AMDGPU: Verify that SOP2/SOPC instructions have at most one immediate operand

[nhaehnle]

Summary

No test case because I don't know of a way to trigger this, but I
accidentally caused this to fail while working on a different change.

Change-Id: I8015aa447fe27163cc4e4902205a203bd44bf7e3

[arsenm]

You can write a pure verifier test

[rampitec]

LGTM

[nhaehnle]

Added a minimal verifier-only test before commit.

lib/Target/AMDGPU/SIInstrInfo.cpp

if (Src0.isReg() && Src1.isReg() && Src2.isReg()) {
       if (!compareMachineOp(Src0, Src1) &&
           !compareMachineOp(Src0, Src2)) {
         ErrInfo = "v_div_scale_{f32|f64} require src0 = src1 or src2";
         return false;
       }
     }
   }
 
+  if (isSOP2(MI) || isSOPC(MI)) {
+    const MachineOperand &Src0 = MI.getOperand(Src0Idx);
+    const MachineOperand &Src1 = MI.getOperand(Src1Idx);
+    unsigned Immediates = 0;
+
+    if (!Src0.isReg() &&
+        !isInlineConstant(Src0, Desc.OpInfo[Src0Idx].OperandType))
+      Immediates++;
+    if (!Src1.isReg() &&
+        !isInlineConstant(Src1, Desc.OpInfo[Src1Idx].OperandType))
+      Immediates++;
+
+    if (Immediates > 1) {
+      ErrInfo = "SOP2/SOPC instruction requires too many immediate constants";
+      return false;
+    }
+  }
+
   if (isSOPK(MI)) {
     int64_t Imm = getNamedOperand(MI, AMDGPU::OpName::simm16)->getImm();
     if (sopkIsZext(MI)) {
       if (!isUInt<16>(Imm)) {
         ErrInfo = "invalid immediate for SOPK instruction";
         return false;
       }
     } else {