tree-optimization: [PR103218] Fold ((type)(a<0)) << SIGNBITOFA into ((type)a) & signbit

This folds Fold ((type)(a<0)) << SIGNBITOFA into ((type)a) & signbit inside match.pd.
This was already handled in fold-cost by:
/* A < 0 ? <sign bit of A> : 0 is simply (A & <sign bit of A>).  */
I have not removed as we only simplify "a ? POW2 : 0" at the gimple level to "a << CST1"
and fold actually does the reverse of folding "(a<0)<<CST" into "(a<0) ? 1<<CST : 0".

OK? Bootstrapped and tested on x86_64-linux-gnu with no regressions.

	PR tree-optimization/103218

gcc/ChangeLog:

	* match.pd: New pattern for "((type)(a<0)) << SIGNBITOFA".

gcc/testsuite/ChangeLog:

	* gcc.dg/tree-ssa/pr103218-1.c: New test.

1 files changed, 28 insertions, 0 deletions

diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr103218-1.c b/gcc/testsuite/gcc.dg/tree-ssa/pr103218-1.c
new file mode 100644
index 0000000..f086f07
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/pr103218-1.c
@@ -0,0 +1,28 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-optimized" } */
+/* PR tree-optimization/103218 */
+
+/* These first two are removed during forwprop1 */
+signed char f(signed char a)
+{
+  signed char t = a < 0;
+  int tt = (unsigned char)(t << 7);
+  return tt;
+}
+signed char f0(signed char a)
+{
+  unsigned char t = a < 0;
+  int tt = (unsigned char)(t << 7);
+  return tt;
+}
+
+/* This one is removed during phiopt. */
+signed char  f1(signed char a)
+{
+    if (a < 0)
+      return 1u<<7;
+    return 0;
+}
+
+/* These three examples should remove "a < 0" by optimized. */
+/* { dg-final { scan-tree-dump-times "< 0" 0 "optimized"} } */