From bc09f53c96075e80f4f7e932fabf04f380c73958 Mon Sep 17 00:00:00 2001
From: alan-baker <33432579+alan-baker@users.noreply.github.com>
Date: Wed, 10 Oct 2018 13:25:48 -0400
Subject: [PATCH] Fix calculation of case fall through (#1965)

Fixes #1959

* Code erroneously concluded that the target's fall through was itself
* Added a test
---
 source/val/validate_cfg.cpp |  4 +++-
 test/val/val_cfg_test.cpp   | 34 ++++++++++++++++++++++++++++++++++
 2 files changed, 37 insertions(+), 1 deletion(-)

diff --git a/source/val/validate_cfg.cpp b/source/val/validate_cfg.cpp
index 7e22a27e9..162588aa8 100644
--- a/source/val/validate_cfg.cpp
+++ b/source/val/validate_cfg.cpp
@@ -336,7 +336,9 @@ spv_result_t FindCaseFallThrough(
       }
 
       if (*case_fall_through == 0u) {
-        *case_fall_through = block->id();
+        if (target_block != block) {
+          *case_fall_through = block->id();
+        }
       } else if (*case_fall_through != block->id()) {
         // Case construct has at most one branch to another case construct.
         return _.diag(SPV_ERROR_INVALID_CFG, target_block->label())
diff --git a/test/val/val_cfg_test.cpp b/test/val/val_cfg_test.cpp
index d45fd101b..d1f1a66ae 100644
--- a/test/val/val_cfg_test.cpp
+++ b/test/val/val_cfg_test.cpp
@@ -1777,6 +1777,40 @@ OpFunctionEnd
                 "  OpSwitch %uint_0 %10 0 %11 1 %12 2 %13"));
 }
 
+TEST_F(ValidateCFG, GoodUnreachableSwitch) {
+  const std::string text = R"(
+OpCapability Shader
+OpMemoryModel Logical GLSL450
+OpEntryPoint Fragment %2 "main"
+OpExecutionMode %2 OriginUpperLeft
+%3 = OpTypeVoid
+%4 = OpTypeFunction %3
+%5 = OpTypeBool
+%6 = OpConstantTrue %5
+%7 = OpTypeInt 32 1
+%9 = OpConstant %7 0
+%2 = OpFunction %3 None %4
+%10 = OpLabel
+OpSelectionMerge %11 None
+OpBranchConditional %6 %12 %13
+%12 = OpLabel
+OpReturn
+%13 = OpLabel
+OpReturn
+%11 = OpLabel
+OpSelectionMerge %14 None
+OpSwitch %9 %14 0 %15
+%15 = OpLabel
+OpBranch %14
+%14 = OpLabel
+OpReturn
+OpFunctionEnd
+)";
+
+  CompileSuccessfully(text);
+  EXPECT_THAT(SPV_SUCCESS, ValidateInstructions());
+}
+
 TEST_F(ValidateCFG, InvalidCaseExit) {
   const std::string text = R"(
 OpCapability Shader