[NFC] Instruction: introduce replaceSuccessorWith() function, use it

Summary:
There is `Instruction::getNumSuccessors()`, `Instruction::getSuccessor()`
and `Instruction::setSuccessor()`, but no function to replace every
specified `BasicBlock*` successor with some other specified `BasicBlock*`.
I've found one place where it should clearly be used.

Reviewers: chandlerc, craig.topper, spatel, danielcdh

Reviewed By: craig.topper

Subscribers: llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D61010

llvm-svn: 359994

1 files changed, 7 insertions, 0 deletions

diff --git a/llvm/lib/IR/Instruction.cpp b/llvm/lib/IR/Instruction.cpp
index f15bd601727..42a7a1cce7f 100644
--- a/llvm/lib/IR/Instruction.cpp
+++ b/llvm/lib/IR/Instruction.cpp
@@ -675,6 +675,13 @@ void Instruction::setSuccessor(unsigned idx, BasicBlock *B) {
   llvm_unreachable("not a terminator");
 }
 
+void Instruction::replaceSuccessorWith(BasicBlock *OldBB, BasicBlock *NewBB) {
+  for (unsigned Idx = 0, NumSuccessors = Instruction::getNumSuccessors();
+       Idx != NumSuccessors; ++Idx)
+    if (getSuccessor(Idx) == OldBB)
+      setSuccessor(Idx, NewBB);
+}
+
 Instruction *Instruction::cloneImpl() const {
   llvm_unreachable("Subclass of Instruction failed to implement cloneImpl");
 }