Preserve analysies in the simplification pass

Fixes a bug at the same time.  In `UpdateDefUse`, if the definition
already exists, we are not suppose to analyse it again.  When you do
the entries for the definition are deleted, and we don't want that.
The check for this was wrong.

1 files changed, 43 insertions, 0 deletions

diff --git a/test/opt/def_use_test.cpp b/test/opt/def_use_test.cpp
index a72f79f8..cdc829be 100644
--- a/test/opt/def_use_test.cpp
+++ b/test/opt/def_use_test.cpp
@@ -22,11 +22,13 @@
 #include "opt/def_use_manager.h"
 #include "opt/ir_context.h"
 #include "opt/module.h"
+#include "pass_fixture.h"
 #include "pass_utils.h"
 #include "spirv-tools/libspirv.hpp"
 
 namespace {
 
+using ::testing::Contains;
 using ::testing::UnorderedElementsAre;
 using ::testing::UnorderedElementsAreArray;
 
@@ -1666,5 +1668,46 @@ INSTANTIATE_TEST_CASE_P(
         },
       },
       }));
+
+using UpdateUsesTest = PassTest<::testing::Test>;
+
+TEST_F(UpdateUsesTest, KeepOldUses) {
+  const std::vector<const char*> text = {
+      // clang-format off
+      "OpCapability Shader",
+      "%1 = OpExtInstImport \"GLSL.std.450\"",
+      "OpMemoryModel Logical GLSL450",
+      "OpEntryPoint Vertex %main \"main\"",
+      "OpName %main \"main\"",
+      "%void = OpTypeVoid",
+      "%4 = OpTypeFunction %void",
+      "%uint = OpTypeInt 32 0",
+      "%uint_5 = OpConstant %uint 5",
+      "%25 = OpConstant %uint 25",
+      "%main = OpFunction %void None %4",
+      "%8 = OpLabel",
+      "%9 = OpIMul %uint %uint_5 %uint_5",
+      "%10 = OpIMul %uint %9 %uint_5",
+      "OpReturn",
+      "OpFunctionEnd"
+      // clang-format on
+  };
+
+  std::unique_ptr<ir::IRContext> context =
+      BuildModule(SPV_ENV_UNIVERSAL_1_1, nullptr, JoinAllInsts(text),
+                  SPV_TEXT_TO_BINARY_OPTION_PRESERVE_NUMERIC_IDS);
+  ASSERT_NE(nullptr, context);
+
+  DefUseManager* def_use_mgr = context->get_def_use_mgr();
+  ir::Instruction* def = def_use_mgr->GetDef(9);
+  ir::Instruction* use = def_use_mgr->GetDef(10);
+  def->SetOpcode(SpvOpCopyObject);
+  def->SetInOperands({{SPV_OPERAND_TYPE_ID, {25}}});
+  context->UpdateDefUse(def);
+
+  auto users = def_use_mgr->id_to_users();
+  opt::analysis::UserEntry entry = {def, use};
+  EXPECT_THAT(users, Contains(entry));
+}
 // clang-format on
 }  // anonymous namespace