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Improve do_store_flag for comparing single bit against that bit

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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.
This commit is contained in:
Andrew Pinski 2023-05-18 22:17:07 +00:00
parent 908e5ab5c1
commit 6cf856f873
1 changed files with 8 additions and 3 deletions
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11
gcc/expr.cc
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@ -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,