[gcc r11-3726] tree-optimization/97330 - fix bad load sinking

[gcc r11-3726] tree-optimization/97330 - fix bad load sinking

[Richard Biener]

https://gcc.gnu.org/g:629e0547af33221a925f38757b52a9284148b68a

commit r11-3726-g629e0547af33221a925f38757b52a9284148b68a
Author: Richard Biener <rguenther@suse.de>
Date:   Thu Oct 8 13:18:57 2020 +0200

    tree-optimization/97330 - fix bad load sinking
    
    This fixes bad placement of sunk loads.
    
    2020-10-08  Richard Biener  <rguenther@suse.de>
    
            PR tree-optimization/97330
            * tree-ssa-sink.c (statement_sink_location): Avoid skipping
            PHIs when they dominate the insert location.
    
            * gcc.dg/torture/pr97330-1.c: New testcase.
            * gcc.dg/torture/pr97330-2.c: Likewise.

Diff:
---
 gcc/testsuite/gcc.dg/torture/pr97330-1.c | 19 +++++++++++++++++++
 gcc/testsuite/gcc.dg/torture/pr97330-2.c | 14 ++++++++++++++
 gcc/tree-ssa-sink.c                      |  4 +++-
 3 files changed, 36 insertions(+), 1 deletion(-)

diff --git a/gcc/testsuite/gcc.dg/torture/pr97330-1.c b/gcc/testsuite/gcc.dg/torture/pr97330-1.c
new file mode 100644
index 00000000000..7dce5bd90d4
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/torture/pr97330-1.c
@@ -0,0 +1,19 @@
+/* { dg-do compile } */
+
+typedef int a;
+typedef char b;
+int c;
+void d(e, f, dst, g, avail, h) int e;
+b *f, *dst;
+a g, avail;
+int h;
+{
+  b i = *f;
+  if (e)
+    goto j;
+  while (avail) {
+    *dst = i;
+  j:
+    avail -= c;
+  }
+}
diff --git a/gcc/testsuite/gcc.dg/torture/pr97330-2.c b/gcc/testsuite/gcc.dg/torture/pr97330-2.c
new file mode 100644
index 00000000000..a0644831cfd
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/torture/pr97330-2.c
@@ -0,0 +1,14 @@
+/* { dg-do compile } */
+
+int a, b, d;
+char c, e;
+void f(void) {
+  char g = c;
+  if (b)
+    goto h;
+  while (d) {
+    e = c;
+  h:
+    d -= a;
+  }
+}
diff --git a/gcc/tree-ssa-sink.c b/gcc/tree-ssa-sink.c
index ba8e5577e9c..207aae2818a 100644
--- a/gcc/tree-ssa-sink.c
+++ b/gcc/tree-ssa-sink.c
@@ -391,8 +391,10 @@ statement_sink_location (gimple *stmt, basic_block frombb,
 	      if (gimple_code (use_stmt) == GIMPLE_PHI)
 		{
 		  /* In case the PHI node post-dominates the current insert location
-		     we can disregard it.  */
+		     we can disregard it.  But make sure it is not dominating
+		     it as well as can happen in a CFG cycle.  */
 		  if (commondom != bb
+		      && !dominated_by_p (CDI_DOMINATORS, commondom, bb)
 		      && dominated_by_p (CDI_POST_DOMINATORS, commondom, bb))
 		    continue;
 		  bb = EDGE_PRED (bb, PHI_ARG_INDEX_FROM_USE (use_p))->src;