The following fixes an optimization regression noted in PR78546 where
moving patterns from forwprop to match.pd missed one variant.
Bootstrap & regtest running on x86_64-unknown-linux-gnu.
Richard.
2016-11-28 Richard Biener <rguent...@suse.de>
PR middle-end/78546
* match.pd: Add CST - (CST - A) -> CST - A missing case.
* gcc.dg/tree-ssa/forwprop-36.c: New testcase.
diff --git a/gcc/match.pd b/gcc/match.pd
index 2d4e019..9e5df64 100644
--- a/gcc/match.pd
+++ b/gcc/match.pd
@@ -1216,6 +1216,13 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
(if (cst && !TREE_OVERFLOW (cst))
(minus { cst; } @0)))))
+ /* CST - (CST - A) -> CST - A */
+ (simplify
+ (minus CONSTANT_CLASS_P@1 (minus CONSTANT_CLASS_P@2 @0))
+ (with { tree cst = const_binop (MINUS_EXPR, type, @1, @2); }
+ (if (cst && !TREE_OVERFLOW (cst))
+ (minus { cst; } @0))))
+
/* ~A + A -> -1 */
(simplify
(plus:c (bit_not @0) @0)
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/forwprop-36.c
b/gcc/testsuite/gcc.dg/tree-ssa/forwprop-36.c
new file mode 100644
index 0000000..9de73ff
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/forwprop-36.c
@@ -0,0 +1,24 @@
+/* { dg-do compile { target int128 } } */
+/* { dg-options "-O -fdump-tree-cddce1" } */
+
+typedef unsigned __int128 u128;
+
+u128 a, b;
+
+static inline u128
+foo (u128 p1)
+{
+ p1 += ~b;
+ return -p1;
+}
+
+int
+main ()
+{
+ u128 x = foo (~0x7fffffffffffffff);
+ if (x != 0x8000000000000001)
+ __builtin_abort();
+ return 0;
+}
+
+/* { dg-final { scan-tree-dump "if \\(b.0_\[0-9\]+ != 0\\)" "cddce1" } } */
