[ir][spirv-writer] Emit load instructions

Bug: tint:1906
Change-Id: I86396d0eaa7886f010cf037c2b1253014146d37c
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/133225
Kokoro: Kokoro <noreply+kokoro@google.com>
Commit-Queue: James Price <jrprice@google.com>
Reviewed-by: Dan Sinclair <dsinclair@chromium.org>

src/tint/writer/spirv/ir/generator_impl_ir.cc

@@ -19,6 +19,7 @@
 #include "src/tint/ir/block.h"
 #include "src/tint/ir/function_terminator.h"
 #include "src/tint/ir/if.h"
+#include "src/tint/ir/load.h"
 #include "src/tint/ir/module.h"
 #include "src/tint/ir/store.h"
 #include "src/tint/ir/transform/add_empty_entry_point.h"
@@ -296,6 +297,7 @@ void GeneratorImplIr::EmitBlock(const ir::Block* block) {
         auto result = Switch(
             inst,  //
             [&](const ir::Binary* b) { return EmitBinary(b); },
+            [&](const ir::Load* l) { return EmitLoad(l); },
             [&](const ir::Store* s) {
                 EmitStore(s);
                 return 0u;
@@ -396,6 +398,12 @@ uint32_t GeneratorImplIr::EmitBinary(const ir::Binary* binary) {
     return id;
 }
 
+uint32_t GeneratorImplIr::EmitLoad(const ir::Load* load) {
+    auto id = module_.NextId();
+    current_function_.push_inst(spv::Op::OpLoad, {Type(load->Type()), id, Value(load->from)});
+    return id;
+}
+
 void GeneratorImplIr::EmitStore(const ir::Store* store) {
     current_function_.push_inst(spv::Op::OpStore, {Value(store->to), Value(store->from)});
 }

src/tint/writer/spirv/ir/generator_impl_ir.h

@@ -32,6 +32,7 @@ class Binary;
 class Block;
 class If;
 class Function;
+class Load;
 class Module;
 class Store;
 class Value;
@@ -106,6 +107,11 @@ class GeneratorImplIr {
     /// @returns the result ID of the instruction
     uint32_t EmitBinary(const ir::Binary* binary);
 
+    /// Emit a load instruction.
+    /// @param load the load instruction to emit
+    /// @returns the result ID of the instruction
+    uint32_t EmitLoad(const ir::Load* load);
+
     /// Emit a store instruction.
     /// @param store the store instruction to emit
     void EmitStore(const ir::Store* store);

src/tint/writer/spirv/ir/generator_impl_ir_var_test.cc

@@ -138,6 +138,32 @@ OpFunctionEnd
 )");
 }
 
+TEST_F(SpvGeneratorImplTest, FunctionVar_Load) {
+    auto* func = b.CreateFunction(mod.symbols.Register("foo"), mod.types.Get<type::Void>());
+    b.Branch(func->start_target, func->end_target);
+
+    auto* store_ty = mod.types.Get<type::I32>();
+    auto* ty = mod.types.Get<type::Pointer>(store_ty, builtin::AddressSpace::kFunction,
+                                            builtin::Access::kReadWrite);
+    auto* v = b.Declare(ty);
+    func->start_target->instructions.Push(v);
+    func->start_target->instructions.Push(b.Load(v));
+
+    generator_.EmitFunction(func);
+    EXPECT_EQ(DumpModule(generator_.Module()), R"(OpName %1 "foo"
+%2 = OpTypeVoid
+%3 = OpTypeFunction %2
+%7 = OpTypeInt 32 1
+%6 = OpTypePointer Function %7
+%1 = OpFunction %2 None %3
+%4 = OpLabel
+%5 = OpVariable %6 Function
+%8 = OpLoad %7 %5
+OpReturn
+OpFunctionEnd
+)");
+}
+
 TEST_F(SpvGeneratorImplTest, FunctionVar_Store) {
     auto* func = b.CreateFunction(mod.symbols.Register("foo"), mod.types.Get<type::Void>());
     b.Branch(func->start_target, func->end_target);