[SandboxIR] Implement missng Instruction::comesBefore()

llvm/include/llvm/SandboxIR/SandboxIR.h

@@ -1558,6 +1558,14 @@ class Instruction : public sandboxir::User {
   void moveAfter(Instruction *After) {
     moveBefore(*After->getParent(), std::next(After->getIterator()));
   }
+  // TODO: This currently relies on LLVM IR Instruction::comesBefore which is
+  // can be linear-time.
+  /// Given an instruction Other in the same basic block as this instruction,
+  /// return true if this instruction comes before Other.
+  bool comesBefore(const Instruction *Other) const {
+    return cast<llvm::Instruction>(Val)->comesBefore(
+        cast<llvm::Instruction>(Other->Val));
+  }
   /// \Returns the BasicBlock containing this Instruction, or null if it is
   /// detached.
   BasicBlock *getParent() const;

llvm/unittests/SandboxIR/SandboxIRTest.cpp

@@ -1366,6 +1366,10 @@ define void @foo(i8 %v1) {
   EXPECT_EQ(I0->getNextNode(), I1);
   EXPECT_EQ(I1->getPrevNode(), I0);
 
+  // Check comesBefore(I).
+  EXPECT_TRUE(I0->comesBefore(I1));
+  EXPECT_FALSE(I1->comesBefore(I0));
+
   // Check moveBefore(BB, It).
   I1->moveBefore(*BB, BB->begin());
   EXPECT_EQ(I1->getPrevNode(), nullptr);