tree-ssa-math-opts: Fix is_widening_mult_rhs_p - unbreak bootstrap [PR113705]

On Tue, Jan 30, 2024 at 07:33:10AM -0000, Roger Sayle wrote:
+             wide_int bits = wide_int::from (tree_nonzero_bits (rhs),
+                                             prec,
+                                             TYPE_SIGN (TREE_TYPE (rhs)));
...
> +               if (gimple_assign_rhs_code (stmt) == BIT_AND_EXPR
> +                   && TREE_CODE (gimple_assign_rhs2 (stmt)) == INTEGER_CST
> +                   && wi::to_wide (gimple_assign_rhs2 (stmt))
> +                      == wi::mask (hprec, false, prec))

This change broke bootstrap on aarch64-linux.
The problem can be seen even on the reduced testcase.

The IL on the unreduced testcase before widening_mul has:
  # val_583 = PHI <val_26(13), val_164(40)>
...
  pretmp_266 = MEM[(const struct wide_int_storage *)&D.160657].len;
  _264 = pretmp_266 & 65535;
...
  _176 = (sizetype) val_583;
  _439 = (sizetype) _264;
  _284 = _439 * 8;
  _115 = _176 + _284;
where 583/266/264 have unsigned int type and 176/439/284/115 have sizetype.
widening_mul first turns that into:
  # val_583 = PHI <val_26(13), val_164(40)>
...
  pretmp_266 = MEM[(const struct wide_int_storage *)&D.160657].len;
  _264 = pretmp_266 & 65535;
...
  _176 = (sizetype) val_583;
  _439 = (sizetype) _264;
  _284 = _264 w* 8;
  _115 = _176 + _284;
and then is_widening_mult_rhs_p is called, with type sizetype (64-bit),
rhs _264, hprec 32 and prec 64.  Now tree_nonzero_bits (rhs) is
65535, so bits is 64-bit wide_int 65535, stmt is BIT_AND_EXPR,
but we ICE on the
wi::to_wide (gimple_assign_rhs2 (stmt)) == wi::mask (hprec, false, prec)
comparison because wi::to_wide on gimple_assign_rhs2 (stmt) - unsigned int
65535 gives 32-bit wide_int 65535, while wi::mask (hprec, false, prec)
gives 64-bit wide_int 0xffffffff and comparison between different precision
wide_ints is forbidden.

The following patch fixes it the same way how bits is computed earlier,
by calling wide_int::from on the wi::to_wide (gimple_assign_rhs2 (stmt)),
so we compare 64-bit 65535 with 64-bit 0xffffffff.

2024-02-02  Jakub Jelinek  <jakub@redhat.com>

	PR middle-end/113705
	* tree-ssa-math-opts.cc (is_widening_mult_rhs_p): Use wide_int_from
	around wi::to_wide in order to compare value in prec precision.

	* g++.dg/opt/pr113705.C: New test.

diff --git a/gcc/testsuite/g++.dg/opt/pr113705.C b/gcc/testsuite/g++.dg/opt/pr113705.C
new file mode 100644 (file)
index 0000000..39fb047
--- /dev/null
+++ b/gcc/testsuite/g++.dg/opt/pr113705.C
@@ -0,0 +1,68 @@
+// PR middle-end/113705
+// { dg-do compile { target c++17 } }
+// { dg-options "-O2 -w" }
+
+void foo ();
+template <typename T> struct A : T { long bar () const; };
+int a;
+
+template <typename T>
+long
+A<T>::bar () const
+{
+  return this->baz ()[a];
+}
+
+struct B {
+  struct { long b[1]; long c; } u;
+  unsigned d;
+  int e;
+  B (const B &);
+  ~B ();
+  const long *baz () const;
+  unsigned qux () const;
+};
+
+B::B (const B &)
+{
+  if (__builtin_expect (e, 0))
+    u.c = 0;
+}
+
+B::~B ()
+{
+  if (__builtin_expect (e, 0))
+    foo ();
+}
+
+const long *
+B::baz () const
+{
+  return u.b;
+}
+
+unsigned
+B::qux () const
+{
+  return d;
+}
+
+struct C { A<B> corge () const; A<B> *f; };
+
+A<B>
+C::corge () const
+{
+  return f[1];
+}
+
+void
+test (C r, long *h, unsigned short *d)
+{
+  for (int j = 0; j < 8; ++j)
+    {
+      A g = r.corge ();
+      *d = g.qux ();
+      for (unsigned i = 0; i < *d; ++i)
+       *h++ = g.bar ();
+    }
+}

diff --git a/gcc/tree-ssa-math-opts.cc b/gcc/tree-ssa-math-opts.cc
index cffe7573f794731629335965eb2a0f45b4d47857..aa9f7b57999469c312285bb50c41ff90536cf4f3 100644 (file)
--- a/gcc/tree-ssa-math-opts.cc
+++ b/gcc/tree-ssa-math-opts.cc
@@ -2572,7 +2572,8 @@ is_widening_mult_rhs_p (tree type, tree rhs, tree *type_out,
              if (is_gimple_assign (stmt)
                  && gimple_assign_rhs_code (stmt) == BIT_AND_EXPR
                  && TREE_CODE (gimple_assign_rhs2 (stmt)) == INTEGER_CST
-                 && wi::to_wide (gimple_assign_rhs2 (stmt))
+                 && wide_int::from (wi::to_wide (gimple_assign_rhs2 (stmt)),
+                                    prec, TYPE_SIGN (TREE_TYPE (rhs)))
                     == wi::mask (hprec, false, prec))
                *new_rhs_out = gimple_assign_rhs1 (stmt);
              else