[RISCV][GlobalISel] Select G_GLOBAL_VALUE for medlow code model

[nitinjohnraj]

We create generic instructions to serve as globalisel equivalents to selection DAG nodes, in order to leverage the SelectionDAG patterns. We lower G_GLOBAL_VALUE to these generic instructions.

[nitinjohnraj]

Currently, this patch does not compile. I'm trying to figure out which file to import in order to use the new generic instruction opcodes in the instruction selector. Also, I'm only trying to handle the medlow code model for now. I intend to add code for medany as well.

[github-actions]

⚠️ C/C++ code formatter, clang-format found issues in your code. ⚠️

You can test this locally with the following command:

git-clang-format --diff ce8ed0008713781e58777d251f654a9a547f43b7 b1f7484e6ca571121ffeffd28316b48e6befb59c -- llvm/lib/Target/RISCV/GISel/RISCVInstructionSelector.cpp

View the diff from clang-format here.

diff --git a/llvm/lib/Target/RISCV/GISel/RISCVInstructionSelector.cpp b/llvm/lib/Target/RISCV/GISel/RISCVInstructionSelector.cpp
index a63e9d111d9d..650b186a5626 100644
--- a/llvm/lib/Target/RISCV/GISel/RISCVInstructionSelector.cpp
+++ b/llvm/lib/Target/RISCV/GISel/RISCVInstructionSelector.cpp
@@ -359,8 +359,8 @@ bool RISCVInstructionSelector::selectConstant(MachineInstr &MI,
   return true;
 }
 
-bool RISCVInstructionSelector::selectGlobalValue(MachineInstr &MI, MachineIRBuilder &MIB,
-                                                 MachineRegisterInfo &MRI) const {
+bool RISCVInstructionSelector::selectGlobalValue(
+    MachineInstr &MI, MachineIRBuilder &MIB, MachineRegisterInfo &MRI) const {
   assert(MI.getOpcode() == TargetOpcode::G_GLOBAL_VALUE &&
          "Wrong selector used!");
 
@@ -369,14 +369,15 @@ bool RISCVInstructionSelector::selectGlobalValue(MachineInstr &MI, MachineIRBuil
     Register DstReg = MI.getOperand(0).getReg();
     const GlobalValue *GV = MI.getOperand(1).getGlobal();
     Register TmpReg = MRI.createVirtualRegister(&RISCV::GPRRegClass);
-    MachineInstr *Result =
-        MIB.buildInstr(RISCV::LUI).addDef(TmpReg).addGlobalAddress(GV, 0, RISCVII::MO_HI);
+    MachineInstr *Result = MIB.buildInstr(RISCV::LUI)
+                               .addDef(TmpReg)
+                               .addGlobalAddress(GV, 0, RISCVII::MO_HI);
 
     if (!constrainSelectedInstRegOperands(*Result, TII, TRI, RBI))
       return false;
 
     Result = MIB.buildInstr(RISCV::ADDI)
-      .addDef(DstReg)
+                 .addDef(DstReg)
                  .addReg(TmpReg)
                  .addGlobalAddress(GV, 0, RISCVII::MO_LO);
 

[arsenm]

G_RISCV_?

[nitinjohnraj]

I abandoned using these generic instructions. If you look at the next comment, you'll see they were deleted; I didn't squash the comment so that I could preserve that version in case we decided to revert to that.

In the future, would it be better if I squashed such changed?

[nitinjohnraj]

If we decide to go with the generic instruction approach, I will rename them accordingly, though, it does make things much clearer.

[michaelmaitland]

I abandoned using these generic instructions

These look to be part of the overall diff still. Do you plan on removing the changes in this file if you are not going to use them?

[michaelmaitland]

This function needs to be clang-format'ed

[arsenm]

Requires resolve to main