r246877 made __builtin_object_size substantially more aggressive with
unknown bases if Type=1 or Type=3, which causes issues when we encounter
code like this:
struct Foo {
int a;
char str[1];
};
const char str[] = "Hello, World!";
struct Foo *f = (struct Foo *)malloc(sizeof(*f) + strlen(str));
strcpy(&f->str, str);
__builtin_object_size(&f->str, 1) would hand back 1, which is
technically correct given the type of Foo, but the type of Foo lies to
us about how many bytes are available in this case.
This patch adds support for this "writing off the end" idiom -- we now
answer conservatively when we're given the address of the very last
member in a struct.
Differential Revision: http://reviews.llvm.org/D12169
llvm-svn: 250488
Introduce an Address type to bundle a pointer value with an
alignment. Introduce APIs on CGBuilderTy to work with Address
values. Change core APIs on CGF/CGM to traffic in Address where
appropriate. Require alignments to be non-zero. Update a ton
of code to compute and propagate alignment information.
As part of this, I've promoted CGBuiltin's EmitPointerWithAlignment
helper function to CGF and made use of it in a number of places in
the expression emitter.
The end result is that we should now be significantly more correct
when performing operations on objects that are locally known to
be under-aligned. Since alignment is not reliably tracked in the
type system, there are inherent limits to this, but at least we
are no longer confused by standard operations like derived-to-base
conversions and array-to-pointer decay. I've also fixed a large
number of bugs where we were applying the complete-object alignment
to a pointer instead of the non-virtual alignment, although most of
these were hidden by the very conservative approach we took with
member alignment.
Also, because IRGen now reliably asserts on zero alignments, we
should no longer be subject to an absurd but frustrating recurring
bug where an incomplete type would report a zero alignment and then
we'd naively do a alignmentAtOffset on it and emit code using an
alignment equal to the largest power-of-two factor of the offset.
We should also now be emitting much more aggressive alignment
attributes in the presence of over-alignment. In particular,
field access now uses alignmentAtOffset instead of min.
Several times in this patch, I had to change the existing
code-generation pattern in order to more effectively use
the Address APIs. For the most part, this seems to be a strict
improvement, like doing pointer arithmetic with GEPs instead of
ptrtoint. That said, I've tried very hard to not change semantics,
but it is likely that I've failed in a few places, for which I
apologize.
ABIArgInfo now always carries the assumed alignment of indirect and
indirect byval arguments. In order to cut down on what was already
a dauntingly large patch, I changed the code to never set align
attributes in the IR on non-byval indirect arguments. That is,
we still generate code which assumes that indirect arguments have
the given alignment, but we don't express this information to the
backend except where it's semantically required (i.e. on byvals).
This is likely a minor regression for those targets that did provide
this information, but it'll be trivial to add it back in a later
patch.
I partially punted on applying this work to CGBuiltin. Please
do not add more uses of the CreateDefaultAligned{Load,Store}
APIs; they will be going away eventually.
llvm-svn: 246985
Improvements:
- For all types, we would give up in a case such as:
__builtin_object_size((char*)&foo, N);
even if we could provide an answer to
__builtin_object_size(&foo, N);
We now provide the same answer for both of the above examples in all
cases.
- For type=1|3, we now support subobjects with unknown bases, as long
as the designator is valid.
Thanks to Richard Smith for the review + design planning.
Review: http://reviews.llvm.org/D12169
llvm-svn: 246877
__builtin_object_size would return incorrect answers for many uses where
type=3. This fixes the inaccuracy by making us emit 0 instead of LLVM's
objectsize intrinsic.
Additionally, there are many cases where we would emit suboptimal (but
correct) answers, such as when arrays are involved. This patch fixes
some of these cases (please see new tests in test/CodeGen/object-size.c
for specifics on which cases are improved)
Resubmit of r245323 with PR24493 fixed.
Patch mostly by Richard Smith.
Differential Revision: http://reviews.llvm.org/D12000
This fixes PR15212.
llvm-svn: 245403
__builtin_object_size would return incorrect answers for many uses where
type=3. This fixes the inaccuracy by making us emit 0 instead of LLVM's
objectsize intrinsic.
Additionally, there are many cases where we would emit suboptimal (but
correct) answers, such as when arrays are involved. This patch fixes
some of these cases (please see new tests in test/CodeGen/object-size.c
for specifics on which cases are improved)
Patch mostly by Richard Smith.
Differential Revision: http://reviews.llvm.org/D12000
This fixes PR15212.
llvm-svn: 245323
pointer, but such folding encounters side-effects, ignore the side-effects
rather than performing them at runtime: CodeGen generates wrong code for
__builtin_object_size in that case.
llvm-svn: 157310
would trigger an extra method call).
- While in the area, I also changed Clang to not emit an unnecessary load from
'x' in cases like 'y = (x = 1)'.
llvm-svn: 107210
only takes a boolean second argument now. Update tests accordingly.
Currently the builtin still accepts the full range for compatibility.
llvm-svn: 91983
- This is designed to make it obvious that %clang_cc1 is a "test variable"
which is substituted. It is '%clang_cc1' instead of '%clang -cc1' because it
can be useful to redefine what gets run as 'clang -cc1' (for example, to set
a default target).
llvm-svn: 91446
Bob Wilson