tree-ssa-reassoc.c (should_break_up_subtract): Also break up if the use is in USE - X.

2017-08-03  Richard Biener  <rguenther@suse.de>

	* tree-ssa-reassoc.c (should_break_up_subtract): Also break
	up if the use is in USE - X.

	* gcc.dg/tree-ssa/reassoc-23.c: Adjust to fool early folding
	and CSE.

From-SVN: r250855

gcc/ChangeLog

+2017-08-03  Richard Biener  <rguenther@suse.de>
+
+	* tree-ssa-reassoc.c (should_break_up_subtract): Also break
+	up if the use is in USE - X.
+
 2017-08-03 Alexander Monakov  <amonakov@ispras.ru>
 
 	* toplev.c (dumpfile.h): New include.

gcc/testsuite/ChangeLog

 2017-08-03  Richard Biener  <rguenther@suse.de>
 
+	* gcc.dg/tree-ssa/reassoc-23.c: Adjust to fool early folding
+	and CSE.
+
+2017-08-03 Richard Biener  <rguenther@suse.de>
+
 	PR middle-end/81148
 	* c-c++-common/ubsan/pr81148.c: New testcase.
 

gcc/testsuite/gcc.dg/tree-ssa/reassoc-23.c

@@ -6,9 +6,10 @@ foo(unsigned int a, unsigned int b, unsigned int c, unsigned int d,
     unsigned int e, unsigned int f, unsigned int g, unsigned int h)
 {
   /* Should be transformed into e = 20 */
-  unsigned int i = (a + 9) + (c + 8);
-  unsigned int j = (-c + 1) + (-a + 2);
-
+  unsigned int i = (a + 9);
+  unsigned int j = (-c + 1);
+  i += (c + 8);
+  j += (-a + 2);
   e = i + j;
   return e;
 }

gcc/tree-ssa-reassoc.c

@@ -4729,6 +4729,8 @@ should_break_up_subtract (gimple *stmt)
       && (immusestmt = get_single_immediate_use (lhs))
       && is_gimple_assign (immusestmt)
       && (gimple_assign_rhs_code (immusestmt) == PLUS_EXPR
+	  || (gimple_assign_rhs_code (immusestmt) == MINUS_EXPR
+	      && gimple_assign_rhs1 (immusestmt) == lhs)
 	  || gimple_assign_rhs_code (immusestmt) == MULT_EXPR))
     return true;
   return false;