[mlir][spirv] Add tests for scf.while and scf.for in convert-to-spirv pass (#102528)

This PR adds lit tests that check for `scf.while` and `scf.for`
conversions for the `convert-to-spirv` pass, introduced in #95942.

Author: angelz913

mlir/test/Conversion/ConvertToSPIRV/scf.mlir

@@ -33,6 +33,16 @@ func.func @if_yield(%arg0: i1) -> f32 {
 }
 
 // CHECK-LABEL: @while
+// CHECK:       spirv.mlir.loop {
+// CHECK:         spirv.Branch ^[[HEADER:.*]](%{{.*}} : i32)
+// CHECK:       ^[[HEADER]]
+// CHECK:         spirv.BranchConditional %{{.*}}, ^[[BODY:.*]](%{{.*}} : i32), ^[[MERGE:.*]]
+// CHECK:       ^[[BODY]]
+// CHECK:       spirv.Branch
+// CHECK:       ^[[MERGE]]
+// CHECK:         spirv.mlir.merge
+// CHECK:       }
+// CHECK:       spirv.Load "Function"
 func.func @while(%arg0: i32, %arg1: i32) -> i32 {
   %c2_i32 = arith.constant 2 : i32
   %0 = scf.while (%arg3 = %arg0) : (i32) -> (i32) {
@@ -45,3 +55,26 @@ func.func @while(%arg0: i32, %arg1: i32) -> i32 {
   }
   return %0 : i32
 }
+
+// CHECK-LABEL: @for
+// CHECK:       spirv.mlir.loop {
+// CHECK:         spirv.Branch ^[[HEADER:.*]](%{{.*}}, %{{.*}}, %{{.*}} : i32, f32, f32)
+// CHECK:       ^[[HEADER]]
+// CHECK:         spirv.BranchConditional %{{.*}}, ^[[BODY:.*]], ^[[MERGE:.*]]
+// CHECK:       ^[[BODY]]
+// CHECK:         spirv.Branch ^[[HEADER]]
+// CHECK:       ^[[MERGE]]
+// CHECK:         spirv.mlir.merge
+// CHECK:      }
+func.func @for() {
+  %lb = arith.constant 4 : index
+  %ub = arith.constant 42 : index
+  %step = arith.constant 2 : index
+  %s0 = arith.constant 0.0 : f32
+  %s1 = arith.constant 1.0 : f32
+  %result:2 = scf.for %i0 = %lb to %ub step %step iter_args(%si = %s0, %sj = %s1) -> (f32, f32) {
+    %sn = arith.addf %si, %si : f32
+    scf.yield %sn, %sn: f32, f32
+  }
+  return
+}