[RISCV][GlobalISel] Select G_FRAME_INDEX (#68254)

This patch is a bandage to get G_FRAME_INDEX working. We could import
the SelectionDAG patterns for the ComplexPattern FrameAddrRegImm, and
perhaps we will do that in the future. For now we just select it as an
addition with 0.

Author: nitinjohnraj

llvm/lib/Target/RISCV/GISel/RISCVInstructionSelector.cpp

@@ -194,6 +194,14 @@ bool RISCVInstructionSelector::select(MachineInstr &MI) {
   }
   case TargetOpcode::G_SEXT_INREG:
     return selectSExtInreg(MI, MIB);
+  case TargetOpcode::G_FRAME_INDEX: {
+    // TODO: We may want to replace this code with the SelectionDAG patterns,
+    // which fail to get imported because it uses FrameAddrRegImm, which is a
+    // ComplexPattern
+    MI.setDesc(TII.get(RISCV::ADDI));
+    MI.addOperand(MachineOperand::CreateImm(0));
+    return constrainSelectedInstRegOperands(MI, TII, TRI, RBI);
+  }
   case TargetOpcode::G_SELECT:
     return selectSelect(MI, MIB, MRI);
   default:

llvm/lib/Target/RISCV/GISel/RISCVRegisterBankInfo.cpp

@@ -135,6 +135,7 @@ RISCVRegisterBankInfo::getInstrMapping(const MachineInstr &MI) const {
   case TargetOpcode::G_STORE:
     break;
   case TargetOpcode::G_CONSTANT:
+  case TargetOpcode::G_FRAME_INDEX:
   case TargetOpcode::G_GLOBAL_VALUE:
   case TargetOpcode::G_BRCOND:
     OperandsMapping = getOperandsMapping({GPRValueMapping, nullptr});

llvm/test/CodeGen/RISCV/GlobalISel/instruction-select/frame-index-rv32.mir

@@ -0,0 +1,32 @@
+# NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py
+# RUN: llc -mtriple=riscv32 -run-pass=instruction-select %s -o - \
+# RUN: | FileCheck %s
+--- |
+  define ptr @frame_index() {
+  entry:
+    %x = alloca i32, align 4
+    ret ptr %x
+  }
+
+...
+---
+name:            frame_index
+legalized:       true
+regBankSelected: true
+registers:
+  - { id: 0, class: gprb, preferred-register: '' }
+stack:
+  - { id: 0, name: x, type: default, offset: 0, size: 4, alignment: 4,
+      stack-id: default, callee-saved-register: '', callee-saved-restored: true,
+      debug-info-variable: '', debug-info-expression: '', debug-info-location: '' }
+body:             |
+  bb.1.entry:
+    ; CHECK-LABEL: name: frame_index
+    ; CHECK: [[ADDI:%[0-9]+]]:gpr = ADDI %stack.0.x, 0
+    ; CHECK-NEXT: $x10 = COPY [[ADDI]]
+    ; CHECK-NEXT: PseudoRET implicit $x10
+    %0:gprb(p0) = G_FRAME_INDEX %stack.0.x
+    $x10 = COPY %0(p0)
+    PseudoRET implicit $x10
+
+...

llvm/test/CodeGen/RISCV/GlobalISel/instruction-select/frame-index-rv64.mir

@@ -0,0 +1,32 @@
+# NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py
+# RUN: llc -mtriple=riscv64 -run-pass=instruction-select %s -o - \
+# RUN: | FileCheck %s
+--- |
+  define ptr @frame_index() {
+  entry:
+    %x = alloca i32, align 4
+    ret ptr %x
+  }
+
+...
+---
+name:            frame_index
+legalized:       true
+regBankSelected: true
+registers:
+  - { id: 0, class: gprb, preferred-register: '' }
+stack:
+  - { id: 0, name: x, type: default, offset: 0, size: 4, alignment: 4,
+      stack-id: default, callee-saved-register: '', callee-saved-restored: true,
+      debug-info-variable: '', debug-info-expression: '', debug-info-location: '' }
+body:             |
+  bb.1.entry:
+    ; CHECK-LABEL: name: frame_index
+    ; CHECK: [[ADDI:%[0-9]+]]:gpr = ADDI %stack.0.x, 0
+    ; CHECK-NEXT: $x10 = COPY [[ADDI]]
+    ; CHECK-NEXT: PseudoRET implicit $x10
+    %0:gprb(p0) = G_FRAME_INDEX %stack.0.x
+    $x10 = COPY %0(p0)
+    PseudoRET implicit $x10
+
+...

llvm/test/CodeGen/RISCV/GlobalISel/regbankselect/frame-index.mir

@@ -0,0 +1,33 @@
+# NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py
+# RUN: llc -mtriple=riscv32 -run-pass=regbankselect %s -o - \
+# RUN: | FileCheck %s
+# RUN: llc -mtriple=riscv64 -run-pass=regbankselect %s -o - \
+# RUN: | FileCheck %s
+--- |
+  define ptr @frame_index() {
+  entry:
+    %x = alloca i32, align 4
+    ret ptr %x
+  }
+
+...
+---
+name:            frame_index
+legalized:       true
+registers:
+  - { id: 0, class: _, preferred-register: '' }
+stack:
+  - { id: 0, name: x, type: default, offset: 0, size: 4, alignment: 4,
+      stack-id: default, callee-saved-register: '', callee-saved-restored: true,
+      debug-info-variable: '', debug-info-expression: '', debug-info-location: '' }
+body:             |
+  bb.1.entry:
+    ; CHECK-LABEL: name: frame_index
+    ; CHECK: [[FRAME_INDEX:%[0-9]+]]:gprb(p0) = G_FRAME_INDEX %stack.0.x
+    ; CHECK-NEXT: $x10 = COPY [[FRAME_INDEX]](p0)
+    ; CHECK-NEXT: PseudoRET implicit $x10
+    %0:_(p0) = G_FRAME_INDEX %stack.0.x
+    $x10 = COPY %0(p0)
+    PseudoRET implicit $x10
+
+...