Fix HInstruction::ReplaceInput(), allow no-op.

Allow HInstruction::ReplaceInput() to be called with
a `replacement` being the same as the old input and
do nothing in that case.

This is a follow-up to
    https://android-review.googlesource.com/216923
where I erroneously assumed that it never happens.

Also adhere to the standard C++ std::forward_list<>
semantics in the single-element overload of
`IntrusiveForwardList<>::splice_after()`.

Bug: 28173563
Change-Id: I5cea14c212b1083f90ffe6b5b53324ad663d57d8

1 files changed, 4 insertions, 1 deletions

diff --git a/compiler/optimizing/nodes.cc b/compiler/optimizing/nodes.cc
index 7c6e9318fb..fe75451ad2 100644
--- a/compiler/optimizing/nodes.cc
+++ b/compiler/optimizing/nodes.cc
@@ -1022,8 +1022,11 @@ void HInstruction::ReplaceWith(HInstruction* other) {
 
 void HInstruction::ReplaceInput(HInstruction* replacement, size_t index) {
   HUserRecord<HInstruction*> input_use = InputRecordAt(index);
+  if (input_use.GetInstruction() == replacement) {
+    // Nothing to do.
+    return;
+  }
   HUseList<HInstruction*>::iterator before_use_node = input_use.GetBeforeUseNode();
-  DCHECK(input_use.GetInstruction() != replacement);
   // Note: fixup_end remains valid across splice_after().
   auto fixup_end =
       replacement->uses_.empty() ? replacement->uses_.begin() : ++replacement->uses_.begin();