phiopt: Drop SSA_NAME_RANGE_INFO in maybe equal case [PR108166]

The following place in value_replacement is after proving that
x == cst1 ? cst2 : x
phi result is only used in a comparison with constant which doesn't
care if it compares cst1 or cst2 and replaces it with x.
The testcase is miscompiled because we have after the replacement
incorrect range info for the phi result, we would need to
effectively union the phi result range with cst1 (oarg in the code)
because previously that constant might be missing in the range, but
newly it can appear (we've just verified that the single use stmt
of the phi result doesn't care about that value in particular).

The following patch just resets the info, bootstrapped/regtested
on x86_64-linux and i686-linux, ok for trunk?

Aldy/Andrew, how would one instead union the SSA_NAME_RANGE_INFO
with some INTEGER_CST and store it back into SSA_NAME_RANGE_INFO
(including adjusting non-zero bits and the like)?

2022-12-22  Jakub Jelinek  <jakub@redhat.com>

	PR tree-optimization/108166
	* tree-ssa-phiopt.cc (value_replacement): For the maybe_equal_p
	case turned into equal_p reset SSA_NAME_RANGE_INFO of phi result.

	* g++.dg/torture/pr108166.C: New test.

(cherry picked from commit 5c17adfb5d08e34da7a7f234dfc2ed1f0aaadaa9)

diff --git a/gcc/testsuite/g++.dg/torture/pr108166.C b/gcc/testsuite/g++.dg/torture/pr108166.C
new file mode 100644 (file)
index 0000000..037fc27
--- /dev/null
+++ b/gcc/testsuite/g++.dg/torture/pr108166.C
@@ -0,0 +1,26 @@
+// PR tree-optimization/108166
+// { dg-do run }
+
+bool a, b;
+int d, c;
+
+const int &
+foo (const int &f, const int &g)
+{
+  return !f ? f : g;
+}
+
+__attribute__((noipa)) void
+bar (int)
+{
+}
+
+int
+main ()
+{
+  c = foo (b, 0) > ((b ? d : b) ?: 8);
+  a = b ? d : b;
+  bar (a);
+  if (a != 0)
+    __builtin_abort ();
+}

diff --git a/gcc/tree-ssa-phiopt.cc b/gcc/tree-ssa-phiopt.cc
index b8e57bb470ea63371fb842eb091bd26f774106c4..c56d0b9ff151725ce97a1ecca0476f034cb71a60 100644 (file)
--- a/gcc/tree-ssa-phiopt.cc
+++ b/gcc/tree-ssa-phiopt.cc
@@ -1454,6 +1454,12 @@ value_replacement (basic_block cond_bb, basic_block middle_bb,
                  default:
                    break;
                  }
+             if (equal_p)
+               /* After the optimization PHI result can have value
+                  which it couldn't have previously.
+                  We could instead of resetting it union the range
+                  info with oarg.  */
+               reset_flow_sensitive_info (gimple_phi_result (phi));
              if (equal_p && MAY_HAVE_DEBUG_BIND_STMTS)
                {
                  imm_use_iterator imm_iter;