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This patch adds infrastructure support for passing array types directly. These can be used by the front-end to pass aggregate types (coerced to an appropriate array type). The details of the array type being used inform the back-end about ABI-relevant properties. Specifically, the array element type encodes: - whether the parameter should be passed in FPRs, VRs, or just GPRs/stack slots (for float / vector / integer element types, respectively) - what the alignment requirements of the parameter are when passed in GPRs/stack slots (8 for float / 16 for vector / the element type size for integer element types) -- this corresponds to the "byval align" field Using the infrastructure provided by this patch, a companion patch to clang will enable two features: - In the ELFv2 ABI, pass (and return) "homogeneous" floating-point or vector aggregates in FPRs and VRs (this is similar to the ARM homogeneous aggregate ABI) - As an optimization for both ELFv1 and ELFv2 ABIs, pass aggregates that fit fully in registers without using the "byval" mechanism The patch uses the functionArgumentNeedsConsecutiveRegisters callback to encode that special treatment is required for all directly-passed array types. The isInConsecutiveRegs / isInConsecutiveRegsLast bits set as a results are then used to implement the required size and alignment rules in CalculateStackSlotSize / CalculateStackSlotAlignment etc. As a related change, the ABI routines have to be modified to support passing floating-point types in GPRs. This is necessary because with homogeneous aggregates of 4-byte float type we can now run out of FPRs *before* we run out of the 64-byte argument save area that is shadowed by GPRs. Any extra floating-point arguments that no longer fit in FPRs must now be passed in GPRs until we run out of those too. Note that there was already code to pass floating-point arguments in GPRs used with vararg parameters, which was done by writing the argument out to the argument save area first and then reloading into GPRs. The patch re-implements this, however, in favor of code packing float arguments directly via extension/truncation, BITCAST, and BUILD_PAIR operations. This is required to support the ELFv2 ABI, since we cannot unconditionally write to the argument save area (which the caller might not have allocated). The change does, however, affect ELFv1 varags routines too; but even here the overall effect should be advantageous: Instead of loading the argument into the FPR, then storing the argument to the stack slot, and finally reloading the argument from the stack slot into a GPR, the new code now just loads the argument into the FPR, and subsequently loads the argument into the GPR (via BITCAST). That BITCAST might imply a save/reload from a stack temporary (in which case we're no worse than before); but it might be implemented more efficiently in some cases. The final part of the patch enables up to 8 FPRs and VRs for argument return in PPCCallingConv.td; this is required to support returning ELFv2 homogeneous aggregates. (Note that this doesn't affect other ABIs since LLVM wil only look for which register to use if the parameter is marked as "direct" return anyway.) Reviewed by Hal Finkel. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@213493 91177308-0d34-0410-b5e6-96231b3b80d8 |
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