diff mbox series

[2/2] Improve do_store_flag for comparing single bit against that bit

Message ID 20230519021410.1841811-2-apinski@marvell.com
State Accepted
Headers
Series [1/2] Improve do_store_flag for single bit comparison against 0 |

Checks

Context Check Description
snail/gcc-patch-check success Github commit url

Commit Message

Andrew Pinski May 19, 2023, 2:14 a.m. UTC 
  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.

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.
---
 gcc/expr.cc | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

Comments

Jeff Law May 19, 2023, 4:45 p.m. UTC | #1 
On 5/18/23 20:14, Andrew Pinski via Gcc-patches wrote:
> 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.
> 
> 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.
This looks like it can/should go forward independently of 1/2 and 
touches on my earlier comment about using bit extractions  ;-)

So OK by me.

jeff
diff mbox series

Patch

diff --git a/gcc/expr.cc b/gcc/expr.cc
index 91528e734e7..a4628c51c0c 100644
--- a/gcc/expr.cc
+++ b/gcc/expr.cc
@@ -13080,12 +13080,15 @@  do_store_flag (sepops ops, rtx target, machine_mode mode)
      so we just call into the folder and expand its result.  */
 
   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;
 	  tree op1;
@@ -13103,11 +13106,13 @@  do_store_flag (sepops ops, rtx target, machine_mode mode)
 	      op0 = arg0;
 	      op1 = wide_int_to_tree (TREE_TYPE (op0), 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);
 	  tree temp = fold_build2_loc (loc, BIT_AND_EXPR, TREE_TYPE (op0),
 				       op0, op1);
-	  temp = fold_single_bit_test (loc, tcode, temp, arg1, type);
+	  temp = fold_single_bit_test (loc, tcode, temp, build_zero_cst (type), type);
 	  if (temp)
 	    return expand_expr (temp, target, VOIDmode, EXPAND_NORMAL);
 	}