[spirv-reader] Refine selection construct concept

Distinguish between selections constructs starting with with
OpBranchConditional and those starting with OpSwitch.

We'll use this in a followup CL to track break from a switch.

Bug: tint:3
Change-Id: I8d000cb42325535a4937c84f83a83c98a9b8d4c5
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/21080
Reviewed-by: dan sinclair <dsinclair@google.com>

src/reader/spirv/construct.h

@@ -31,10 +31,16 @@ namespace spirv {
 struct Construct {
   /// Enumeration for the kinds of structured constructs.
   enum Kind {
-    kFunction,   // The whole function.
+    /// The whole function.
-    kSelection,  // A SPIR-V selection construct
+    kFunction,
-    kLoop,       // A SPIR-V loop construct
+    /// A SPIR-V selection construct, header ending in OpBrancConditional
-    kContinue,   // A SPIR-V continue construct
+    kIfSelection,
+    /// A SPIR-V selection construct, header ending in OpSwitch
+    kSwitchSelection,
+    /// A SPIR-V loop construct
+    kLoop,
+    /// A SPIR-V continue construct
+    kContinue,
   };
 
   /// Constructor
@@ -94,8 +100,10 @@ inline std::string ToString(Construct::Kind kind) {
   switch (kind) {
     case Construct::kFunction:
       return "Function";
-    case Construct::kSelection:
+    case Construct::kIfSelection:
-      return "Selection";
+      return "IfSelection";
+    case Construct::kSwitchSelection:
+      return "SwitchSelection";
     case Construct::kLoop:
       return "Loop";
     case Construct::kContinue:

src/reader/spirv/function.cc

@@ -791,7 +791,12 @@ bool FunctionEmitter::LabelControlFlowConstructs() {
         // From the interval rule, the selection construct consists of blocks
         // in the block order, starting at the header, until just before the
         // merge block.
-        top = push_construct(depth, Construct::kSelection, header, merge);
+        const auto branch_opcode =
+            header_info->basic_block->terminator()->opcode();
+        const auto kind = (branch_opcode == SpvOpBranchConditional)
+                              ? Construct::kIfSelection
+                              : Construct::kSwitchSelection;
+        top = push_construct(depth, kind, header, merge);
       }
     }
 
@@ -819,14 +824,11 @@ bool FunctionEmitter::FindSwitchCaseHeaders() {
     return false;
   }
   for (auto& construct : constructs_) {
-    if (construct->kind != Construct::kSelection) {
+    if (construct->kind != Construct::kSwitchSelection) {
       continue;
     }
     const auto* branch =
         GetBlockInfo(construct->begin_id)->basic_block->terminator();
-    if (branch->opcode() != SpvOpSwitch) {
-      continue;
-    }
 
     // Mark the default block
     const auto default_id = branch->GetSingleWordInOperand(1);

src/reader/spirv/function.h

@@ -43,17 +43,24 @@ enum class EdgeKind {
   // A back-edge: An edge from a node to one of its ancestors in a depth-first
   // search from the entry block.
   kBack,
-  // An edge from a node to the merge block of the nearest enclosing structured
+  // An edge from a node to the merge block of the nearest enclosing switch,
-  // construct.  We write "ToMerge" to make it clear the destination block is
+  // where there is no intervening loop.
-  // the merge block, not the source block.
+  kSwitchBreak,
-  kToMerge,
+  // An edge from a node to the merge block of the nearest enclosing loop, where
-  // An edge from a node to the merge block of the nearest enclosing loop.
+  // there is no intervening switch.
   // The source block is a "break block" as defined by SPIR-V.
   kLoopBreak,
   // An edge from a node in a loop body to the associated continue target, where
   // there are no other intervening loops or switches.
   // The source block is a "continue block" as defined by SPIR-V.
   kLoopContinue,
+  // An edge from a node to the merge block of the nearest enclosing structured
+  // construct, but which is neither a kSwitchBreak or a kLoopBreak.
+  // This can only occur for an "if" selection, i.e. where the selection
+  // header ends in OpBranchConditional.
+  // TODO(dneto): Rename this to kIfBreak after we correctly classify edges
+  // as kSwitchBreak.
+  kToMerge,
   // An edge from one switch case to the next sibling switch case.
   kCaseFallThrough,
   // None of the above. By structured control flow rules, there can be at most

src/reader/spirv/function_cfg_test.cc

@@ -2847,7 +2847,7 @@ TEST_F(SpvParserTest,
   EXPECT_EQ(constructs.size(), 2u);
   EXPECT_THAT(ToString(constructs), Eq(R"(ConstructList{
   Construct{ Function [0,4) begin_id:10 end_id:0 depth:0 parent:null }
-  Construct{ Selection [0,3) begin_id:10 end_id:99 depth:1 parent:Function@10 }
+  Construct{ IfSelection [0,3) begin_id:10 end_id:99 depth:1 parent:Function@10 }
 })")) << constructs;
   // The block records the nearest enclosing construct.
   EXPECT_EQ(fe.GetBlockInfo(10)->construct, constructs[1].get());
@@ -2894,7 +2894,7 @@ TEST_F(
   EXPECT_EQ(constructs.size(), 2u);
   EXPECT_THAT(ToString(constructs), Eq(R"(ConstructList{
   Construct{ Function [0,6) begin_id:5 end_id:0 depth:0 parent:null }
-  Construct{ Selection [1,4) begin_id:10 end_id:99 depth:1 parent:Function@5 }
+  Construct{ IfSelection [1,4) begin_id:10 end_id:99 depth:1 parent:Function@5 }
 })")) << constructs;
   // The block records the nearest enclosing construct.
   EXPECT_EQ(fe.GetBlockInfo(5)->construct, constructs[0].get());
@@ -2938,7 +2938,7 @@ TEST_F(SpvParserTest, LabelControlFlowConstructs_SwitchSelection) {
   EXPECT_EQ(constructs.size(), 2u);
   EXPECT_THAT(ToString(constructs), Eq(R"(ConstructList{
   Construct{ Function [0,5) begin_id:10 end_id:0 depth:0 parent:null }
-  Construct{ Selection [0,4) begin_id:10 end_id:99 depth:1 parent:Function@10 }
+  Construct{ SwitchSelection [0,4) begin_id:10 end_id:99 depth:1 parent:Function@10 }
 })")) << constructs;
   // The block records the nearest enclosing construct.
   EXPECT_EQ(fe.GetBlockInfo(10)->construct, constructs[1].get());
@@ -3070,7 +3070,7 @@ TEST_F(SpvParserTest,
   // it.
   EXPECT_THAT(ToString(constructs), Eq(R"(ConstructList{
   Construct{ Function [0,4) begin_id:10 end_id:0 depth:0 parent:null }
-  Construct{ Selection [0,2) begin_id:10 end_id:50 depth:1 parent:Function@10 }
+  Construct{ IfSelection [0,2) begin_id:10 end_id:50 depth:1 parent:Function@10 }
   Construct{ Continue [2,3) begin_id:50 end_id:99 depth:1 parent:Function@10 in-c:Continue@50 }
 })")) << constructs;
   // The block records the nearest enclosing construct.
@@ -3117,7 +3117,7 @@ TEST_F(SpvParserTest,
   EXPECT_EQ(constructs.size(), 4u);
   EXPECT_THAT(ToString(constructs), Eq(R"(ConstructList{
   Construct{ Function [0,5) begin_id:10 end_id:0 depth:0 parent:null }
-  Construct{ Selection [0,2) begin_id:10 end_id:50 depth:1 parent:Function@10 }
+  Construct{ IfSelection [0,2) begin_id:10 end_id:50 depth:1 parent:Function@10 }
   Construct{ Continue [3,4) begin_id:60 end_id:99 depth:1 parent:Function@10 in-c:Continue@60 }
   Construct{ Loop [2,3) begin_id:50 end_id:60 depth:1 parent:Function@10 in-c-l:Loop@50 }
 })")) << constructs;
@@ -3176,9 +3176,9 @@ TEST_F(SpvParserTest, LabelControlFlowConstructs_Nest_If_If) {
   EXPECT_EQ(constructs.size(), 4u);
   EXPECT_THAT(ToString(constructs), Eq(R"(ConstructList{
   Construct{ Function [0,9) begin_id:10 end_id:0 depth:0 parent:null }
-  Construct{ Selection [0,8) begin_id:10 end_id:99 depth:1 parent:Function@10 }
+  Construct{ IfSelection [0,8) begin_id:10 end_id:99 depth:1 parent:Function@10 }
-  Construct{ Selection [1,3) begin_id:20 end_id:40 depth:2 parent:Selection@10 }
+  Construct{ IfSelection [1,3) begin_id:20 end_id:40 depth:2 parent:IfSelection@10 }
-  Construct{ Selection [5,7) begin_id:50 end_id:89 depth:2 parent:Selection@10 }
+  Construct{ IfSelection [5,7) begin_id:50 end_id:89 depth:2 parent:IfSelection@10 }
 })")) << constructs;
   // The block records the nearest enclosing construct.
   EXPECT_EQ(fe.GetBlockInfo(10)->construct, constructs[1].get());
@@ -3237,9 +3237,9 @@ TEST_F(SpvParserTest, LabelControlFlowConstructs_Nest_Switch_If) {
   // The ordering among siblings depends on the computed block order.
   EXPECT_THAT(ToString(constructs), Eq(R"(ConstructList{
   Construct{ Function [0,8) begin_id:10 end_id:0 depth:0 parent:null }
-  Construct{ Selection [0,7) begin_id:10 end_id:99 depth:1 parent:Function@10 }
+  Construct{ SwitchSelection [0,7) begin_id:10 end_id:99 depth:1 parent:Function@10 }
-  Construct{ Selection [1,3) begin_id:50 end_id:89 depth:2 parent:Selection@10 }
+  Construct{ IfSelection [1,3) begin_id:50 end_id:89 depth:2 parent:SwitchSelection@10 }
-  Construct{ Selection [4,6) begin_id:20 end_id:49 depth:2 parent:Selection@10 }
+  Construct{ IfSelection [4,6) begin_id:20 end_id:49 depth:2 parent:SwitchSelection@10 }
 })")) << constructs;
   // The block records the nearest enclosing construct.
   EXPECT_EQ(fe.GetBlockInfo(10)->construct, constructs[1].get());
@@ -3286,8 +3286,8 @@ TEST_F(SpvParserTest, LabelControlFlowConstructs_Nest_If_Switch) {
   EXPECT_EQ(constructs.size(), 3u);
   EXPECT_THAT(ToString(constructs), Eq(R"(ConstructList{
   Construct{ Function [0,5) begin_id:10 end_id:0 depth:0 parent:null }
-  Construct{ Selection [0,4) begin_id:10 end_id:99 depth:1 parent:Function@10 }
+  Construct{ IfSelection [0,4) begin_id:10 end_id:99 depth:1 parent:Function@10 }
-  Construct{ Selection [1,3) begin_id:20 end_id:89 depth:2 parent:Selection@10 }
+  Construct{ SwitchSelection [1,3) begin_id:20 end_id:89 depth:2 parent:IfSelection@10 }
 })")) << constructs;
   // The block records the nearest enclosing construct.
   EXPECT_EQ(fe.GetBlockInfo(10)->construct, constructs[1].get());
@@ -3397,7 +3397,7 @@ TEST_F(SpvParserTest, LabelControlFlowConstructs_Nest_Loop_If) {
   Construct{ Function [0,7) begin_id:10 end_id:0 depth:0 parent:null }
   Construct{ Continue [5,6) begin_id:80 end_id:99 depth:1 parent:Function@10 in-c:Continue@80 }
   Construct{ Loop [1,5) begin_id:20 end_id:80 depth:1 parent:Function@10 in-c-l:Loop@20 }
-  Construct{ Selection [2,4) begin_id:30 end_id:49 depth:2 parent:Loop@20 in-c-l:Loop@20 }
+  Construct{ IfSelection [2,4) begin_id:30 end_id:49 depth:2 parent:Loop@20 in-c-l:Loop@20 }
 })")) << constructs;
   // The block records the nearest enclosing construct.
   EXPECT_EQ(fe.GetBlockInfo(10)->construct, constructs[0].get());
@@ -3448,7 +3448,7 @@ TEST_F(SpvParserTest, LabelControlFlowConstructs_Nest_LoopContinue_If) {
   Construct{ Function [0,6) begin_id:10 end_id:0 depth:0 parent:null }
   Construct{ Continue [2,5) begin_id:30 end_id:99 depth:1 parent:Function@10 in-c:Continue@30 }
   Construct{ Loop [1,2) begin_id:20 end_id:30 depth:1 parent:Function@10 in-c-l:Loop@20 }
-  Construct{ Selection [2,4) begin_id:30 end_id:49 depth:2 parent:Continue@30 in-c:Continue@30 }
+  Construct{ IfSelection [2,4) begin_id:30 end_id:49 depth:2 parent:Continue@30 in-c:Continue@30 }
 })")) << constructs;
   // The block records the nearest enclosing construct.
   EXPECT_EQ(fe.GetBlockInfo(10)->construct, constructs[0].get());
@@ -3490,8 +3490,8 @@ TEST_F(SpvParserTest, LabelControlFlowConstructs_Nest_If_SingleBlockLoop) {
   EXPECT_EQ(constructs.size(), 3u);
   EXPECT_THAT(ToString(constructs), Eq(R"(ConstructList{
   Construct{ Function [0,4) begin_id:10 end_id:0 depth:0 parent:null }
-  Construct{ Selection [0,3) begin_id:10 end_id:99 depth:1 parent:Function@10 }
+  Construct{ IfSelection [0,3) begin_id:10 end_id:99 depth:1 parent:Function@10 }
-  Construct{ Continue [1,2) begin_id:20 end_id:89 depth:2 parent:Selection@10 in-c:Continue@20 }
+  Construct{ Continue [1,2) begin_id:20 end_id:89 depth:2 parent:IfSelection@10 in-c:Continue@20 }
 })")) << constructs;
   // The block records the nearest enclosing construct.
   EXPECT_EQ(fe.GetBlockInfo(10)->construct, constructs[1].get());
@@ -3539,9 +3539,9 @@ TEST_F(SpvParserTest, LabelControlFlowConstructs_Nest_If_MultiBlockLoop) {
   EXPECT_EQ(constructs.size(), 4u);
   EXPECT_THAT(ToString(constructs), Eq(R"(ConstructList{
   Construct{ Function [0,7) begin_id:10 end_id:0 depth:0 parent:null }
-  Construct{ Selection [0,6) begin_id:10 end_id:99 depth:1 parent:Function@10 }
+  Construct{ IfSelection [0,6) begin_id:10 end_id:99 depth:1 parent:Function@10 }
-  Construct{ Continue [3,5) begin_id:40 end_id:89 depth:2 parent:Selection@10 in-c:Continue@40 }
+  Construct{ Continue [3,5) begin_id:40 end_id:89 depth:2 parent:IfSelection@10 in-c:Continue@40 }
-  Construct{ Loop [1,3) begin_id:20 end_id:40 depth:2 parent:Selection@10 in-c-l:Loop@20 }
+  Construct{ Loop [1,3) begin_id:20 end_id:40 depth:2 parent:IfSelection@10 in-c-l:Loop@20 }
 })")) << constructs;
   // The block records the nearest enclosing construct.
   EXPECT_EQ(fe.GetBlockInfo(10)->construct, constructs[1].get());