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Summary:
Readnone attribute would cause CSE of two barriers with
the same argument, which is invalid by example:
struct Base {
virtual int foo() { return 42; }
};
struct Derived1 : Base {
int foo() override { return 50; }
};
struct Derived2 : Base {
int foo() override { return 100; }
};
void foo() {
Base *x = new Base{};
new (x) Derived1{};
int a = std::launder(x)->foo();
new (x) Derived2{};
int b = std::launder(x)->foo();
}
Here 2 calls of std::launder will produce @llvm.invariant.group.barrier,
which would be merged into one call, causing devirtualization
to devirtualize second call into Derived1::foo() instead of
Derived2::foo()
Reviewers: chandlerc, dberlin, hfinkel
Subscribers: llvm-commits, rsmith, amharc
Differential Revision: https://reviews.llvm.org/D31531
llvm-svn: 300101
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