diff mbox series

tree-optimization/106809 - compile time hog in VN

Message ID 20220902123256.63A7B13328@imap2.suse-dmz.suse.de
State New, archived
Headers
Series tree-optimization/106809 - compile time hog in VN |

Commit Message

Richard Biener Sept. 2, 2022, 12:32 p.m. UTC 
  The dominated_by_p_w_unex function is prone to high compile time.
With GCC 12 we introduced a VN run for uninit diagnostics which now
runs into a degenerate case with bison generated code.  Fortunately
this case is easy to fix with a simple extra check - a more
general fix needs more work.

Bootstrapped and tested on x86_64-unknown-linux-gnu, pushed.

	PR tree-optimization/106809
	* tree-ssa-sccvn.cc (dominaged_by_p_w_unex): Check we have
	more than one successor before doing extra work.

	* gcc.dg/torture/pr106809.c: New testcase.
---
 gcc/testsuite/gcc.dg/torture/pr106809.c | 28 ++++++++++++
 gcc/tree-ssa-sccvn.cc                   | 57 +++++++++++++------------
 2 files changed, 58 insertions(+), 27 deletions(-)
 create mode 100644 gcc/testsuite/gcc.dg/torture/pr106809.c
diff mbox series

Patch

diff --git a/gcc/testsuite/gcc.dg/torture/pr106809.c b/gcc/testsuite/gcc.dg/torture/pr106809.c
new file mode 100644
index 00000000000..11e158185cf
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/torture/pr106809.c
@@ -0,0 +1,28 @@ 
+/* { dg-do compile } */
+/* { dg-additional-options "-Wuninitialized" } */
+
+int foo (int x, int *val)
+{
+  switch (x)
+    {
+#define C(n) \
+    case n + 0: return *val; \
+    case n + 1: return *val; \
+    case n + 2: return *val; \
+    case n + 3: return *val; \
+    case n + 4: return *val; \
+    case n + 5: return *val; \
+    case n + 6: return *val; \
+    case n + 7: return *val; \
+    case n + 8: return *val; \
+    case n + 9: return *val;
+#define C1(n) \
+    C(n+00) C(n+10) C(n+20) C(n+30) C(n+40) \
+    C(n+50) C(n+60) C(n+70) C(n+80) C(n+90)
+#define C10(n) \
+    C1(n+000) C1(n+100) C1(n+200) C1(n+300) C1(n+400) \
+    C1(n+500) C1(n+600) C1(n+700) C1(n+800) C1(n+900)
+    C10(1000)
+    }
+  return 0;
+}
diff --git a/gcc/tree-ssa-sccvn.cc b/gcc/tree-ssa-sccvn.cc
index a1f6f309609..5abc8667ce6 100644
--- a/gcc/tree-ssa-sccvn.cc
+++ b/gcc/tree-ssa-sccvn.cc
@@ -4877,41 +4877,44 @@  dominated_by_p_w_unex (basic_block bb1, basic_block bb2, bool allow_back)
     }
 
   /* Iterate to the single executable bb2 successor.  */
-  edge succe = NULL;
-  FOR_EACH_EDGE (e, ei, bb2->succs)
-    if ((e->flags & EDGE_EXECUTABLE)
-	|| (!allow_back && (e->flags & EDGE_DFS_BACK)))
-      {
-	if (succe)
-	  {
-	    succe = NULL;
-	    break;
-	  }
-	succe = e;
-      }
-  if (succe)
+  if (EDGE_COUNT (bb2->succs) > 1)
     {
-      /* Verify the reached block is only reached through succe.
-	 If there is only one edge we can spare us the dominator
-	 check and iterate directly.  */
-      if (EDGE_COUNT (succe->dest->preds) > 1)
-	{
-	  FOR_EACH_EDGE (e, ei, succe->dest->preds)
-	    if (e != succe
-		&& ((e->flags & EDGE_EXECUTABLE)
-		    || (!allow_back && (e->flags & EDGE_DFS_BACK))))
+      edge succe = NULL;
+      FOR_EACH_EDGE (e, ei, bb2->succs)
+	if ((e->flags & EDGE_EXECUTABLE)
+	    || (!allow_back && (e->flags & EDGE_DFS_BACK)))
+	  {
+	    if (succe)
 	      {
 		succe = NULL;
 		break;
 	      }
-	}
+	    succe = e;
+	  }
       if (succe)
 	{
-	  bb2 = succe->dest;
+	  /* Verify the reached block is only reached through succe.
+	     If there is only one edge we can spare us the dominator
+	     check and iterate directly.  */
+	  if (EDGE_COUNT (succe->dest->preds) > 1)
+	    {
+	      FOR_EACH_EDGE (e, ei, succe->dest->preds)
+		if (e != succe
+		    && ((e->flags & EDGE_EXECUTABLE)
+			|| (!allow_back && (e->flags & EDGE_DFS_BACK))))
+		  {
+		    succe = NULL;
+		    break;
+		  }
+	    }
+	  if (succe)
+	    {
+	      bb2 = succe->dest;
 
-	  /* Re-do the dominance check with changed bb2.  */
-	  if (dominated_by_p (CDI_DOMINATORS, bb1, bb2))
-	    return true;
+	      /* Re-do the dominance check with changed bb2.  */
+	      if (dominated_by_p (CDI_DOMINATORS, bb1, bb2))
+		return true;
+	    }
 	}
     }