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update Liveness to detect that safety checks do not modify memory

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followup to [25d3713b07a100d8fdb349317db97fd9d0c1e366]
Resolves #12215

Previous code didn't account for the extra unreach() that now exists in the air:

```
 %29!= block(void, {
    %30!= cond_br(%22!, {
      %31!= br(%29, @Air.Inst.Ref.void_value)
    }, {
      %2! %15!
      %27!= call(%26, [%19!, %21])
      %28!= unreach()
    })
  } %22!)
```
This commit is contained in:
Xavier Bouchoux 2023-06-24 10:47:20 +00:00 committed by Andrew Kelley
parent a5e15eced0
commit f10b9e8fd7
1 changed files with 9 additions and 2 deletions
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11
src/Liveness.zig
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@ -621,11 +621,18 @@ pub fn categorizeOperand(
if (inst_data.operand == operand_ref and operandDies(l, body[0], 0))
return .tomb;
if (cond_extra.data.then_body_len != 1 or cond_extra.data.else_body_len != 1)
if (cond_extra.data.then_body_len > 2 or cond_extra.data.else_body_len > 2)
return .complex;
const then_body = air.extra[cond_extra.end..][0..cond_extra.data.then_body_len];
const else_body = air.extra[cond_extra.end + cond_extra.data.then_body_len ..][0 .. cond_extra.data.then_body_len + cond_extra.data.else_body_len];
if (then_body.len > 1 and air_tags[then_body[1]] != .unreach)
return .complex;
if (else_body.len > 1 and air_tags[else_body[1]] != .unreach)
return .complex;
var operand_live: bool = true;
for (air.extra[cond_extra.end..][0..2]) |cond_inst| {
for (&[_]u32{ then_body[0], else_body[0] }) |cond_inst| {
if (l.categorizeOperand(air, cond_inst, operand, ip) == .tomb)
operand_live = false;