[llvm] [GlobalISel] Add G_STEP_VECTOR instruction (PR #115598)

[Thorsten Schütt via llvm-commits]

================
@@ -1729,6 +1729,36 @@ void MachineVerifier::verifyPreISelGenericInstruction(const MachineInstr *MI) {
     }
     break;
   }
+  case TargetOpcode::G_STEP_VECTOR: {
+    if (!MI->getOperand(1).isCImm()) {
+      report("operand must be cimm", MI);
+      break;
+    }
+
+    if (!MI->getOperand(1).getCImm()->getValue().isStrictlyPositive()) {
+      report("step must be >= 0", MI);
+      break;
+    }
----------------
tschuett wrote:

For step=0, we create a step vector of all zeros. The canonical representation is a splat vector of zeros. It would loose the stepping property.

https://github.com/llvm/llvm-project/pull/115598