ahatanak added inline comments.
================
Comment at: lib/CodeGen/CodeGenFunction.h:217
+ /// statements.
+ llvm::SmallVector<bool, 4> LabelSeenStack;
+
----------------
rjmccall wrote:
> Shouldn't this be maintained by some existing scoping structure like
> LexicalScope?
I think I need a structure that gets pushed and popped when we enter and exit a
compound statement, but I couldn't find one in CodeGenFunction.
Adding a flag to LexicalScope would fail to disable lifetime markers in some
cases. For example, in the code below (which I think is valid), the lifetime
markers of "i" wouldn't get disabled because a LexicalScope is pushed at the
beginning of CodeGenFunction::EmitForStmt:
```
void foo2(int *);
int c;
void foo1(int n) {
int *p = 0;
label1:
foo2(p);
for (int i = 0; i < n; ++i)
if (i == 5)
p = &i;
if (c)
goto label1;
}
```
If we want to avoid introducing new structures to track labels, perhaps we can
just check whether a label was seen so far in the current function rather than
the current compound statement, but I'm not sure how much impact that would
have on performance.
================
Comment at: lib/CodeGen/CodeGenFunction.h:236
+ LabelSeenStack.back() = true;
+ }
+
----------------
rjmccall wrote:
> A label in a nested scope acts like a label in outer scopes, too.
I think you are suggesting setting all the flags on the stack rather than just
the top (or maybe not?), but I'm not sure why that's necessary. Could you
elaborate on your comment a little more and show me a simple example when this
code would fail to disable lifetime markers when it should?
The boolean flag set to true is propagated to the outer scope's flag when we
have completed processing the compound statement and LabelSeenRAII's destructor
is called. So, for example, if I enclose label1 in function
jump_backward_over_declaration of the test case,
IRGen disables lifetime markers for "i" even though "i" is declared in the
outer compound statement of label1.
https://reviews.llvm.org/D27680
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