tree-optimization/112636 - estimate niters before header copying

The following avoids a mismatch between an early query for maximum
number of iterations of a loop and a late one when through ranger
we'd get iterations estimated.  Instead make sure we compute niters
before querying the iteration bound.

	PR tree-optimization/112636
	* tree-ssa-loop-ch.cc (ch_base::copy_headers): Call
	estimate_numbers_of_iterations before querying
	get_max_loop_iterations_int.
	(pass_ch::execute): Initialize SCEV and loops appropriately.

	* gcc.dg/pr112636.c: New testcase.

2 files changed, 27 insertions, 11 deletions

diff --git a/gcc/testsuite/gcc.dg/pr112636.c b/gcc/testsuite/gcc.dg/pr112636.c
new file mode 100644
index 0000000..284ae8f
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr112636.c
@@ -0,0 +1,13 @@
+/* { dg-do compile } */
+/* { dg-options "-O -ftree-vectorize" } */
+
+int a[1], b;
+unsigned c;
+int main() {
+  while (b) {
+    if (a[c])
+      break;
+    c--;
+  }
+  return 0;
+}
diff --git a/gcc/tree-ssa-loop-ch.cc b/gcc/tree-ssa-loop-ch.cc
index 3ce5cc2..6c6e562 100644
--- a/gcc/tree-ssa-loop-ch.cc
+++ b/gcc/tree-ssa-loop-ch.cc
@@ -41,6 +41,8 @@ along with GCC; see the file COPYING3.  If not see
 #include "gimple-pretty-print.h"
 #include "cfganal.h"
 #include "tree-ssa-loop-manip.h"
+#include "tree-ssa-loop-niter.h"
+#include "tree-scalar-evolution.h"
 
 /* Return path query insteance for testing ranges of statements
    in headers of LOOP contained in basic block BB.
@@ -797,7 +799,16 @@ ch_base::copy_headers (function *fun)
 	fprintf (dump_file,
 		 "Analyzing loop %i\n", loop->num);
 
+      /* If the loop is already a do-while style one (either because it was
+	 written as such, or because jump threading transformed it into one),
+	 we might be in fact peeling the first iteration of the loop.  This
+	 in general is not a good idea.  Also avoid touching infinite loops.  */
+      if (!loop_has_exit_edges (loop)
+	  || !process_loop_p (loop))
+	continue;
+
       basic_block header = loop->header;
+      estimate_numbers_of_iterations (loop);
       if (!get_max_loop_iterations_int (loop))
 	{
 	  if (dump_file && (dump_flags & TDF_DETAILS))
@@ -808,14 +819,6 @@ ch_base::copy_headers (function *fun)
 	  continue;
 	}
 
-      /* If the loop is already a do-while style one (either because it was
-	 written as such, or because jump threading transformed it into one),
-	 we might be in fact peeling the first iteration of the loop.  This
-	 in general is not a good idea.  Also avoid touching infinite loops.  */
-      if (!loop_has_exit_edges (loop)
-	  || !process_loop_p (loop))
-	continue;
-
       /* Iterate the header copying up to limit; this takes care of the cases
 	 like while (a && b) {...}, where we want to have both of the conditions
 	 copied.  TODO -- handle while (a || b) - like cases, by not requiring
@@ -1170,12 +1173,12 @@ ch_base::copy_headers (function *fun)
 unsigned int
 pass_ch::execute (function *fun)
 {
-  loop_optimizer_init (LOOPS_HAVE_PREHEADERS
-		       | LOOPS_HAVE_SIMPLE_LATCHES
-		       | LOOPS_HAVE_RECORDED_EXITS);
+  loop_optimizer_init (LOOPS_NORMAL | LOOPS_HAVE_RECORDED_EXITS);
+  scev_initialize ();
 
   unsigned int res = copy_headers (fun);
 
+  scev_finalize ();
   loop_optimizer_finalize ();
   return res;
 }