[PATCH] IRA: Ignore debug insns for uses in split_live_ranges_for_shrink_wrap. [PR116179]

[Andrew Pinski]

Late_combine exposed this latent bug in split_live_ranges_for_shrink_wrap.
What it did was copy-prop regno 151 from regno 119 from:
```
(insn 2 264 3 2 (set (reg/f:DI 119 [ thisD.3697 ])
        (reg:DI 151)) "/app/example.cpp":19:13 70 {*movdi_aarch64}
     (expr_list:REG_DEAD (reg:DI 151)
        (nil)))
```

into these insns:
```
(debug_insn 147 146 148 5 (var_location:DI thisD.3727 (reg/f:DI 119 [ 
thisD.3697 ])) "/app/example.cpp":21:5 -1
     (nil))
....
(insn 167 166 168 7 (set (reg:DI 1 x1)
        (reg/f:DI 119 [ thisD.3697 ])) "/app/example.cpp":14:21 70 
{*movdi_aarch64}
     (nil))
```

Both are valid things to do. The problem is split_live_ranges_for_shrink_wrap 
looks at the
uses of reg 151 and with and without debugging reg 151 have a different usage 
in different BBs.
The function is trying to find a splitting point for reg 151 and they are 
different. In the end
this causes register allocation difference.
The fix is for split_live_ranges_for_shrink_wrap to ignore uses that were in 
debug insns.

Bootstrappped and tested on x86_64-linux-gnu with no regressions.

        PR rtl-optimization/116179

gcc/ChangeLog:

        * ira.cc (split_live_ranges_for_shrink_wrap): For the uses loop,
        only look at non-debug insns.

gcc/testsuite/ChangeLog:

        * g++.dg/torture/pr116179-1.C: New test.

Signed-off-by: Andrew Pinski <quic_apin...@quicinc.com>
---
 gcc/ira.cc                                |  4 +++-
 gcc/testsuite/g++.dg/torture/pr116179-1.C | 26 +++++++++++++++++++++++
 2 files changed, 29 insertions(+), 1 deletion(-)
 create mode 100644 gcc/testsuite/g++.dg/torture/pr116179-1.C

diff --git a/gcc/ira.cc b/gcc/ira.cc
index 5642aea3caa..5a04231f7bd 100644
--- a/gcc/ira.cc
+++ b/gcc/ira.cc
@@ -5144,7 +5144,9 @@ split_live_ranges_for_shrink_wrap (void)
           use = DF_REF_NEXT_REG (use))
        {
          int ubbi = DF_REF_BB (use)->index;
-         if (bitmap_bit_p (reachable, ubbi))
+         /* Only non debug insn should not be taken into account.  */
+         if (NONDEBUG_INSN_P (DF_REF_INSN (use))
+             && bitmap_bit_p (reachable, ubbi))
            bitmap_set_bit (need_new, ubbi);
        }
       last_interesting_insn = insn;
diff --git a/gcc/testsuite/g++.dg/torture/pr116179-1.C 
b/gcc/testsuite/g++.dg/torture/pr116179-1.C
new file mode 100644
index 00000000000..85e63c5938f
--- /dev/null
+++ b/gcc/testsuite/g++.dg/torture/pr116179-1.C
@@ -0,0 +1,26 @@
+/* { dg-additional-options "-fcompare-debug" } */
+
+/* PR rtl-optimization/116179 */
+
+struct g *b;
+struct g {};
+void *operator new(__SIZE_TYPE__, void *);
+enum c {};
+struct d : g{} * e;
+c f;
+struct h {
+  g *k() {
+    d *a;
+    c i;
+    if (a || i == 0 || i == 1)
+      if (e || f)
+        return 0;
+    return new (&j) d;
+  }
+  void n();
+  g j;
+};
+void h::n() {
+  for (g *l(b), *m(b); l; l = m, m = 0)
+    k();
+}
-- 
2.43.0