Add while statement parsing.

This CL adds parsing for the WGSL `while` statement.

Bug: tint:1425
Change-Id: Ibce5e28568935ca4f51b5ac33e7a60af7a916b4a
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/93540
Reviewed-by: Ben Clayton <bclayton@google.com>
Kokoro: Kokoro <noreply+kokoro@google.com>
Commit-Queue: Dan Sinclair <dsinclair@chromium.org>

test/tint/BUILD.gn

@@ -211,6 +211,7 @@ tint_unittests_source_set("tint_unittests_ast_src") {
     "../../src/tint/ast/variable_decl_statement_test.cc",
     "../../src/tint/ast/variable_test.cc",
     "../../src/tint/ast/vector_test.cc",
+    "../../src/tint/ast/while_statement_test.cc",
     "../../src/tint/ast/workgroup_attribute_test.cc",
   ]
 }
@@ -307,8 +308,8 @@ tint_unittests_source_set("tint_unittests_sem_src") {
     "../../src/tint/sem/sem_struct_test.cc",
     "../../src/tint/sem/storage_texture_test.cc",
     "../../src/tint/sem/texture_test.cc",
-    "../../src/tint/sem/type_test.cc",
     "../../src/tint/sem/type_manager_test.cc",
+    "../../src/tint/sem/type_test.cc",
     "../../src/tint/sem/u32_test.cc",
     "../../src/tint/sem/vector_test.cc",
   ]
@@ -359,6 +360,7 @@ tint_unittests_source_set("tint_unittests_transform_src") {
     "../../src/tint/transform/var_for_dynamic_index_test.cc",
     "../../src/tint/transform/vectorize_scalar_matrix_constructors_test.cc",
     "../../src/tint/transform/vertex_pulling_test.cc",
+    "../../src/tint/transform/while_to_loop_test.cc",
     "../../src/tint/transform/wrap_arrays_in_structs_test.cc",
     "../../src/tint/transform/zero_init_workgroup_memory_test.cc",
   ]
@@ -552,6 +554,7 @@ tint_unittests_source_set("tint_unittests_wgsl_reader_src") {
     "../../src/tint/reader/wgsl/parser_impl_variable_ident_decl_test.cc",
     "../../src/tint/reader/wgsl/parser_impl_variable_qualifier_test.cc",
     "../../src/tint/reader/wgsl/parser_impl_variable_stmt_test.cc",
+    "../../src/tint/reader/wgsl/parser_impl_while_stmt_test.cc",
     "../../src/tint/reader/wgsl/parser_test.cc",
     "../../src/tint/reader/wgsl/token_test.cc",
   ]

test/tint/loops/while.wgsl

@@ -0,0 +1,7 @@
+fn f() -> i32 {
+    var i : i32;
+    while (i < 4) {
+        i = i + 1;
+    }
+    return i;
+}

test/tint/loops/while.wgsl.expected.glsl

@@ -0,0 +1,14 @@
+#version 310 es
+
+layout(local_size_x = 1, local_size_y = 1, local_size_z = 1) in;
+void unused_entry_point() {
+  return;
+}
+int f() {
+  int i = 0;
+  while((i < 4)) {
+    i = (i + 1);
+  }
+  return i;
+}
+

test/tint/loops/while.wgsl.expected.hlsl

@@ -0,0 +1,12 @@
+[numthreads(1, 1, 1)]
+void unused_entry_point() {
+  return;
+}
+
+int f() {
+  int i = 0;
+  [loop] while((i < 4)) {
+    i = (i + 1);
+  }
+  return i;
+}

test/tint/loops/while.wgsl.expected.msl

@@ -0,0 +1,11 @@
+#include <metal_stdlib>
+
+using namespace metal;
+int f() {
+  int i = 0;
+  while((i < 4)) {
+    i = as_type<int>((as_type<uint>(i) + as_type<uint>(1)));
+  }
+  return i;
+}
+

test/tint/loops/while.wgsl.expected.spvasm

@@ -0,0 +1,51 @@
+; SPIR-V
+; Version: 1.3
+; Generator: Google Tint Compiler; 0
+; Bound: 27
+; Schema: 0
+               OpCapability Shader
+               OpMemoryModel Logical GLSL450
+               OpEntryPoint GLCompute %unused_entry_point "unused_entry_point"
+               OpExecutionMode %unused_entry_point LocalSize 1 1 1
+               OpName %unused_entry_point "unused_entry_point"
+               OpName %f "f"
+               OpName %i "i"
+       %void = OpTypeVoid
+          %1 = OpTypeFunction %void
+        %int = OpTypeInt 32 1
+          %5 = OpTypeFunction %int
+%_ptr_Function_int = OpTypePointer Function %int
+         %11 = OpConstantNull %int
+      %int_4 = OpConstant %int 4
+       %bool = OpTypeBool
+      %int_1 = OpConstant %int 1
+%unused_entry_point = OpFunction %void None %1
+          %4 = OpLabel
+               OpReturn
+               OpFunctionEnd
+          %f = OpFunction %int None %5
+          %8 = OpLabel
+          %i = OpVariable %_ptr_Function_int Function %11
+               OpBranch %12
+         %12 = OpLabel
+               OpLoopMerge %13 %14 None
+               OpBranch %15
+         %15 = OpLabel
+         %17 = OpLoad %int %i
+         %19 = OpSLessThan %bool %17 %int_4
+         %16 = OpLogicalNot %bool %19
+               OpSelectionMerge %21 None
+               OpBranchConditional %16 %22 %21
+         %22 = OpLabel
+               OpBranch %13
+         %21 = OpLabel
+         %23 = OpLoad %int %i
+         %25 = OpIAdd %int %23 %int_1
+               OpStore %i %25
+               OpBranch %14
+         %14 = OpLabel
+               OpBranch %12
+         %13 = OpLabel
+         %26 = OpLoad %int %i
+               OpReturnValue %26
+               OpFunctionEnd

test/tint/loops/while.wgsl.expected.wgsl

@@ -0,0 +1,7 @@
+fn f() -> i32 {
+  var i : i32;
+  while((i < 4)) {
+    i = (i + 1);
+  }
+  return i;
+}