From 89013c6f76568736cd6d8395f73db53045303412 Mon Sep 17 00:00:00 2001
From: Yuanzhong Xu <yuanzx@google.com>
Date: Mon, 25 Jun 2018 17:27:30 -0700
Subject: [XLA] Avoid fusion nodes to have duplicate operands during replacing
 uses.

PiperOrigin-RevId: 202049336
---
 tensorflow/compiler/xla/service/hlo_computation.cc | 69 +++++++++++++++++-----
 1 file changed, 54 insertions(+), 15 deletions(-)

(limited to 'tensorflow/compiler/xla/service/hlo_computation.cc')

diff --git a/tensorflow/compiler/xla/service/hlo_computation.cc b/tensorflow/compiler/xla/service/hlo_computation.cc
index c057be8201..34b18b0e21 100644
--- a/tensorflow/compiler/xla/service/hlo_computation.cc
+++ b/tensorflow/compiler/xla/service/hlo_computation.cc
@@ -120,6 +120,30 @@ HloInstruction* HloComputation::AddParameter(
   return instructions_.back().get();
 }
 
+namespace {
+
+// Returns the new name for a fusion parameter when we change its number.
+//
+// Fusion parameters are named foo.param_1, bar.param_2, etc. We are
+// renumbering the parameters, so replace the final number in the name with
+// the updated value.
+string RenameFusionParameter(const string& original_name, int64 new_param_no) {
+  const string param_underscore = ".param_";
+  size_t index = original_name.rfind(param_underscore);
+  if (index == string::npos) {
+    return original_name;
+  }
+  string after_param = original_name.substr(index + param_underscore.size());
+  int64 numeric_suffix;
+  if (tensorflow::strings::safe_strto64(after_param, &numeric_suffix)) {
+    return StrCat(original_name.substr(0, index + param_underscore.size()),
+                  new_param_no);
+  }
+  return original_name;
+}
+
+}  // namespace
+
 Status HloComputation::RemoveParameter(int64 param_no) {
   CHECK_GE(param_no, 0);
   CHECK_LT(param_no, param_instructions_.size());
@@ -132,21 +156,8 @@ Status HloComputation::RemoveParameter(int64 param_no) {
 
   while (param_no < param_instructions_.size()) {
     param_instruction = param_instructions_[param_no];
-    string param_name = param_instruction->name();
-    // Fusion parameters are named foo.param_1, bar.param_2, etc. We are
-    // renumbering the parameters, so replace the final number in the name with
-    // the updated value.
-    const string param_underscore = ".param_";
-    size_t index = param_name.rfind(param_underscore);
-    if (index == string::npos) {
-      string after_param = name().substr(index + param_underscore.size());
-      int64 numeric_suffix;
-      if (tensorflow::strings::safe_strto64(after_param, &numeric_suffix)) {
-        param_name =
-            StrCat(param_name.substr(0, index), param_underscore, param_no);
-      }
-    }
-
+    string param_name =
+        RenameFusionParameter(param_instruction->name(), param_no);
     HloInstruction* new_instr =
         AddInstructionInternal(HloInstruction::CreateParameter(
             param_no, param_instruction->shape(), param_name));
@@ -159,6 +170,34 @@ Status HloComputation::RemoveParameter(int64 param_no) {
   return Status::OK();
 }
 
+Status HloComputation::RemoveUnusedParameters() {
+  CHECK(IsFusionComputation());
+  int64 removed = 0;
+  for (int64 i = 0; i < param_instructions_.size(); ++i) {
+    HloInstruction* param_instruction = param_instructions_[i];
+    if (param_instruction->user_count() == 0 &&
+        param_instruction != root_instruction()) {
+      TF_RETURN_IF_ERROR(RemoveInstruction(param_instruction));
+      ++removed;
+      continue;
+    }
+
+    if (removed > 0) {
+      const int64 param_no = i - removed;
+      string param_name =
+          RenameFusionParameter(param_instruction->name(), param_no);
+      HloInstruction* new_instr =
+          AddInstructionInternal(HloInstruction::CreateParameter(
+              param_no, param_instruction->shape(), param_name));
+      TF_RETURN_IF_ERROR(param_instruction->ReplaceAllUsesWith(new_instr));
+      param_instructions_[param_no] = new_instr;
+      TF_RETURN_IF_ERROR(RemoveInstruction(param_instruction));
+    }
+  }
+  param_instructions_.resize(param_instructions_.size() - removed);
+  return Status::OK();
+}
+
 bool HloComputation::IsRemovable(const HloInstruction* instruction) {
   // If the instruction has control predecessors or successors then we cannot
   // remove the instruction without violating ordering constraints (added, for
-- 
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