e2d7cd685d
This patch makes the dead_on_return parameter attribute optionally require a number
of bytes to be passed in to specify the number of bytes known to be dead
upon function return/unwind. This is aimed at enabling annotating the
this pointer in C++ destructors with dead_on_return in clang. We need
this to handle cases like the following:
```
struct X {
int n;
~X() {
this[n].n = 0;
}
};
void f() {
X xs[] = {42, -1};
}
```
Where we only certain that sizeof(X) bytes are dead upon return of ~X.
Otherwise DSE would be able to eliminate the store in ~X which would not
be correct.
This patch only does the wiring within IR. Future patches will make
clang emit correct sizing information and update DSE to only delete
stores to objects marked dead_on_return that are provably in bounds of
the number of bytes specified to be dead_on_return.
Reviewers: nikic, alinas, antoniofrighetto
Pull Request: https://github.com/llvm/llvm-project/pull/171712
27 lines
855 B
C++
27 lines
855 B
C++
// RUN: %clang_cc1 -triple armv7-apple-ios -x c++ -emit-llvm -o - %s | FileCheck %s
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// RUN: %clang_cc1 -triple arm64-apple-ios -x c++ -emit-llvm -o - %s | FileCheck %s
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// According to the Itanium ABI (3.1.1), types with non-trivial copy
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// constructors passed by value should be passed indirectly, with the caller
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// creating a temporary.
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struct Empty;
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struct Empty {
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Empty(const Empty &e);
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bool check();
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};
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bool foo(Empty e) {
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// CHECK: @_Z3foo5Empty(ptr noundef dead_on_return %e)
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// CHECK: call {{.*}} @_ZN5Empty5checkEv(ptr {{[^,]*}} %e)
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return e.check();
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}
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void caller(Empty &e) {
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// CHECK: @_Z6callerR5Empty(ptr noundef nonnull align {{[0-9]+}} dereferenceable({{[0-9]+}}) %e)
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// CHECK: call {{.*}} @_ZN5EmptyC1ERKS_(ptr {{[^,]*}} [[NEWTMP:%.*]], ptr
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// CHECK: call {{.*}} @_Z3foo5Empty(ptr noundef dead_on_return [[NEWTMP]])
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foo(e);
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}
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