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Simple reassoc transforms in match.pd


Hello,

here are a few simple transformations, mostly useful for types with undefined overflow where we do not have reassoc.

I did not name the testcase reassoc-* to leave that namespace to the realloc pass, and -fno-tree-reassoc is just in case someone ever enhances that pass...

Bootstrap + testsuite on powerpc64le-unknown-linux-gnu.

2017-06-23  Marc Glisse  <marc.glisse@inria.fr>

gcc/
	* match.pd ((A+-B)+(C-A), (A+B)-(A-C)): New transformations.

gcc/testsuite/
	* gcc.dg/tree-ssa/assoc-1.c: New file.

--
Marc Glisse
Index: gcc/match.pd
===================================================================
--- gcc/match.pd	(revision 249585)
+++ gcc/match.pd	(working copy)
@@ -1314,20 +1314,32 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
     (negate @1))
   (simplify
     (plus:c (minus @0 @1) @1)
     @0)
   (simplify
    (minus @0 (plus:c @0 @1))
    (negate @1))
   (simplify
    (minus @0 (minus @0 @1))
    @1)
+  /* (A +- B) + (C - A)   -> C +- B */
+  /* (A +  B) - (A - C)   -> B + C */
+  /* More cases are handled with comparisons.  */
+  (simplify
+   (plus:c (plus:c @0 @1) (minus @2 @0))
+   (plus @2 @1))
+  (simplify
+   (plus:c (minus @0 @1) (minus @2 @0))
+   (minus @2 @1))
+  (simplify
+   (minus (plus:c @0 @1) (minus @0 @2))
+   (plus @1 @2))
 
   /* (A +- CST1) +- CST2 -> A + CST3
      Use view_convert because it is safe for vectors and equivalent for
      scalars.  */
   (for outer_op (plus minus)
    (for inner_op (plus minus)
 	neg_inner_op (minus plus)
     (simplify
      (outer_op (nop_convert (inner_op @0 CONSTANT_CLASS_P@1))
 	       CONSTANT_CLASS_P@2)
Index: gcc/testsuite/gcc.dg/tree-ssa/assoc-1.c
===================================================================
--- gcc/testsuite/gcc.dg/tree-ssa/assoc-1.c	(nonexistent)
+++ gcc/testsuite/gcc.dg/tree-ssa/assoc-1.c	(working copy)
@@ -0,0 +1,31 @@
+/* { dg-do compile } */
+/* { dg-options "-O -fdump-tree-optimized-raw -fno-tree-reassoc" } */
+
+int f0(int a,int b,int c){
+  int d = a + b;
+  int e = c + b;
+  return d - e;
+}
+int f1(int a,int b,int c){
+  int d = a + b;
+  int e = b - c;
+  return d - e;
+}
+int f2(int a,int b,int c){
+  int d = a + b;
+  int e = c - b;
+  return e + d;
+}
+int f3(int a,int b,int c){
+  int d = a - b;
+  int e = c - b;
+  return d - e;
+}
+int f4(int a,int b,int c){
+  int d = b - a;
+  int e = c - b;
+  return e + d;
+}
+
+/* { dg-final { scan-tree-dump-times "plus_expr" 2 "optimized" } } */
+/* { dg-final { scan-tree-dump-times "minus_expr" 3 "optimized" } } */

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