[RISCV] Support -target-abi at the MC layer and for codegen

This patch adds proper handling of -target-abi, as accepted by llvm-mc and
llc. Lowering (codegen) for the hard-float ABIs will follow in a subsequent
patch. However, this patch does add MC layer support for the hard float and
RVE ABIs (emission of the appropriate ELF flags
https://github.com/riscv/riscv-elf-psabi-doc/blob/master/riscv-elf.md#-file-header).

ABI parsing must be shared between codegen and the MC layer, so we add
computeTargetABI to RISCVUtils. A warning will be printed if an invalid or
unrecognized ABI is given.

Differential Revision: https://reviews.llvm.org/D59023

llvm-svn: 355771

1 files changed, 6 insertions, 0 deletions

diff --git a/llvm/lib/Target/RISCV/RISCVISelLowering.cpp b/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
index f46a21a9bff..d844a8364eb 100644
--- a/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
+++ b/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
@@ -42,6 +42,12 @@ RISCVTargetLowering::RISCVTargetLowering(const TargetMachine &TM,
                                          const RISCVSubtarget &STI)
     : TargetLowering(TM), Subtarget(STI) {
 
+  RISCVABI::ABI ABI = Subtarget.getTargetABI();
+  assert(ABI != RISCVABI::ABI_Unknown && "Improperly initialised target ABI");
+
+  if (ABI != RISCVABI::ABI_ILP32 && ABI != RISCVABI::ABI_LP64)
+    report_fatal_error("Don't know how to lower this ABI");
+
   MVT XLenVT = Subtarget.getXLenVT();
 
   // Set up the register classes.