the 3->4 and notice > it's unreachable, without VRP removing the conditional. > > I believe this is correct, but would like confirmation from the experts. > > gcc/ChangeLog: > > * gimple-range-op.cc: Add op1_range entry for __builtin_signbit. > > gcc/testsuite/ChangeLog: > > * gcc.dg/tree-ssa/vrp-float-signbit-3.c: New test. > --- > gcc/gimple-range-op.cc | 20 +++++++++++++++++++ > .../gcc.dg/tree-ssa/vrp-float-signbit-3.c | 14 +++++++++++++ > 2 files changed, 34 insertions(+) > create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/vrp-float-signbit-3.c > > diff --git a/gcc/gimple-range-op.cc b/gcc/gimple-range-op.cc > index 42ebc7d6ce5..abc33e7af0c 100644 > --- a/gcc/gimple-range-op.cc > +++ b/gcc/gimple-range-op.cc > @@ -306,6 +306,7 @@ class cfn_signbit : public range_operator_float > { > public: > using range_operator_float::fold_range; > + using range_operator_float::op1_range; > virtual bool fold_range (irange &r, tree type, const frange &lh, > const irange &, relation_kind) const > { > @@ -320,6 +321,25 @@ public: > } > return false; > } > + virtual bool op1_range (frange &r, tree type, const irange &lhs, > + const frange &, relation_kind) const override > + { > + if (lhs.zero_p ()) > + { > + r.set (type, dconst0, frange_val_max (type)); > + r.update_nan (false); > + return true; > + } > + if (!lhs.contains_p (build_zero_cst (lhs.type ()))) > + { > + REAL_VALUE_TYPE dconstm0 = dconst0; > + dconstm0.sign = 1; > + r.set (type, frange_val_min (type), dconstm0); > + r.update_nan (true); > + return true; > + } > + return false; > + } > } op_cfn_signbit; > > // Implement range operator for CFN_BUILT_IN_TOUPPER and CFN_BUILT_IN_TOLOWER. > diff --git a/gcc/testsuite/gcc.dg/tree-ssa/vrp-float-signbit-3.c b/gcc/testsuite/gcc.dg/tree-ssa/vrp-float-signbit-3.c > new file mode 100644 > index 00000000000..dd3090aeb10 > --- /dev/null > +++ b/gcc/testsuite/gcc.dg/tree-ssa/vrp-float-signbit-3.c > @@ -0,0 +1,14 @@ > +// { dg-do compile } > +// { dg-options "-O2 -ffast-math -fdump-tree-evrp" } > + > +void link_error(); > + > +void foo(float x) > +{ > + if (__builtin_signbit (x)) > + { > + if (x > 0.0) > + link_error(); > + } > +} > +// { dg-final { scan-tree-dump-not "link_error" "evrp" } } > -- > 2.37.1 >
diff --git a/gcc/gimple-range-op.cc b/gcc/gimple-range-op.cc index 42ebc7d6ce5..abc33e7af0c 100644 --- a/gcc/gimple-range-op.cc +++ b/gcc/gimple-range-op.cc @@ -306,6 +306,7 @@ class cfn_signbit : public range_operator_float { public: using range_operator_float::fold_range; + using range_operator_float::op1_range; virtual bool fold_range (irange &r, tree type, const frange &lh, const irange &, relation_kind) const { @@ -320,6 +321,25 @@ public: } return false; } + virtual bool op1_range (frange &r, tree type, const irange &lhs, + const frange &, relation_kind) const override + { + if (lhs.zero_p ()) + { + r.set (type, dconst0, frange_val_max (type)); + r.update_nan (false); + return true; + } + if (!lhs.contains_p (build_zero_cst (lhs.type ()))) + { + REAL_VALUE_TYPE dconstm0 = dconst0; + dconstm0.sign = 1; + r.set (type, frange_val_min (type), dconstm0); + r.update_nan (true); + return true; + } + return false; + } } op_cfn_signbit; // Implement range operator for CFN_BUILT_IN_TOUPPER and CFN_BUILT_IN_TOLOWER. diff --git a/gcc/testsuite/gcc.dg/tree-ssa/vrp-float-signbit-3.c b/gcc/testsuite/gcc.dg/tree-ssa/vrp-float-signbit-3.c new file mode 100644 index 00000000000..dd3090aeb10 --- /dev/null +++ b/gcc/testsuite/gcc.dg/tree-ssa/vrp-float-signbit-3.c @@ -0,0 +1,14 @@ +// { dg-do compile } +// { dg-options "-O2 -ffast-math -fdump-tree-evrp" } + +void link_error(); + +void foo(float x) +{ + if (__builtin_signbit (x)) + { + if (x > 0.0) + link_error(); + } +} +// { dg-final { scan-tree-dump-not "link_error" "evrp" } }