[COMMITTED] PR tree-optimization/122756 - Avoid recursion with SCEV

[Andrew MacLeod]

Now that SCEV is calling ranger for values, we need to make sure ranger 
doesnt call back into SCEV again or we get infinite loops like this PR.

fold_using_range::range_of_ssa_name_with_loop_info   tries to use SCEV 
to see if it can refinea PHI result based on loop information. This 
patch adds a flag aroudn that call so that if the call into SCEV calls 
back into ranger, we won't re-invoke SCEV again.

Bootstraps on x86_64-pc-linux-gnu with npo regressions, and the test now 
builds on a riscv64 cross compiler.   I think I got the condition on the 
testcase right, please fix them if not :-P. Pushed.

Andrew


From 00c16753875ddd9fcc9a6484717a1fc6dc95b691 Mon Sep 17 00:00:00 2001
From: Andrew MacLeod <amacl...@redhat.com>
Date: Wed, 19 Nov 2025 11:31:16 -0500
Subject: [PATCH] Avoid recursion with SCEV

Ranger should not invoke SCEV if its already in the middle of a SCEV call.

	PR tree-optimization/122756
	gcc/
	* gimple-range-fold.cc (range_of_ssa_name_with_loop_info): Do
	not invoke SCEV if already in a SCEV call.

	gcc/testsuite/
	* gcc.dg/pr122756.c: New.
---
 gcc/gimple-range-fold.cc        | 15 ++++++++++++---
 gcc/testsuite/gcc.dg/pr122756.c | 15 +++++++++++++++
 2 files changed, 27 insertions(+), 3 deletions(-)
 create mode 100644 gcc/testsuite/gcc.dg/pr122756.c

diff --git a/gcc/gimple-range-fold.cc b/gcc/gimple-range-fold.cc
index 63e114e4d04..bd5e53516b7 100644
--- a/gcc/gimple-range-fold.cc
+++ b/gcc/gimple-range-fold.cc
@@ -1252,11 +1252,15 @@ fold_using_range::range_of_ssa_name_with_loop_info (vrange &r, tree name,
 						    class loop *l, gphi *phi,
 						    fur_source &src)
 {
+  static bool in_scev_call = false;
   gcc_checking_assert (TREE_CODE (name) == SSA_NAME);
+  // Avoid SCEV callbacks causing infinite recursion.
+  if (in_scev_call)
+    r.set_varying (TREE_TYPE (name));
   // SCEV currently invokes get_range_query () for values.  If the query
   // being passed in is not the same SCEV will use, do not invoke SCEV.
   // This can be remove if/when SCEV uses a passed in range-query.
-  if (src.query () != get_range_query (cfun))
+  else if (src.query () != get_range_query (cfun))
     {
       r.set_varying (TREE_TYPE (name));
       // Report the msmatch if SRC is not the global query.  The cache
@@ -1266,8 +1270,13 @@ fold_using_range::range_of_ssa_name_with_loop_info (vrange &r, tree name,
 	fprintf (dump_file,
 	  "fold_using-range:: SCEV not invoked due to mismatched queries\n");
     }
-  else if (!range_of_var_in_loop (r, name, l, phi, src.query ()))
-      r.set_varying (TREE_TYPE (name));
+  else
+    {
+      in_scev_call = true;
+      if (!range_of_var_in_loop (r, name, l, phi, src.query ()))
+	r.set_varying (TREE_TYPE (name));
+      in_scev_call = false;
+    }
 }
 
 // -----------------------------------------------------------------------
diff --git a/gcc/testsuite/gcc.dg/pr122756.c b/gcc/testsuite/gcc.dg/pr122756.c
new file mode 100644
index 00000000000..62994696ac8
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr122756.c
@@ -0,0 +1,15 @@
+/* { dg-do compile } */
+/* { dg-options "-O3" } */
+/* { dg-additional-options "-march=rv64gcv -mabi=lp64d" { target { rv64 } } } */
+
+long a;
+void b() {
+  unsigned long c, d;
+  for (;; c = d + 2000) {
+    d = c;
+    for (; d < a; d += 2)
+      if (d % 2)
+        for (;;)
+          ;
+  }
+}
-- 
2.45.0