This patch adds the PseudoCALLReg instruction which allows using an
explicit register operand as the destination for the return address.
GCC can successfully parse this form of the call instruction, which
would be used for calls to functions which do not use ra as the return
address register, such as the __riscv_save libcalls. This patch forms
the first part of an implementation of -msave-restore for RISC-V.
Differential Revision: https://reviews.llvm.org/D62685
llvm-svn: 364403
To do this:
1. Add PseudoCALLIndirct to match indirect function call.
2. Add PseudoCALL to support parsing and print pseudo `call` in assembly
3. Expand PseudoCALL to the following form with R_RISCV_CALL relocation type
while encoding:
auipc ra, func
jalr ra, ra, 0
If we expand PseudoCALL before emitting assembly, we will see auipc and jalr
pair when compile with -S. It's hard for assembly parser to parsing this
pair and identify it's semantic is function call and then insert R_RISCV_CALL
relocation type. Although we could insert R_RISCV_PCREL_HI20 and
R_RISCV_PCREL_LO12_I relocation types instead of R_RISCV_CALL.
Due to RISCV relocation design, auipc and jalr pair only can relax to jal with
R_RISCV_CALL + R_RISCV_RELAX relocation types.
We expand PseudoCALL as late as encoding(RISCVMCCodeEmitter) instead of before
emitting assembly(RISCVAsmPrinter) because we want to preserve call
pseudoinstruction in assembly code. It's more readable and assembly parser
could identify call assembly and insert R_RISCV_CALL relocation type.
Differential Revision: https://reviews.llvm.org/D45859
llvm-svn: 330826
Lewis Revill