[GISel] Fix crash in GlobalISel utils method (#153334)

The `getDefSrcRegIgnoringCopies` method in GlobalISel Utils crashed when
the first operand of the input instruction was not a register, e.g.,
the `INLINEASM` instruction has a non-register first operand.

---------

Co-authored-by: Matt Arsenault <[email protected]>

Author: vmustya

llvm/lib/CodeGen/GlobalISel/Utils.cpp

@@ -466,8 +466,14 @@ llvm::getConstantFPVRegVal(Register VReg, const MachineRegisterInfo &MRI) {
 std::optional<DefinitionAndSourceRegister>
 llvm::getDefSrcRegIgnoringCopies(Register Reg, const MachineRegisterInfo &MRI) {
   Register DefSrcReg = Reg;
-  auto *DefMI = MRI.getVRegDef(Reg);
-  auto DstTy = MRI.getType(DefMI->getOperand(0).getReg());
+  // This assumes that the code is in SSA form, so there should only be one
+  // definition.
+  auto DefIt = MRI.def_begin(Reg);
+  if (DefIt == MRI.def_end())
+    return {};
+  MachineOperand &DefOpnd = *DefIt;
+  MachineInstr *DefMI = DefOpnd.getParent();
+  auto DstTy = MRI.getType(DefOpnd.getReg());
   if (!DstTy.isValid())
     return std::nullopt;
   unsigned Opc = DefMI->getOpcode();

llvm/test/CodeGen/AMDGPU/GlobalISel/regbankcombiner-ignore-copies-crash.mir

@@ -0,0 +1,77 @@
+# NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py UTC_ARGS: --version 5
+# RUN: llc -mtriple=amdgcn-amd-mesa3d -mcpu=gfx1200 -run-pass=amdgpu-regbank-combiner %s -o - | FileCheck %s
+
+# COM: Check that the pass doesn't crash.
+
+---
+name: test_inline_asm
+legalized: true
+regBankSelected: true
+tracksRegLiveness: true
+machineFunctionInfo:
+  mode:
+    ieee: true
+    dx10-clamp: true
+body: |
+  bb.1 :
+    liveins: $vgpr0
+
+    ; CHECK-LABEL: name: test_inline_asm
+    ; CHECK: liveins: $vgpr0
+    ; CHECK-NEXT: {{  $}}
+    ; CHECK-NEXT: [[COPY:%[0-9]+]]:vgpr(s32) = COPY $vgpr0
+    ; CHECK-NEXT: [[C:%[0-9]+]]:sgpr(s32) = G_FCONSTANT float 2.000000e+00
+    ; CHECK-NEXT: [[COPY1:%[0-9]+]]:vgpr(s32) = COPY [[C]](s32)
+    ; CHECK-NEXT: [[FMUL:%[0-9]+]]:vgpr(s32) = G_FMUL [[COPY]], [[COPY1]]
+    ; CHECK-NEXT: [[C1:%[0-9]+]]:sgpr(s32) = G_FCONSTANT float 1.000000e+00
+    ; CHECK-NEXT: INLINEASM &"v_mov_b32 $0, 0", 0 /* attdialect */, 2228234 /* regdef:VGPR_32 */, def %5(s32)
+    ; CHECK-NEXT: [[COPY2:%[0-9]+]]:vgpr(s32) = COPY [[C1]](s32)
+    ; CHECK-NEXT: [[AMDGPU_FMED3_:%[0-9]+]]:vgpr(s32) = nnan G_AMDGPU_FMED3 [[FMUL]], %5, [[COPY2]]
+    ; CHECK-NEXT: $vgpr0 = COPY [[AMDGPU_FMED3_]](s32)
+    %0:vgpr(s32) = COPY $vgpr0
+    %1:sgpr(s32) = G_FCONSTANT float 2.000000e+00
+    %2:vgpr(s32) = COPY %1(s32)
+    %3:vgpr(s32) = G_FMUL %0, %2
+    %4:sgpr(s32) = G_FCONSTANT float 1.000000e+00
+    INLINEASM &"v_mov_b32 $0, 0", 0 /* attdialect */, 2228234 /* regdef:VGPR_32 */, def %5:vgpr_32
+    %6:vgpr(s32) = COPY %4(s32)
+    %7:vgpr(s32) = nnan G_AMDGPU_FMED3 %3(s32), %5(s32), %6(s32)
+    $vgpr0 = COPY %7(s32)
+...
+
+---
+name: test_unmerge_values
+legalized: true
+regBankSelected: true
+tracksRegLiveness: true
+machineFunctionInfo:
+  mode:
+    ieee: true
+    dx10-clamp: true
+body: |
+  bb.1 :
+    liveins: $vgpr0
+
+    ; CHECK-LABEL: name: test_unmerge_values
+    ; CHECK: liveins: $vgpr0
+    ; CHECK-NEXT: {{  $}}
+    ; CHECK-NEXT: [[COPY:%[0-9]+]]:vgpr(s32) = COPY $vgpr0
+    ; CHECK-NEXT: [[C:%[0-9]+]]:sgpr(s32) = G_FCONSTANT float 2.000000e+00
+    ; CHECK-NEXT: [[COPY1:%[0-9]+]]:vgpr(s32) = COPY [[C]](s32)
+    ; CHECK-NEXT: [[FMUL:%[0-9]+]]:vgpr(s32) = G_FMUL [[COPY]], [[COPY1]]
+    ; CHECK-NEXT: [[C1:%[0-9]+]]:sgpr(s32) = G_FCONSTANT float 1.000000e+00
+    ; CHECK-NEXT: [[C2:%[0-9]+]]:vgpr(s32) = G_CONSTANT i32 0
+    ; CHECK-NEXT: [[COPY2:%[0-9]+]]:vgpr(s32) = COPY [[C1]](s32)
+    ; CHECK-NEXT: [[AMDGPU_FMED3_:%[0-9]+]]:vgpr(s32) = nnan G_AMDGPU_FMED3 [[FMUL]], [[C2]], [[COPY2]]
+    ; CHECK-NEXT: $vgpr0 = COPY [[C2]](s32)
+    %0:vgpr(s32) = COPY $vgpr0
+    %1:sgpr(s32) = G_FCONSTANT float 2.000000e+00
+    %2:vgpr(s32) = COPY %1(s32)
+    %3:vgpr(s32) = G_FMUL %0, %2
+    %4:sgpr(s32) = G_FCONSTANT float 1.000000e+00
+    %5:vgpr(s64) = G_CONSTANT i64 123456789
+    %6:vgpr(s32), %7:vgpr(s32) = G_UNMERGE_VALUES %5(s64)
+    %8:vgpr(s32) = COPY %4(s32)
+    %9:vgpr(s32) = nnan G_AMDGPU_FMED3 %3(s32), %7(s32), %8(s32)
+    $vgpr0 = COPY %7(s32)
+...