re PR target/77478 (Incorrect code generated with -O3, m32, -msse2 and -ffast-math)

2016-09-27  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/77478
	* tree-vect-loop-manip.c (vect_gen_niters_for_prolog_loop):
	Fix alignment of SSA var used before the alignment prologue.

	* gcc.dg/torture/pr77478.c: New testcase.

From-SVN: r240532

gcc/ChangeLog

@@ -1,3 +1,9 @@
+2016-09-27  Richard Biener  <rguenther@suse.de>
+
+	PR tree-optimization/77478
+	* tree-vect-loop-manip.c (vect_gen_niters_for_prolog_loop):
+	Fix alignment of SSA var used before the alignment prologue.
+
 2016-09-27  Senthil Kumar Selvaraj  <senthil_kumar.selvaraj@atmel.com>
 
 	Backport from trunk r227496

gcc/testsuite/ChangeLog

@@ -1,3 +1,8 @@
+2016-09-27  Richard Biener  <rguenther@suse.de>
+
+	PR tree-optimization/77478
+	* gcc.dg/torture/pr77478.c: New testcase.
+
 2016-09-27  Senthil Kumar Selvaraj  <senthil_kumar.selvaraj@atmel.com>
 
 	Backport from trunk r227496

gcc/testsuite/gcc.dg/torture/pr77478.c

@@ -0,0 +1,22 @@
+/* { dg-do run } */
+/* { dg-additional-options "-ffast-math" } */
+
+static const float A[10] = {1};
+
+float
+foo(float *f, int n)
+{
+  int i, j;
+  float a = 0, b = 0;
+  for (i = n/2; i < n; i++)
+    a += f[i]*.1f;
+  for (i = n/2, j = 0; i < n; i++, j++)
+    b += f[i]*A[j]+a*A[j];
+  return b;
+}
+
+int main()
+{
+  float a[21] = {0};
+  return foo(a+1, 20) + foo(a, 20);
+}

gcc/tree-vect-loop-manip.c

@@ -1886,7 +1886,7 @@ vect_gen_niters_for_prolog_loop (loop_vec_info loop_vinfo, tree loop_niters, int
       gimple_seq new_stmts = NULL;
       bool negative = tree_int_cst_compare (DR_STEP (dr), size_zero_node) < 0;
       tree offset = negative
-	  ? size_int (-TYPE_VECTOR_SUBPARTS (vectype) + 1) : NULL_TREE;
+	  ? size_int (-TYPE_VECTOR_SUBPARTS (vectype) + 1) : size_zero_node;
       tree start_addr = vect_create_addr_base_for_vector_ref (dr_stmt,
 						&new_stmts, offset, loop);
       tree type = unsigned_type_for (TREE_TYPE (start_addr));