In addition to enabling ELFv2 homogeneous aggregate handling,
LLVM support to pass array types directly also enables a performance
enhancement. We can now pass (non-homogeneous) aggregates that fit
fully in registers as direct integer arrays, using an element type
to encode the alignment requirement (that would otherwise go to the
"byval align" field).
This is preferable since "byval" forces the back-end to write the
aggregate out to the stack, even if it could be passed fully in
registers. This is particularly annoying on ELFv2, if there is
no parameter save area available, since we then need to allocate
space on the callee's stack just to hold those aggregates.
Note that to implement this optimization, this patch does not attempt
to fully anticipate register allocation rules as (defined in the
ABI and) implemented in the back-end. Instead, the patch is simply
passing *any* aggregate passed by value using the array mechanism
if its size is up to 64 bytes. This means that some of those will
end up being passed in stack slots anyway, but the generated code
shouldn't be any worse either. (*Large* aggregates remain passed
using "byval" to enable optimized copying via memcpy etc.)
llvm-svn: 213495
This patch adds support for respecting the ABI and type alignment
of aggregates passed by value. Currently, all aggregates are aligned
at 8 bytes in the parameter save area. This is incorrect for two
reasons:
- Aggregates that need alignment of 16 bytes or more should be aligned
at 16 bytes in the parameter save area. This is implemented by
using an appropriate "byval align" attribute in the IR.
- Aggregates that need alignment beyond 16 bytes need to be dynamically
realigned by the caller. This is implemented by setting the Realign
flag of the ABIArgInfo::getIndirect call.
In addition, when expanding a va_arg call accessing a type that is
aligned at 16 bytes in the argument save area (either one of the
aggregate types as above, or a vector type which is already aligned
at 16 bytes), code needs to align the va_list pointer accordingly.
Reviewed by Hal Finkel.
llvm-svn: 212743
This patch adds support for passing arguments of non-Altivec vector type
(i.e. defined via attribute ((vector_size (...)))) on powerpc64-linux.
While such types are not mentioned in the formal ABI document, this
patch implements a calling convention compatible with GCC:
- Vectors of size < 16 bytes are passed in a GPR
- Vectors of size > 16 bytes are passed via reference
Note that vector types with a number of elements that is not a power
of 2 are not supported by GCC, so there is no pre-existing ABI to
follow. We choose to pass those (of size < 16) as if widened to the
next power of two, so they might end up in a vector register or
in a GPR. (Sizes > 16 are always passed via reference as well.)
Reviewed by Hal Finkel.
llvm-svn: 212734
Ulrich Weigand