[gcc r12-5305] tree-optimization: [PR103218] Fold ((type)(a<0)) << SIGNBITOFA into ((type)a) & signbit

[gcc r12-5305] tree-optimization: [PR103218] Fold ((type)(a<0)) << SIGNBITOFA into ((type)a) & signbit

[Andrew Pinski]

https://gcc.gnu.org/g:11c4a06a6c1a9db0bfdb3ee8509392dd7163709c

commit r12-5305-g11c4a06a6c1a9db0bfdb3ee8509392dd7163709c
Author: Andrew Pinski <apinski@marvell.com>
Date:   Sat Nov 13 04:16:55 2021 +0000

    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.

Diff:
---
 gcc/match.pd                               | 10 ++++++++++
 gcc/testsuite/gcc.dg/tree-ssa/pr103218-1.c | 28 ++++++++++++++++++++++++++++
 2 files changed, 38 insertions(+)

diff --git a/gcc/match.pd b/gcc/match.pd
index 758322da217..7f76925b6c6 100644
--- a/gcc/match.pd
+++ b/gcc/match.pd
@@ -865,6 +865,16 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
     { tree utype = unsigned_type_for (type); }
     (convert (rshift (lshift (convert:utype @0) @2) @3))))))
 
+/* Fold ((type)(a<0)) << SIGNBITOFA into ((type)a) & signbit. */
+(simplify
+ (lshift (convert (lt @0 integer_zerop@1)) INTEGER_CST@2)
+ (if (TYPE_SIGN (TREE_TYPE (@0)) == SIGNED
+      && wi::eq_p (wi::to_wide (@2), TYPE_PRECISION (TREE_TYPE (@0)) - 1))
+  (with { wide_int wone = wi::one (TYPE_PRECISION (type)); }
+   (bit_and (convert @0)
+            { wide_int_to_tree (type,
+				wi::lshift (wone, wi::to_wide (@2))); }))))
+
 /* Fold (-x >> C) into -(x > 0) where C = precision(type) - 1.  */
 (for cst (INTEGER_CST VECTOR_CST)
  (simplify
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 00000000000..f086f073b38
--- /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"} } */