[RISCV][VLOPT] Fix passthru check in getOperandInfo

If a pseudo has a passthru, I believe the first source operand will be the second operand, not the first.

I've added an MIR test which should show how we're reading the wrong SEW, but in order to be able to use -run-pass=riscv-vl-optimizer I needed to initialize the pass in RISCVTargetMachine.cpp.

Author: lukel97

llvm/lib/Target/RISCV/RISCVTargetMachine.cpp

@@ -128,6 +128,7 @@ extern "C" LLVM_EXTERNAL_VISIBILITY void LLVMInitializeRISCVTarget() {
   initializeRISCVPreRAExpandPseudoPass(*PR);
   initializeRISCVExpandPseudoPass(*PR);
   initializeRISCVVectorPeepholePass(*PR);
+  initializeRISCVVLOptimizerPass(*PR);
   initializeRISCVInsertVSETVLIPass(*PR);
   initializeRISCVInsertReadWriteCSRPass(*PR);
   initializeRISCVInsertWriteVXRMPass(*PR);

llvm/lib/Target/RISCV/RISCVVLOptimizer.cpp

@@ -431,7 +431,7 @@ static OperandInfo getOperandInfo(const MachineInstr &MI,
   case RISCV::VWMACCSU_VV:
   case RISCV::VWMACCSU_VX:
   case RISCV::VWMACCUS_VX: {
-    bool IsOp1 = HasPassthru ? MO.getOperandNo() == 1 : MO.getOperandNo() == 2;
+    bool IsOp1 = HasPassthru ? MO.getOperandNo() == 2 : MO.getOperandNo() == 1;
     bool TwoTimes = IsMODef || IsOp1;
     unsigned Log2EEW = TwoTimes ? MILog2SEW + 1 : MILog2SEW;
     RISCVII::VLMUL EMUL =
@@ -467,7 +467,7 @@ static OperandInfo getOperandInfo(const MachineInstr &MI,
   case RISCV::VNCLIP_WI:
   case RISCV::VNCLIP_WV:
   case RISCV::VNCLIP_WX: {
-    bool IsOp1 = HasPassthru ? MO.getOperandNo() == 1 : MO.getOperandNo() == 2;
+    bool IsOp1 = HasPassthru ? MO.getOperandNo() == 2 : MO.getOperandNo() == 1;
     bool TwoTimes = IsOp1;
     unsigned Log2EEW = TwoTimes ? MILog2SEW + 1 : MILog2SEW;
     RISCVII::VLMUL EMUL =

llvm/test/CodeGen/RISCV/rvv/vl-opt.mir

@@ -10,7 +10,7 @@ body: |
     ; CHECK: liveins: $x1
     ; CHECK-NEXT: {{  $}}
     ; CHECK-NEXT: %vl:gprnox0 = COPY $x1
-    ; CHECK-NEXT: %x:vr = PseudoVADD_VV_MF4 $noreg, $noreg, $noreg, %vl, 4 /* e16 */, 0 /* tu, mu */
+    ; CHECK-NEXT: %x:vr = PseudoVADD_VV_MF4 $noreg, $noreg, $noreg, -1, 4 /* e16 */, 0 /* tu, mu */
     ; CHECK-NEXT: %y:vr = PseudoVNSRL_WV_MF4 $noreg, %x, $noreg, %vl, 4 /* e16 */, 0 /* tu, mu */
     %vl:gprnox0 = COPY $x1
     %x:vr = PseudoVADD_VV_MF4 $noreg, $noreg, $noreg, -1, 4 /* e16 */, 0 /* tu, mu */