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(-)
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);
}
--
2.31.1
