[CodeMoverUtils] Enhance CodeMoverUtils to sink an entire BB

llvm/lib/Transforms/Utils/CodeMoverUtils.cpp

@@ -336,9 +336,22 @@ bool llvm::isSafeToMoveBefore(Instruction &I, Instruction &InsertPoint,
 
   if (isReachedBefore(&I, &InsertPoint, &DT, PDT))
     for (const Use &U : I.uses())
-      if (auto *UserInst = dyn_cast<Instruction>(U.getUser()))
-        if (UserInst != &InsertPoint && !DT.dominates(&InsertPoint, U))
+      if (auto *UserInst = dyn_cast<Instruction>(U.getUser())) {
+        // If InsertPoint is in a BB that comes after I, then we cannot move if
+        // I is used in the terminator of the current BB.
+        if (I.getParent() == InsertPoint.getParent() &&
+            UserInst == I.getParent()->getTerminator())
           return false;
+        if (UserInst != &InsertPoint && !DT.dominates(&InsertPoint, U)) {
+          // If UserInst is an instruction that appears later in the same BB as
+          // I, then it is okay to move since I will still be available when
+          // UserInst is executed.
+          if (CheckForEntireBlock && I.getParent() == UserInst->getParent() &&
+              DT.dominates(&I, UserInst))
+            continue;
+          return false;
+        }
+      }
   if (isReachedBefore(&InsertPoint, &I, &DT, PDT))
     for (const Value *Op : I.operands())
       if (auto *OpInst = dyn_cast<Instruction>(Op)) {

llvm/unittests/Transforms/Utils/CodeMoverUtilsTest.cpp

@@ -673,6 +673,11 @@ TEST(CodeMoverUtils, IsSafeToMoveTest4) {
         // Can move as %add2 and %sub2 are control flow equivalent,
         // although %add2 does not strictly dominate %sub2.
         EXPECT_TRUE(isSafeToMoveBefore(*SubInst2, *AddInst2, DT, &PDT, &DI));
+
+        BasicBlock *BB0 = getBasicBlockByName(F, "if.then.first");
+        BasicBlock *BB1 = getBasicBlockByName(F, "if.then.second");
+        EXPECT_TRUE(
+            isSafeToMoveBefore(*BB0, *BB1->getTerminator(), DT, &PDT, &DI));
       });
 }