This patch implements the caller side of placing function call arguments
in stack memory. This removes the current limitation where LLVM on AIX
will report fatal error when arguments can't be contained in registers.
There is a particular oddity that a float argument that passes in a
register and also in stack memory requires that the caller initialize
both. From what AIX "ABI" documentation I have it's not clear that this
needs to be done, however, it is necessary for compatibility with the
AIX XL compiler so I think it's best to implement it the same way.
Note a later patch will follow to address the callee side.
Differential Revision: https://reviews.llvm.org/D73209
Summary:
This patch pushes the AIX vararg unimplemented error diagnostic later
and allows vararg calls so long as all the arguments can be passed in register.
This patch extends the AIX calling convention implementation to initialize
GPR(s) for vararg float arguments. On AIX, both GPR(s) and FPR are allocated
for floating point arguments. The GPR(s) are only initialized for vararg calls,
otherwise the callee is expected to retrieve the float argument in the FPR.
f64 in AIX PPC32 requires special handling in order to allocated and
initialize 2 GPRs. This is performed with bitcast, SRL, truncation to
initialize one GPR for the MSW and bitcast, truncations to initialize
the other GPR for the LSW.
A future patch will follow to add support for arguments passed on the stack.
Patch provided by: cebowleratibm
Reviewers: sfertile, ZarkoCA, hubert.reinterpretcast
Differential Revision: https://reviews.llvm.org/D71013
Chris Bowler