[PATCH] D121455: [clang][dataflow] Add support for nested composite bool expressions

[Stanislav Gatev via Phabricator via cfe-commits]

sgatev added inline comments.


================
Comment at: clang/lib/Analysis/FlowSensitive/Transfer.cpp:516
+    // assigned to it.
+    Visit(&SubExpr);
+    if (auto *Val = dyn_cast_or_null<BoolValue>(
----------------
xazax.hun wrote:
> Could you elaborate on when would this happen? I'd expect the traversal to always visit the predecessor basic blocks first and within a basic block always visit subexpressions first. So I'd be quite surprised if there is a subexpression we did not visit.
>From what I've seen, logic operators influence the structure of the CFG through additional basic blocks and terminators, but their sub-expression operators are not added directly in the basic blocks.

For example:
```
void test(bool a, bool b, bool c) {
    bool d = a && (b || c);
}
```

results in:
```

void test(bool a, bool b, bool c)
 [B5 (ENTRY)]
   Succs (1): B4

 [B1]
   1: [B4.2] && ([B3.2] || [B2.2])
   2: bool d = a && (b || c);
   Preds (3): B2 B3 B4
   Succs (1): B0

 [B2]
   1: c
   2: [B2.1] (ImplicitCastExpr, LValueToRValue, _Bool)
   Preds (1): B3
   Succs (1): B1

 [B3]
   1: b
   2: [B3.1] (ImplicitCastExpr, LValueToRValue, _Bool)
   T: [B3.2] || ...
   Preds (1): B4
   Succs (2): B1 B2

 [B4]
   1: a
   2: [B4.1] (ImplicitCastExpr, LValueToRValue, _Bool)
   T: [B4.2] && ...
   Preds (1): B5
   Succs (2): B3 B1

 [B0 (EXIT)]
   Preds (1): B1
```

So, when we evaluate `a && (b || c)` in `B1`, the sub-expression `b || c` has not been evaluated yet. I updated the comment in the code to make that more clear.


Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D121455/new/

https://reviews.llvm.org/D121455