From cf74881329d3b2bce063b70cbac85792a1b76b0f Mon Sep 17 00:00:00 2001
From: Lewis Revill <lewis.revill@embecosm.com>
Date: Wed, 26 Jun 2019 10:35:58 +0000
Subject: [RISCV] Add pseudo instruction for calls with explicit register

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
---
 .../RISCV/MCTargetDesc/RISCVMCCodeEmitter.cpp      | 33 ++++++++++++++--------
 1 file changed, 22 insertions(+), 11 deletions(-)

(limited to 'llvm/lib/Target/RISCV/MCTargetDesc/RISCVMCCodeEmitter.cpp')

diff --git a/llvm/lib/Target/RISCV/MCTargetDesc/RISCVMCCodeEmitter.cpp b/llvm/lib/Target/RISCV/MCTargetDesc/RISCVMCCodeEmitter.cpp
index 32e9f4e3a6c..0fc775f63ed 100644
--- a/llvm/lib/Target/RISCV/MCTargetDesc/RISCVMCCodeEmitter.cpp
+++ b/llvm/lib/Target/RISCV/MCTargetDesc/RISCVMCCodeEmitter.cpp
@@ -88,19 +88,29 @@ MCCodeEmitter *llvm::createRISCVMCCodeEmitter(const MCInstrInfo &MCII,
   return new RISCVMCCodeEmitter(Ctx, MCII);
 }
 
-// Expand PseudoCALL and PseudoTAIL to AUIPC and JALR with relocation types.
-// We expand PseudoCALL and PseudoTAIL while encoding, meaning AUIPC and JALR
-// won't go through RISCV MC to MC compressed instruction transformation. This
-// is acceptable because AUIPC has no 16-bit form and C_JALR have no immediate
-// operand field.  We let linker relaxation deal with it. When linker
-// relaxation enabled, AUIPC and JALR have chance relax to JAL. If C extension
-// is enabled, JAL has chance relax to C_JAL.
+// Expand PseudoCALL(Reg) and PseudoTAIL to AUIPC and JALR with relocation
+// types. We expand PseudoCALL(Reg) and PseudoTAIL while encoding, meaning AUIPC
+// and JALR won't go through RISCV MC to MC compressed instruction
+// transformation. This is acceptable because AUIPC has no 16-bit form and
+// C_JALR have no immediate operand field.  We let linker relaxation deal with
+// it. When linker relaxation enabled, AUIPC and JALR have chance relax to JAL.
+// If C extension is enabled, JAL has chance relax to C_JAL.
 void RISCVMCCodeEmitter::expandFunctionCall(const MCInst &MI, raw_ostream &OS,
                                             SmallVectorImpl<MCFixup> &Fixups,
                                             const MCSubtargetInfo &STI) const {
   MCInst TmpInst;
-  MCOperand Func = MI.getOperand(0);
-  unsigned Ra = (MI.getOpcode() == RISCV::PseudoTAIL) ? RISCV::X6 : RISCV::X1;
+  MCOperand Func;
+  unsigned Ra;
+  if (MI.getOpcode() == RISCV::PseudoTAIL) {
+    Func = MI.getOperand(0);
+    Ra = RISCV::X6;
+  } else if (MI.getOpcode() == RISCV::PseudoCALLReg) {
+    Func = MI.getOperand(1);
+    Ra = MI.getOperand(0).getReg();
+  } else {
+    Func = MI.getOperand(0);
+    Ra = RISCV::X1;
+  }
   uint32_t Binary;
 
   assert(Func.isExpr() && "Expected expression");
@@ -118,7 +128,7 @@ void RISCVMCCodeEmitter::expandFunctionCall(const MCInst &MI, raw_ostream &OS,
     // Emit JALR X0, X6, 0
     TmpInst = MCInstBuilder(RISCV::JALR).addReg(RISCV::X0).addReg(Ra).addImm(0);
   else
-    // Emit JALR X1, X1, 0
+    // Emit JALR Ra, Ra, 0
     TmpInst = MCInstBuilder(RISCV::JALR).addReg(Ra).addReg(Ra).addImm(0);
   Binary = getBinaryCodeForInstr(TmpInst, Fixups, STI);
   support::endian::write(OS, Binary, support::little);
@@ -169,7 +179,8 @@ void RISCVMCCodeEmitter::encodeInstruction(const MCInst &MI, raw_ostream &OS,
   // Get byte count of instruction.
   unsigned Size = Desc.getSize();
 
-  if (MI.getOpcode() == RISCV::PseudoCALL ||
+  if (MI.getOpcode() == RISCV::PseudoCALLReg ||
+      MI.getOpcode() == RISCV::PseudoCALL ||
       MI.getOpcode() == RISCV::PseudoTAIL) {
     expandFunctionCall(MI, OS, Fixups, STI);
     MCNumEmitted += 2;
-- 
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