[PATCH] fold-const: Handle AND, IOR, XOR with stepped vectors [PR112971].

[Robin Dapp]

Hi,

found in PR112971, this patch adds folding support for bitwise operations
of const duplicate zero vectors and stepped vectors.
On riscv we have the situation that a folding would perpetually continue
without simplifying because e.g. {0, 0, 0, ...} & {7, 6, 5, ...} would
not fold to {0, 0, 0, ...}.

Bootstrapped and regtested on x86 and aarch64, regtested on riscv.

I won't be available to respond quickly until next year.  Pan or Juzhe,
as discussed, feel free to continue with possible revisions.

Regards
 Robin


gcc/ChangeLog:

        PR middle-end/112971

        * fold-const.cc (const_binop): Handle
        zerop@1  AND/IOR/XOR  VECT_CST_STEPPED_P@2

gcc/testsuite/ChangeLog:

        * gcc.target/riscv/rvv/autovec/pr112971.c: New test.
---
 gcc/fold-const.cc                              | 14 +++++++++++++-
 .../gcc.target/riscv/rvv/autovec/pr112971.c    | 18 ++++++++++++++++++
 2 files changed, 31 insertions(+), 1 deletion(-)
 create mode 100644 gcc/testsuite/gcc.target/riscv/rvv/autovec/pr112971.c

diff --git a/gcc/fold-const.cc b/gcc/fold-const.cc
index f5d68ac323a..43ed097bf5c 100644
--- a/gcc/fold-const.cc
+++ b/gcc/fold-const.cc
@@ -1653,8 +1653,20 @@ const_binop (enum tree_code code, tree arg1, tree arg2)
     {
       tree type = TREE_TYPE (arg1);
       bool step_ok_p;
+
+      /* AND, IOR as well as XOR with a zerop can be handled directly.  */
       if (VECTOR_CST_STEPPED_P (arg1)
-         && VECTOR_CST_STEPPED_P (arg2))
+         && VECTOR_CST_DUPLICATE_P (arg2)
+         && integer_zerop (VECTOR_CST_ELT (arg2, 0)))
+       step_ok_p = code == BIT_AND_EXPR || code == BIT_IOR_EXPR
+         || code == BIT_XOR_EXPR;
+      else if (VECTOR_CST_STEPPED_P (arg2)
+              && VECTOR_CST_DUPLICATE_P (arg1)
+              && integer_zerop (VECTOR_CST_ELT (arg1, 0)))
+       step_ok_p = code == BIT_AND_EXPR || code == BIT_IOR_EXPR
+         || code == BIT_XOR_EXPR;
+      else if (VECTOR_CST_STEPPED_P (arg1)
+              && VECTOR_CST_STEPPED_P (arg2))
        /* We can operate directly on the encoding if:
 
              a3 - a2 == a2 - a1 && b3 - b2 == b2 - b1
diff --git a/gcc/testsuite/gcc.target/riscv/rvv/autovec/pr112971.c 
b/gcc/testsuite/gcc.target/riscv/rvv/autovec/pr112971.c
new file mode 100644
index 00000000000..816ebd3c493
--- /dev/null
+++ b/gcc/testsuite/gcc.target/riscv/rvv/autovec/pr112971.c
@@ -0,0 +1,18 @@
+/* { dg-do compile }  */
+/* { dg-options "-march=rv64gcv_zvl256b -mabi=lp64d -O3 -fno-vect-cost-model" 
}  */
+
+int a;
+short b[9];
+char c, d;
+void e() {
+  d = 0;
+  for (;; d++) {
+    if (b[d])
+      break;
+    a = 8;
+    for (; a >= 0; a--) {
+      char *f = &c;
+      *f &= d == (a & d);
+    }
+  }
+}
-- 
2.43.0