[gcc r12-3916] Return VARYING in range_on_path_entry if nothing found.

[gcc r12-3916] Return VARYING in range_on_path_entry if nothing found.

[Aldy Hernandez]

https://gcc.gnu.org/g:fb8b72ebb5b0bf40f7dfef9154c42320ce46f2a7

commit r12-3916-gfb8b72ebb5b0bf40f7dfef9154c42320ce46f2a7
Author: Aldy Hernandez <aldyh@redhat.com>
Date:   Tue Sep 28 09:38:50 2021 +0200

    Return VARYING in range_on_path_entry if nothing found.
    
    The problem here is that the solver's code solving unknown SSAs on entry
    to a path was returning UNDEFINED if there were no incoming edges to the
    start of the path that were not the function entry block.  This caused a
    cascade of pain down stream.
    
    Tested on x86-64 Linux.
    
            PR tree-optimization/102511
    
    gcc/ChangeLog:
    
            * gimple-range-path.cc (path_range_query::range_on_path_entry):
            Return VARYING when nothing found.
    
    gcc/testsuite/ChangeLog:
    
            * gcc.dg/pr102511.c: New test.
            * gcc.dg/tree-ssa/ssa-dom-thread-14.c: Adjust.

Diff:
---
 gcc/gimple-range-path.cc                          | 11 ++++++++++-
 gcc/testsuite/gcc.dg/pr102511.c                   | 21 +++++++++++++++++++++
 gcc/testsuite/gcc.dg/tree-ssa/ssa-dom-thread-14.c |  2 +-
 3 files changed, 32 insertions(+), 2 deletions(-)

diff --git a/gcc/gimple-range-path.cc b/gcc/gimple-range-path.cc
index 71e04e4deba..9da67d2a35b 100644
--- a/gcc/gimple-range-path.cc
+++ b/gcc/gimple-range-path.cc
@@ -136,14 +136,23 @@ path_range_query::range_on_path_entry (irange &r, tree name)
 {
   int_range_max tmp;
   basic_block entry = entry_bb ();
+  bool changed = false;
+
   r.set_undefined ();
   for (unsigned i = 0; i < EDGE_COUNT (entry->preds); ++i)
     {
       edge e = EDGE_PRED (entry, i);
       if (e->src != ENTRY_BLOCK_PTR_FOR_FN (cfun)
 	  && m_ranger.range_on_edge (tmp, e, name))
-	r.union_ (tmp);
+	{
+	  r.union_ (tmp);
+	  changed = true;
+	}
     }
+
+  // Make sure we don't return UNDEFINED by mistake.
+  if (!changed)
+    r.set_varying (TREE_TYPE (name));
 }
 
 // Return the range of NAME at the end of the path being analyzed.
diff --git a/gcc/testsuite/gcc.dg/pr102511.c b/gcc/testsuite/gcc.dg/pr102511.c
new file mode 100644
index 00000000000..8a9af347305
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr102511.c
@@ -0,0 +1,21 @@
+// { dg-do run }
+// { dg-options "-O3" }
+
+char arr_15 [8];
+__attribute__((noipa))
+void test(signed char a, unsigned short b, unsigned long long c,
+          unsigned short f) {
+  for (int d = b - 8; d < b; d += 2)
+    for (short e = 0; e < (unsigned short)((f ? 122 : 0) ^ (a ? c : 0)) - 64055;
+         e += 3)
+      arr_15[d] = 42;
+}
+int main() {
+    test(37, 8, 12325048486467861044ULL, 45936);
+    for (int i = 0; i < 8; ++i)
+      {
+        if (arr_15[i] != ((i&1) ? 0 : 42))
+          __builtin_abort();
+      }
+  return 0;
+}
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/ssa-dom-thread-14.c b/gcc/testsuite/gcc.dg/tree-ssa/ssa-dom-thread-14.c
index 3bc4b3795cb..a25fe8bd89e 100644
--- a/gcc/testsuite/gcc.dg/tree-ssa/ssa-dom-thread-14.c
+++ b/gcc/testsuite/gcc.dg/tree-ssa/ssa-dom-thread-14.c
@@ -37,5 +37,5 @@ expand_shift_1 (int code, int unsignedp, int rotate,
    we will enter the TRUE arm of the conditional and we can thread
    the test to compute the first first argument of the expand_binop
    call if we look backwards through the boolean logicals.  */
-/* { dg-final { scan-tree-dump-times "Threaded" 1 "dom2"} } */
+/* { dg-final { scan-tree-dump-times "Threaded" 2 "dom2"} } */