hubert.reinterpretcast added inline comments.
================
Comment at: clang/test/Layout/aix-double-struct-member.cpp:1
+// RUN: %clang_cc1 -emit-llvm-only -triple powerpc-ibm-aix-xcoff \
+// RUN: -fdump-record-layouts -fsyntax-only %s 2>/dev/null | \
----------------
Xiangling_L wrote:
> hubert.reinterpretcast wrote:
> > I am concerned that none of the tests actually create an instance of the
> > classes under test and check the alignment (or related adjustments) in the
> > IR. That is, we set up the preferred alignment value but don't check that
> > we use it where we should.
> >
> > As it is, it seems array new/delete has problems:
> > ```
> > #include <assert.h>
> > extern "C" void *calloc(decltype(sizeof 0), decltype(sizeof 0));
> > extern "C" void free(void *);
> > extern "C" int printf(const char *, ...);
> >
> > extern void *allocated_ptr;
> > extern decltype(sizeof 0) allocated_size;
> > struct B {
> > double d;
> > ~B() {}
> > static void *operator new[](decltype(sizeof 0) sz);
> > static void operator delete[](void *p, decltype(sizeof 0) sz);
> > };
> > B *allocBp();
> >
> > #ifdef ALLOCBP
> > void *allocated_ptr;
> > decltype(sizeof 0) allocated_size;
> > void *B::operator new[](decltype(sizeof 0) sz) {
> > void *alloc = calloc(1u, allocated_size = sz);
> > printf("%p: %s\n", alloc, __PRETTY_FUNCTION__);
> > printf("%zu\n", sz);
> > return allocated_ptr = alloc;
> > }
> > void B::operator delete[](void *p, decltype(sizeof 0) sz) {
> > printf("%p: %s\n", p, __PRETTY_FUNCTION__);
> > printf("%zu\n", sz);
> > assert(sz == allocated_size);
> > assert(p == allocated_ptr);
> > free(p);
> > }
> > B *allocBp() { return new B[2]; }
> > #endif
> >
> > #ifdef MAIN
> > int main(void) { delete[] allocBp(); }
> > #endif
> > ```
> >
> > The `xlclang++` invocation from XL C/C++ generates padding before the
> > 32-bit `new[]` cookie. I'm not seeing that padding with this patch.
> Thank. I will create more practical testcases as you mentioned in your
> concern. And regarding to `padding before the 32-bit new[] cookie` issue, I
> am wondering is that part of `power` alignment rule or what rules do we
> follow to generate this kind of padding?
The padding has to do with the alignment. The allocation function returns
8-byte aligned memory. The 32-bit cookie takes 4 of the first 8 bytes. The
type's preferred alignment is 8, so there are 4 bytes of padding.
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D79719/new/
https://reviews.llvm.org/D79719
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