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Although PNaCl doesn't fully support struct types as varargs
arguments, there is a test in Spec2k (255.vortex) that passes a struct
as a varargs argument but never reads the argument using va_arg (which
is legal, but strange).
ExpandVarArgs was handling the struct argument by copying it with a
struct load+store. This is undesirable because currently SROA
converts that into code that uses extractvalue, which was rejected by
the PNaCl ABI checker. Struct load/store will soon be rejected by the
ABI checker too.
We could fix this by running ExpandStructRegs after ExpandVarArgs, but
it's cleaner for ExpandVarArgs to use memcpy() instead of struct
load+store. memcpy() is potentially more efficient because it avoids
having a temporary copy of the struct, and using memcpy() avoids
dependencies between IR passes.
BUG=https://code.google.com/p/nativeclient/issues/detail?id=3338
BUG=https://code.google.com/p/nativeclient/issues/detail?id=3343
TEST=*.ll tests + built 255.vortex from Spec2k
Review URL: https://codereview.chromium.org/16232021
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Saves a tiny bit of space for var-args heavy bitcode
programs, since the anonymous types get unique'ed. E.g.,
saves 20KB out of 1.6MB in spec gcc when comparing the
gzipped files, or about 100KB when not zipped. This is only
a savings with the current wire format. If we change the
alloca, etc. to only have sizes and not struct types
then we would also not have this duplication.
Just happened to notice while looking through code for
what struct types remain used in the bitcode.
random cleanup for:
BUG= https://code.google.com/p/nativeclient/issues/detail?id=3338
R=mseaborn@chromium.org
Review URL: https://codereview.chromium.org/14197004
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* Ensure that the "byval" attribute is preserved for the fixed
arguments. Before, it was stripped off from function calls but
left in for function definitions, which broke passing struct
arguments (which PNaCl Clang generates as "byval").
* Ensure that function and return attributes are preserved too.
* Handle "byval" variable arguments in calls too by dereferencing the
pointer. These are not yet usable with PNaCl Clang, which does not
allow va_arg on structs (see
https://code.google.com/p/nativeclient/issues/detail?id=2381), but
we might as well make this pass ready to handle this.
BUG=https://code.google.com/p/nativeclient/issues/detail?id=3338
TEST=test/Transforms/NaCl/expand-varargs*.ll
Review URL: https://codereview.chromium.org/13100002
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