[gcc r15-7349] tree-optimization/117113 - ICE with unroll-and-jam

[Richard Biener via Gcc-cvs]

https://gcc.gnu.org/g:0675eb17480bada678bf2769d39732027abcd6d0

commit r15-7349-g0675eb17480bada678bf2769d39732027abcd6d0
Author: Richard Biener <rguent...@suse.de>
Date:   Mon Feb 3 15:12:52 2025 +0100

    tree-optimization/117113 - ICE with unroll-and-jam
    
    When there's an inner loop without virtual header PHI but the outer
    loop has one the fusion process cannot handle the need to create
    an inner loop virtual header PHI.  Punt in this case.
    
            PR tree-optimization/117113
            * gimple-loop-jam.cc (unroll_jam_possible_p): Detect when
            we cannot handle virtual SSA update.
    
            * gcc.dg/torture/pr117113.c: New testcase.

Diff:
---
 gcc/gimple-loop-jam.cc                  | 12 +++++++++++-
 gcc/testsuite/gcc.dg/torture/pr117113.c | 20 ++++++++++++++++++++
 2 files changed, 31 insertions(+), 1 deletion(-)

diff --git a/gcc/gimple-loop-jam.cc b/gcc/gimple-loop-jam.cc
index 9a2eba02dd97..5e6c04a7d7f2 100644
--- a/gcc/gimple-loop-jam.cc
+++ b/gcc/gimple-loop-jam.cc
@@ -279,13 +279,17 @@ unroll_jam_possible_p (class loop *outer, class loop 
*loop)
      body would be the after-iter value of the first body) if it's over
      an associative and commutative operation.  We wouldn't
      be able to handle unknown cycles.  */
+  bool inner_vdef = false;
   for (psi = gsi_start_phis (loop->header); !gsi_end_p (psi); gsi_next (&psi))
     {
       affine_iv iv;
       tree op = gimple_phi_result (psi.phi ());
 
       if (virtual_operand_p (op))
-       continue;
+       {
+         inner_vdef = true;
+         continue;
+       }
       if (!simple_iv (loop, loop, op, &iv, true))
        return false;
       /* The inductions must be regular, loop invariant step and initial
@@ -301,6 +305,12 @@ unroll_jam_possible_p (class loop *outer, class loop *loop)
         copy, _not_ the next value of the second body.  */
     }
 
+  /* When there's no inner loop virtual PHI IV we cannot handle the update
+     required to the inner loop if that doesn't already have one.  See
+     PR117113.  */
+  if (!inner_vdef && get_virtual_phi (outer->header))
+    return false;
+
   return true;
 }
 
diff --git a/gcc/testsuite/gcc.dg/torture/pr117113.c 
b/gcc/testsuite/gcc.dg/torture/pr117113.c
new file mode 100644
index 000000000000..e90ad034a4d3
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/torture/pr117113.c
@@ -0,0 +1,20 @@
+/* { dg-do compile } */
+/* { dg-additional-options "-fno-tree-dce -fno-inline" } */
+
+int a, b, c;
+volatile int d[1];
+void e() {}
+void f(int g) {}
+int main() {
+  int i;
+  for (; b; b--) {
+    for (i = 0; i < 3; i++) {
+      e();
+      f(d[0]);
+      d[0];
+    }
+    if (a)
+      c++;
+  }
+  return 0;
+}