[gcc r14-1535] Improve do_store_flag for comparing single bit against that bit

[gcc r14-1535] Improve do_store_flag for comparing single bit against that bit

[Andrew Pinski]

https://gcc.gnu.org/g:6cf856f873c1a2ab39d8fb0a93b5f4505a22feb6

commit r14-1535-g6cf856f873c1a2ab39d8fb0a93b5f4505a22feb6
Author: Andrew Pinski <apinski@marvell.com>
Date:   Thu May 18 22:17:07 2023 +0000

    Improve do_store_flag for comparing single bit against that bit
    
    This is a case which I noticed while working on the previous patch.
    Sometimes we end up with `a == CST` instead of comparing against 0.
    This happens in the following code:
    ```
    unsigned f(unsigned t)
    {
      if (t & ~(1<<30)) __builtin_unreachable();
      t ^= (1<<30);
      return t != 0;
    }
    ```
    
    We should handle the case where the nonzero bits is the same as the
    comparison operand.
    
    Changes from v1:
    * v2: Updated for the bit extraction changes.
    
    OK? Bootstrapped and tested on x86_64-linux-gnu.
    
    gcc/ChangeLog:
    
            * expr.cc (do_store_flag): Improve for single bit testing
            not against zero but against that single bit.

Diff:
---
 gcc/expr.cc | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/gcc/expr.cc b/gcc/expr.cc
index 6027e7ffca5..58f5fe76372 100644
--- a/gcc/expr.cc
+++ b/gcc/expr.cc
@@ -13159,12 +13159,15 @@ do_store_flag (sepops ops, rtx target, machine_mode mode)
      than an scc insn even if we have it.  */
 
   if ((code == NE || code == EQ)
-      && integer_zerop (arg1)
+      && (integer_zerop (arg1)
+	  || integer_pow2p (arg1))
       && (TYPE_PRECISION (ops->type) != 1 || TYPE_UNSIGNED (ops->type)))
     {
       wide_int nz = tree_nonzero_bits (arg0);
 
-      if (wi::popcount (nz) == 1)
+      if (wi::popcount (nz) == 1
+	  && (integer_zerop (arg1)
+	      || wi::to_wide (arg1) == nz))
 	{
 	  tree op0;
 	  int bitnum;
@@ -13182,7 +13185,9 @@ do_store_flag (sepops ops, rtx target, machine_mode mode)
 	      op0 = arg0;
 	      bitnum = wi::exact_log2 (nz);
 	    }
-	  enum tree_code tcode = code == NE ? NE_EXPR : EQ_EXPR;
+	  enum tree_code tcode = EQ_EXPR;
+	  if ((code == NE) ^ !integer_zerop (arg1))
+	    tcode = NE_EXPR;
 
 	  type = lang_hooks.types.type_for_mode (mode, unsignedp);
 	  return expand_single_bit_test (loc, tcode,