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.
---
gcc/expr.cc | 11 ++++++++---
1 file changed, 8 insertions(+), 3 deletions(-)
diff --git a/gcc/expr.cc b/gcc/expr.cc
index b85e963b57e..e7e6112ff81 100644
--- a/gcc/expr.cc
+++ b/gcc/expr.cc
@@ -13152,12 +13152,15 @@ 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;
@@ -13175,7 +13178,9 @@ 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,
--
2.17.1
