[spirv] Fix static function variable initialization (#942)

Static function variable should be initialized once. We were
emitting if checks to make sure that but got the branch wrongly
flipped.

tools/clang/lib/SPIRV/SPIRVEmitter.cpp

@@ -3816,15 +3816,17 @@ void SPIRVEmitter::initOnce(QualType varType, std::string varName,
 
   const uint32_t condition = theBuilder.createLoad(boolType, initDoneVar);
 
-  const uint32_t thenBB = theBuilder.createBasicBlock("if.true");
-  const uint32_t mergeBB = theBuilder.createBasicBlock("if.merge");
+  const uint32_t todoBB = theBuilder.createBasicBlock("if.init.todo");
+  const uint32_t doneBB = theBuilder.createBasicBlock("if.init.done");
 
-  theBuilder.createConditionalBranch(condition, thenBB, mergeBB, mergeBB);
-  theBuilder.addSuccessor(thenBB);
-  theBuilder.addSuccessor(mergeBB);
-  theBuilder.setMergeTarget(mergeBB);
+  // If initDoneVar contains true, we jump to the "done" basic block; otherwise,
+  // jump to the "todo" basic block.
+  theBuilder.createConditionalBranch(condition, doneBB, todoBB, doneBB);
+  theBuilder.addSuccessor(todoBB);
+  theBuilder.addSuccessor(doneBB);
+  theBuilder.setMergeTarget(doneBB);
 
-  theBuilder.setInsertPoint(thenBB);
+  theBuilder.setInsertPoint(todoBB);
   // Do initialization and mark done
   if (varInit) {
     theBuilder.createStore(varPtr, doExpr(varInit));
@@ -3833,10 +3835,10 @@ void SPIRVEmitter::initOnce(QualType varType, std::string varName,
     theBuilder.createStore(varPtr, theBuilder.getConstantNull(typeId));
   }
   theBuilder.createStore(initDoneVar, theBuilder.getConstantBool(true));
-  theBuilder.createBranch(mergeBB);
-  theBuilder.addSuccessor(mergeBB);
+  theBuilder.createBranch(doneBB);
+  theBuilder.addSuccessor(doneBB);
 
-  theBuilder.setInsertPoint(mergeBB);
+  theBuilder.setInsertPoint(doneBB);
 }
 
 bool SPIRVEmitter::isVectorShuffle(const Expr *expr) {

tools/clang/test/CodeGenSPIRV/var.static.hlsl

@@ -37,35 +37,35 @@ int main(int input: A) : B {
 // CHECK-LABEL: %bb_entry = OpLabel
 
 // CHECK-NEXT: [[initdonea:%\d+]] = OpLoad %bool %init_done_a
-// CHECK-NEXT: OpSelectionMerge %if_merge None
-// CHECK-NEXT: OpBranchConditional [[initdonea]] %if_true %if_merge
-// CHECK-NEXT: %if_true = OpLabel
+// CHECK-NEXT: OpSelectionMerge %if_init_done None
+// CHECK-NEXT: OpBranchConditional [[initdonea]] %if_init_done %if_init_todo
+// CHECK-NEXT: %if_init_todo = OpLabel
 // CHECK-NEXT: OpStore %a %uint_5
 // CHECK-NEXT: OpStore %init_done_a %true
-// CHECK-NEXT: OpBranch %if_merge
+// CHECK-NEXT: OpBranch %if_init_done
     static uint a = 5;    // const init
-// CHECK-NEXT: %if_merge = OpLabel
+// CHECK-NEXT: %if_init_done = OpLabel
 
 // CHECK-NEXT: [[initdoneb:%\d+]] = OpLoad %bool %init_done_b
-// CHECK-NEXT: OpSelectionMerge %if_merge_0 None
-// CHECK-NEXT: OpBranchConditional [[initdoneb]] %if_true_0 %if_merge_0
-// CHECK-NEXT: %if_true_0 = OpLabel
+// CHECK-NEXT: OpSelectionMerge %if_init_done_0 None
+// CHECK-NEXT: OpBranchConditional [[initdoneb]] %if_init_done_0 %if_init_todo_0
+// CHECK-NEXT: %if_init_todo_0 = OpLabel
 // CHECK-NEXT: OpStore %b [[v4f0]]
 // CHECK-NEXT: OpStore %init_done_b %true
-// CHECK-NEXT: OpBranch %if_merge_0
+// CHECK-NEXT: OpBranch %if_init_done_0
     static float4 b;      // no init
-// CHECK-NEXT: %if_merge_0 = OpLabel
+// CHECK-NEXT: %if_init_done_0 = OpLabel
 
 // CHECK-NEXT: [[initdonec:%\d+]] = OpLoad %bool %init_done_c
-// CHECK-NEXT: OpSelectionMerge %if_merge_1 None
-// CHECK-NEXT: OpBranchConditional [[initdonec]] %if_true_1 %if_merge_1
-// CHECK-NEXT: %if_true_1 = OpLabel
+// CHECK-NEXT: OpSelectionMerge %if_init_done_1 None
+// CHECK-NEXT: OpBranchConditional [[initdonec]] %if_init_done_1 %if_init_todo_1
+// CHECK-NEXT: %if_init_todo_1 = OpLabel
 // CHECK-NEXT: [[initc:%\d+]] = OpLoad %int %input
 // CHECK-NEXT: OpStore %c [[initc]]
 // CHECK-NEXT: OpStore %init_done_c %true
-// CHECK-NEXT: OpBranch %if_merge_1
+// CHECK-NEXT: OpBranch %if_init_done_1
     static int c = input; // var init
-// CHECK-NEXT: %if_merge_1 = OpLabel
+// CHECK-NEXT: %if_init_done_1 = OpLabel
 
     return input;
 }