[SandboxVec][VecUtils] Implement VecUtils::getLowest() (#124024)

VecUtils::getLowest(Valse) returns the lowest instruction in the BB among Vals.
If the instructions are not in the same BB, or if none of them is an
instruction it returns nullptr.

Author: vporpo

llvm/include/llvm/Transforms/Vectorize/SandboxVectorizer/VecUtils.h

@@ -100,6 +100,8 @@ class VecUtils {
     }
     return FixedVectorType::get(ElemTy, NumElts);
   }
+  /// \Returns the instruction in \p Instrs that is lowest in the BB. Expects
+  /// that all instructions are in the same BB.
   static Instruction *getLowest(ArrayRef<Instruction *> Instrs) {
     Instruction *LowestI = Instrs.front();
     for (auto *I : drop_begin(Instrs)) {
@@ -108,6 +110,33 @@ class VecUtils {
     }
     return LowestI;
   }
+  /// \Returns the lowest instruction in \p Vals, or nullptr if no instructions
+  /// are found or if not in the same BB.
+  static Instruction *getLowest(ArrayRef<Value *> Vals) {
+    // Find the first Instruction in Vals.
+    auto It = find_if(Vals, [](Value *V) { return isa<Instruction>(V); });
+    // If we couldn't find an instruction return nullptr.
+    if (It == Vals.end())
+      return nullptr;
+    Instruction *FirstI = cast<Instruction>(*It);
+    // Now look for the lowest instruction in Vals starting from one position
+    // after FirstI.
+    Instruction *LowestI = FirstI;
+    auto *LowestBB = LowestI->getParent();
+    for (auto *V : make_range(std::next(It), Vals.end())) {
+      auto *I = dyn_cast<Instruction>(V);
+      // Skip non-instructions.
+      if (I == nullptr)
+        continue;
+      // If the instructions are in different BBs return nullptr.
+      if (I->getParent() != LowestBB)
+        return nullptr;
+      // If `LowestI` comes before `I` then `I` is the new lowest.
+      if (LowestI->comesBefore(I))
+        LowestI = I;
+    }
+    return LowestI;
+  }
   /// If all values in \p Bndl are of the same scalar type then return it,
   /// otherwise return nullptr.
   static Type *tryGetCommonScalarType(ArrayRef<Value *> Bndl) {

llvm/lib/Transforms/Vectorize/SandboxVectorizer/Passes/BottomUpVec.cpp

@@ -45,11 +45,7 @@ static SmallVector<Value *, 4> getOperand(ArrayRef<Value *> Bndl,
 
 static BasicBlock::iterator
 getInsertPointAfterInstrs(ArrayRef<Value *> Instrs) {
-  // TODO: Use the VecUtils function for getting the bottom instr once it lands.
-  auto *BotI = cast<Instruction>(
-      *std::max_element(Instrs.begin(), Instrs.end(), [](auto *V1, auto *V2) {
-        return cast<Instruction>(V1)->comesBefore(cast<Instruction>(V2));
-      }));
+  auto *BotI = VecUtils::getLowest(Instrs);
   // If Bndl contains Arguments or Constants, use the beginning of the BB.
   return std::next(BotI->getIterator());
 }

llvm/unittests/Transforms/Vectorize/SandboxVectorizer/VecUtilsTest.cpp

@@ -50,6 +50,14 @@ struct VecUtilsTest : public testing::Test {
   }
 };
 
+sandboxir::BasicBlock &getBasicBlockByName(sandboxir::Function &F,
+                                           StringRef Name) {
+  for (sandboxir::BasicBlock &BB : F)
+    if (BB.getName() == Name)
+      return BB;
+  llvm_unreachable("Expected to find basic block!");
+}
+
 TEST_F(VecUtilsTest, GetNumElements) {
   sandboxir::Context Ctx(C);
   auto *ElemTy = sandboxir::Type::getInt32Ty(Ctx);
@@ -415,21 +423,33 @@ TEST_F(VecUtilsTest, GetLowest) {
   parseIR(R"IR(
 define void @foo(i8 %v) {
 bb0:
-  %A = add i8 %v, %v
-  %B = add i8 %v, %v
-  %C = add i8 %v, %v
+  br label %bb1
+bb1:
+  %A = add i8 %v, 1
+  %B = add i8 %v, 2
+  %C = add i8 %v, 3
   ret void
 }
 )IR");
   Function &LLVMF = *M->getFunction("foo");
 
   sandboxir::Context Ctx(C);
   auto &F = *Ctx.createFunction(&LLVMF);
-  auto &BB = *F.begin();
-  auto It = BB.begin();
-  auto *IA = &*It++;
-  auto *IB = &*It++;
-  auto *IC = &*It++;
+  auto &BB0 = getBasicBlockByName(F, "bb0");
+  auto It = BB0.begin();
+  auto *BB0I = cast<sandboxir::BranchInst>(&*It++);
+
+  auto &BB = getBasicBlockByName(F, "bb1");
+  It = BB.begin();
+  auto *IA = cast<sandboxir::Instruction>(&*It++);
+  auto *C1 = cast<sandboxir::Constant>(IA->getOperand(1));
+  auto *IB = cast<sandboxir::Instruction>(&*It++);
+  auto *C2 = cast<sandboxir::Constant>(IB->getOperand(1));
+  auto *IC = cast<sandboxir::Instruction>(&*It++);
+  auto *C3 = cast<sandboxir::Constant>(IC->getOperand(1));
+  // Check getLowest(ArrayRef<Instruction *>)
+  SmallVector<sandboxir::Instruction *> A({IA});
+  EXPECT_EQ(sandboxir::VecUtils::getLowest(A), IA);
   SmallVector<sandboxir::Instruction *> ABC({IA, IB, IC});
   EXPECT_EQ(sandboxir::VecUtils::getLowest(ABC), IC);
   SmallVector<sandboxir::Instruction *> ACB({IA, IC, IB});
@@ -438,6 +458,27 @@ define void @foo(i8 %v) {
   EXPECT_EQ(sandboxir::VecUtils::getLowest(CAB), IC);
   SmallVector<sandboxir::Instruction *> CBA({IC, IB, IA});
   EXPECT_EQ(sandboxir::VecUtils::getLowest(CBA), IC);
+
+  // Check getLowest(ArrayRef<Value *>)
+  SmallVector<sandboxir::Value *> C1Only({C1});
+  EXPECT_EQ(sandboxir::VecUtils::getLowest(C1Only), nullptr);
+  SmallVector<sandboxir::Value *> AOnly({IA});
+  EXPECT_EQ(sandboxir::VecUtils::getLowest(AOnly), IA);
+  SmallVector<sandboxir::Value *> AC1({IA, C1});
+  EXPECT_EQ(sandboxir::VecUtils::getLowest(AC1), IA);
+  SmallVector<sandboxir::Value *> C1A({C1, IA});
+  EXPECT_EQ(sandboxir::VecUtils::getLowest(C1A), IA);
+  SmallVector<sandboxir::Value *> AC1B({IA, C1, IB});
+  EXPECT_EQ(sandboxir::VecUtils::getLowest(AC1B), IB);
+  SmallVector<sandboxir::Value *> ABC1({IA, IB, C1});
+  EXPECT_EQ(sandboxir::VecUtils::getLowest(ABC1), IB);
+  SmallVector<sandboxir::Value *> AC1C2({IA, C1, C2});
+  EXPECT_EQ(sandboxir::VecUtils::getLowest(AC1C2), IA);
+  SmallVector<sandboxir::Value *> C1C2C3({C1, C2, C3});
+  EXPECT_EQ(sandboxir::VecUtils::getLowest(C1C2C3), nullptr);
+
+  SmallVector<sandboxir::Value *> DiffBBs({BB0I, IA});
+  EXPECT_EQ(sandboxir::VecUtils::getLowest(DiffBBs), nullptr);
 }
 
 TEST_F(VecUtilsTest, GetCommonScalarType) {