From 229ebc06657c1c2186d2ec3dc0add54d82d93c98 Mon Sep 17 00:00:00 2001
From: Alan Baker <alanbaker@google.com>
Date: Wed, 14 Feb 2018 09:39:11 -0500
Subject: [PATCH] Fixes #1295. Mark undef values as varying in ccp.

* Undef now marked as varying in ccp
 * this prevents incorrect meet operations since phis were always not
 interesting
* added a test to catch the bug
---
 source/opt/ccp_pass.cpp | 10 ++++++----
 test/opt/ccp_test.cpp   | 38 ++++++++++++++++++++++++++++++++++++++
 2 files changed, 44 insertions(+), 4 deletions(-)

diff --git a/source/opt/ccp_pass.cpp b/source/opt/ccp_pass.cpp
index 3c85e4f..d81364b 100644
--- a/source/opt/ccp_pass.cpp
+++ b/source/opt/ccp_pass.cpp
@@ -273,10 +273,12 @@ void CCPPass::Initialize(ir::IRContext* c) {
   // Populate the constant table with values from constant declarations in the
   // module.  The values of each OpConstant declaration is the identity
   // assignment (i.e., each constant is its own value).
-  for (const auto& inst : context()->module()->GetConstants()) {
-    // Skip specialization constants.
-    if (inst->IsConstant()) {
-      values_[inst->result_id()] = inst->result_id();
+  for (const auto& inst : get_module()->types_values()) {
+    // Skip specialization constants. Treat undef as varying.
+    if (inst.IsConstant()) {
+      values_[inst.result_id()] = inst.result_id();
+    } else if (inst.opcode() == SpvOpUndef) {
+      values_[inst.result_id()] = kVaryingSSAId;
     }
   }
 }
diff --git a/test/opt/ccp_test.cpp b/test/opt/ccp_test.cpp
index 3ebf65b..a221c42 100644
--- a/test/opt/ccp_test.cpp
+++ b/test/opt/ccp_test.cpp
@@ -641,6 +641,44 @@ OpFunctionEnd
   auto res = SinglePassRunToBinary<opt::CCPPass>(text, true);
   EXPECT_EQ(std::get<1>(res), opt::Pass::Status::SuccessWithoutChange);
 }
+
+TEST_F(CCPTest, UndefInPhi) {
+  const std::string text = R"(
+; CHECK: [[uint1:%\w+]] = OpConstant {{%\w+}} 1
+; CHECK: [[phi:%\w+]] = OpPhi
+; CHECK: OpIAdd {{%\w+}} [[phi]] [[uint1]]
+               OpCapability Kernel
+               OpCapability Linkage
+               OpMemoryModel Logical OpenCL
+               OpDecorate %1 LinkageAttributes "func" Export
+       %void = OpTypeVoid
+       %bool = OpTypeBool
+       %uint = OpTypeInt 32 0
+     %uint_0 = OpConstant %uint 0
+     %uint_1 = OpConstant %uint 1
+          %7 = OpUndef %uint
+          %8 = OpTypeFunction %void %bool
+          %1 = OpFunction %void None %8
+          %9 = OpFunctionParameter %bool
+         %10 = OpLabel
+               OpBranchConditional %9 %11 %12
+         %11 = OpLabel
+               OpBranch %13
+         %12 = OpLabel
+               OpBranch %14
+         %14 = OpLabel
+               OpBranchConditional %9 %13 %15
+         %15 = OpLabel
+               OpBranch %13
+         %13 = OpLabel
+         %16 = OpPhi %uint %uint_0 %11 %7 %14 %uint_1 %15
+         %17 = OpIAdd %uint %16 %uint_1
+               OpReturn
+               OpFunctionEnd
+)";
+
+  SinglePassRunAndMatch<opt::CCPPass>(text, true);
+}
 #endif
 
 }  // namespace
-- 
2.7.4