[CHERIoT] Pass two-caps return values and arguments in registers #178
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clang/lib/CodeGen/Targets/RISCV.cpp
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| if (auto *RT = Ty->getAs<RecordType>()) { | ||
| unsigned MaxCapRegs = IsCheriot ? 2 : 1; | ||
| return Size == MaxCapRegs * getTarget().getCHERICapabilityWidth() && |
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Should this be <= rather than ==?
clang/lib/CodeGen/Targets/RISCV.cpp
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| bool IsCapability = Ty->isCHERICapabilityType(getContext()) || | ||
| IsSingleCapRecord; | ||
| (ForcePassInCapRegs && Size == CapabilityWidth); |
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This could be just ForcePassInCapRegs if you change == to <= in shouldPassStructDirectInCapRegisters
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Per chat discussion, if we can't simplify the logic, perhaps we can rename the variables to make the logic simpler?
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Here's the relevant bit of the discussion: the final goal is that of having IsCapability true iff. the type is itself a capability or a struct made of a single capability, the case where the struct is composed of >= 2 capabilities should not entail IsCapability == true.
Latest commit renames IsCapability to IsSingleCapability!
clang/lib/CodeGen/Targets/RISCV.cpp
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| bool IsCapability = Ty->isCHERICapabilityType(getContext()) || | ||
| IsSingleCapRecord; | ||
| (ForcePassInCapRegs && Size == CapabilityWidth); |
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The previous code was not taking into account the case for |
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resistor
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This is way better than before!
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| /// CHERI(oT)-specific: Figure out how many registers are needed to pass a | ||
| /// value of the given type and size directly in register(s). The value of | ||
| /// `-1` means that the value should be passed indirectly. |
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Can't 0 be the sentinel?
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I set it to -1 because I am not completely sure about the semantics of zero-sized types and, perhaps, there might be a situation where we want to know that the value "fits in 0 registers", if that makes any sense.
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Should close #177. This PR also adds the same mechanism for arguments that can be subjected to the same optimisation.