[ir] Convert tests to use disassembler.

This Cl updates the flow node tests to compare against a disassembled
output instead of explicit expect statements. This makes it easier to
see the structure of the IR and to determine any changes.

Bug: tint:1718
Change-Id: I5b8ab42ada4ba902e8937099c7058a39533f2010
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/116548
Reviewed-by: Ben Clayton <bclayton@google.com>
Kokoro: Kokoro <noreply+kokoro@google.com>
Commit-Queue: Dan Sinclair <dsinclair@chromium.org>

src/tint/ir/block.h

@@ -31,6 +31,10 @@ class Block : public Castable<Block, FlowNode> {
     Block();
     ~Block() override;
 
+    /// @returns true if this is a dead block. This can happen in the case like a loop merge block
+    /// which is never reached.
+    bool IsDead() const { return branch.target == nullptr; }
+
     /// The node this block branches too.
     Branch branch = {};
 

src/tint/ir/disassembler.cc

@@ -68,6 +68,8 @@ void Disassembler::EmitBlockInstructions(const Block* b) {
 }
 
 size_t Disassembler::GetIdForNode(const FlowNode* node) {
+    TINT_ASSERT(IR, node);
+
     auto it = flow_node_to_id_.find(node);
     if (it != flow_node_to_id_.end()) {
         return it->second;
@@ -97,6 +99,12 @@ void Disassembler::Walk(const FlowNode* node) {
             Walk(f->end_target);
         },
         [&](const ir::Block* b) {
+            // If this block is dead, nothing to do
+            if (b->IsDead()) {
+                Indent() << "# Dead" << std::endl;
+                return;
+            }
+
             Indent() << "%bb" << GetIdForNode(b) << " = Block" << std::endl;
             EmitBlockInstructions(b);
 
@@ -113,7 +121,11 @@ void Disassembler::Walk(const FlowNode* node) {
                 }
                 v->ToString(out_, mod_.symbols);
             }
-            out_ << ")" << std::endl << std::endl;
+            out_ << ")" << std::endl;
+
+            if (!b->branch.target->Is<Terminator>()) {
+                out_ << std::endl;
+            }
 
             Walk(b->branch.target);
         },
@@ -128,14 +140,17 @@ void Disassembler::Walk(const FlowNode* node) {
                 for (const auto& c : s->cases) {
                     Indent() << "# Case ";
                     for (const auto& selector : c.selectors) {
+                        if (&selector != &c.selectors.Front()) {
+                            out_ << " ";
+                        }
+
                         if (selector.IsDefault()) {
-                            out_ << "default ";
+                            out_ << "default";
                         } else {
                             selector.val->ToString(out_, mod_.symbols);
                         }
                     }
                     out_ << std::endl;
-                    ScopedIndent case_indent(&indent_size_);
                     Walk(c.start.target);
                 }
             }
@@ -159,8 +174,10 @@ void Disassembler::Walk(const FlowNode* node) {
                 Walk(i->false_.target);
             }
 
-            Indent() << "# if merge" << std::endl;
-            Walk(i->merge.target);
+            if (!i->merge.target->IsDisconnected()) {
+                Indent() << "# if merge" << std::endl;
+                Walk(i->merge.target);
+            }
         },
         [&](const ir::Loop* l) {
             Indent() << "%bb" << GetIdForNode(l) << " = loop" << std::endl;
@@ -174,7 +191,6 @@ void Disassembler::Walk(const FlowNode* node) {
                 }
 
                 Indent() << "# loop continuing" << std::endl;
-                ScopedIndent continuing_indent(&indent_size_);
                 Walk(l->continuing.target);
             }
 

src/tint/ir/flow_node.h

@@ -32,6 +32,9 @@ class FlowNode : public Castable<FlowNode> {
     ///   - Node is a continue target outside control flow (loop that returns)
     utils::Vector<FlowNode*, 2> inbound_branches;
 
+    /// @returns true if this node has no inbound branches
+    bool IsDisconnected() const { return inbound_branches.IsEmpty(); }
+
   protected:
     /// Constructor
     FlowNode();

src/tint/ir/if.h

@@ -37,7 +37,7 @@ class If : public Castable<If, FlowNode> {
     Branch true_ = {};
     /// The false branch block
     Branch false_ = {};
-    /// An block to reconvert the true/false barnches. The block always exists, but there maybe no
+    /// An block to converge the true/false branches. The block always exists, but there maybe no
     /// branches into it. (e.g. if both branches `return`)
     Branch merge = {};
     /// Value holding the condition result

src/tint/ir/test_helper.h

@@ -92,6 +92,13 @@ class TestHelperBase : public BASE, public ProgramBuilder {
         return gen_->FlowNodeForAstNode(node);
     }
 
+    /// @param mod the module
+    /// @returns the disassembly string of the module
+    std::string Disassemble(Module& mod) const {
+        Disassembler d(mod);
+        return d.Disassemble();
+    }
+
     /// @returns the error generated during build, if any
     std::string Error() const { return error_; }