5 files changed, 112 insertions, 5 deletions
diff --git a/llvm/include/llvm/Analysis/AliasSetTracker.h b/llvm/include/llvm/Analysis/AliasSetTracker.h
index 6dcd4a0441f..403a2b586f6 100644
--- a/llvm/include/llvm/Analysis/AliasSetTracker.h
+++ b/llvm/include/llvm/Analysis/AliasSetTracker.h
@@ -370,6 +370,10 @@ public:
   /// alias sets.
   bool containsPointer(Value *P, uint64_t Size, const AAMDNodes &AAInfo) const;
 
+  /// Return true if the specified instruction "may" (or must) alias one of the
+  /// members in any of the sets.
+  bool containsUnknown(Instruction *I) const;
+
   /// getAliasAnalysis - Return the underlying alias analysis object used by
   /// this tracker.
   AliasAnalysis &getAliasAnalysis() const { return AA; }
diff --git a/llvm/lib/Analysis/AliasSetTracker.cpp b/llvm/lib/Analysis/AliasSetTracker.cpp
index 843a5413209..9d941e55797 100644
--- a/llvm/lib/Analysis/AliasSetTracker.cpp
+++ b/llvm/lib/Analysis/AliasSetTracker.cpp
@@ -242,7 +242,12 @@ bool AliasSetTracker::containsPointer(Value *Ptr, uint64_t Size,
   return false;
 }
 
-
+bool AliasSetTracker::containsUnknown(Instruction *Inst) const {
+  for (const_iterator I = begin(), E = end(); I != E; ++I)
+    if (!I->Forward && I->aliasesUnknownInst(Inst, AA))
+      return true;
+  return false;
+}
 
 AliasSet *AliasSetTracker::findAliasSetForUnknownInst(Instruction *Inst) {
   AliasSet *FoundSet = nullptr;
diff --git a/llvm/lib/Transforms/Scalar/LoadCombine.cpp b/llvm/lib/Transforms/Scalar/LoadCombine.cpp
index 648626a7c12..11e4d7606d9 100644
--- a/llvm/lib/Transforms/Scalar/LoadCombine.cpp
+++ b/llvm/lib/Transforms/Scalar/LoadCombine.cpp
@@ -15,6 +15,8 @@
 
 #include "llvm/ADT/DenseMap.h"
 #include "llvm/ADT/Statistic.h"
+#include "llvm/Analysis/AliasAnalysis.h"
+#include "llvm/Analysis/AliasSetTracker.h"
 #include "llvm/Analysis/TargetFolder.h"
 #include "llvm/Pass.h"
 #include "llvm/IR/DataLayout.h"
@@ -51,11 +53,12 @@ struct LoadPOPPair {
 class LoadCombine : public BasicBlockPass {
   LLVMContext *C;
   const DataLayout *DL;
+  AliasAnalysis *AA;
 
 public:
   LoadCombine()
       : BasicBlockPass(ID),
-        C(nullptr), DL(nullptr) {
+        C(nullptr), DL(nullptr), AA(nullptr) {
     initializeSROAPass(*PassRegistry::getPassRegistry());
   }
   
@@ -225,19 +228,23 @@ bool LoadCombine::runOnBasicBlock(BasicBlock &BB) {
   if (skipOptnoneFunction(BB) || !DL)
     return false;
 
+  AA = &getAnalysis<AliasAnalysis>();
+
   IRBuilder<true, TargetFolder>
   TheBuilder(BB.getContext(), TargetFolder(DL));
   Builder = &TheBuilder;
 
   DenseMap<const Value *, SmallVector<LoadPOPPair, 8>> LoadMap;
+  AliasSetTracker AST(*AA);
 
   bool Combined = false;
   unsigned Index = 0;
   for (auto &I : BB) {
-    if (I.mayWriteToMemory() || I.mayThrow()) {
+    if (I.mayThrow() || (I.mayWriteToMemory() && AST.containsUnknown(&I))) {
       if (combineLoads(LoadMap))
         Combined = true;
       LoadMap.clear();
+      AST.clear();
       continue;
     }
     LoadInst *LI = dyn_cast<LoadInst>(&I);
@@ -250,6 +257,7 @@ bool LoadCombine::runOnBasicBlock(BasicBlock &BB) {
     if (!POP.Pointer)
       continue;
     LoadMap[POP.Pointer].push_back(LoadPOPPair(LI, POP, Index++));
+    AST.add(LI);
   }
   if (combineLoads(LoadMap))
     Combined = true;
@@ -258,6 +266,9 @@ bool LoadCombine::runOnBasicBlock(BasicBlock &BB) {
 
 void LoadCombine::getAnalysisUsage(AnalysisUsage &AU) const {
   AU.setPreservesCFG();
+
+  AU.addRequired<AliasAnalysis>();
+  AU.addPreserved<AliasAnalysis>();
 }
 
 char LoadCombine::ID = 0;
@@ -266,5 +277,9 @@ BasicBlockPass *llvm::createLoadCombinePass() {
   return new LoadCombine();
 }
 
-INITIALIZE_PASS(LoadCombine, "load-combine", "Combine Adjacent Loads", false,
-                false)
+INITIALIZE_PASS_BEGIN(LoadCombine, "load-combine", "Combine Adjacent Loads",
+                      false, false)
+INITIALIZE_AG_DEPENDENCY(AliasAnalysis)
+INITIALIZE_PASS_END(LoadCombine, "load-combine", "Combine Adjacent Loads",
+                    false, false)
+
diff --git a/llvm/test/Transforms/LoadCombine/load-combine-aa.ll b/llvm/test/Transforms/LoadCombine/load-combine-aa.ll
new file mode 100644
index 00000000000..3542dcebf5e
--- /dev/null
+++ b/llvm/test/Transforms/LoadCombine/load-combine-aa.ll
@@ -0,0 +1,39 @@
+; RUN: opt -basicaa -load-combine -instcombine -S < %s | FileCheck %s
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+define i64 @test1(i32* nocapture readonly noalias %a, i32* nocapture readonly noalias %b) {
+; CHECK-LABEL: @test1
+
+; CHECK: load i64*
+; CHECK: ret i64
+
+  %load1 = load i32* %a, align 4
+  %conv = zext i32 %load1 to i64
+  %arrayidx1 = getelementptr inbounds i32* %a, i64 1
+  store i32 %load1, i32* %b, align 4
+  %load2 = load i32* %arrayidx1, align 4
+  %conv2 = zext i32 %load2 to i64
+  %shl = shl nuw i64 %conv2, 32
+  %add = or i64 %shl, %conv
+  ret i64 %add
+}
+
+define i64 @test2(i32* nocapture readonly %a, i32* nocapture readonly %b) {
+; CHECK-LABEL: @test2
+
+; CHECK: load i32*
+; CHECK: load i32*
+; CHECK: ret i64
+
+  %load1 = load i32* %a, align 4
+  %conv = zext i32 %load1 to i64
+  %arrayidx1 = getelementptr inbounds i32* %a, i64 1
+  store i32 %load1, i32* %b, align 4
+  %load2 = load i32* %arrayidx1, align 4
+  %conv2 = zext i32 %load2 to i64
+  %shl = shl nuw i64 %conv2, 32
+  %add = or i64 %shl, %conv
+  ret i64 %add
+}
+
diff --git a/llvm/test/Transforms/LoadCombine/load-combine-assume.ll b/llvm/test/Transforms/LoadCombine/load-combine-assume.ll
new file mode 100644
index 00000000000..94f630072ad
--- /dev/null
+++ b/llvm/test/Transforms/LoadCombine/load-combine-assume.ll
@@ -0,0 +1,44 @@
+; RUN: opt -basicaa -load-combine -instcombine -S < %s | FileCheck %s
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+declare void @llvm.assume(i1) nounwind
+
+; 'load' before the 'call' gets optimized:
+define i64 @test1(i32* nocapture readonly %a, i1 %b) {
+; CHECK-LABEL: @test1
+
+; CHECK-DAG: load i64* %1, align 4
+; CHECK-DAG: tail call void @llvm.assume(i1 %b)
+; CHECK: ret i64
+
+  %load1 = load i32* %a, align 4
+  %conv = zext i32 %load1 to i64
+  %arrayidx1 = getelementptr inbounds i32* %a, i64 1
+  %load2 = load i32* %arrayidx1, align 4
+  tail call void @llvm.assume(i1 %b)
+  %conv2 = zext i32 %load2 to i64
+  %shl = shl nuw i64 %conv2, 32
+  %add = or i64 %shl, %conv
+  ret i64 %add
+}
+
+; 'call' before the 'load' doesn't get optimized:
+define i64 @test2(i32* nocapture readonly %a, i1 %b) {
+; CHECK-LABEL: @test2
+
+; CHECK-DAG: load i64* %1, align 4
+; CHECK-DAG: tail call void @llvm.assume(i1 %b)
+; CHECK: ret i64
+
+  %load1 = load i32* %a, align 4
+  %conv = zext i32 %load1 to i64
+  %arrayidx1 = getelementptr inbounds i32* %a, i64 1
+  tail call void @llvm.assume(i1 %b)
+  %load2 = load i32* %arrayidx1, align 4
+  %conv2 = zext i32 %load2 to i64
+  %shl = shl nuw i64 %conv2, 32
+  %add = or i64 %shl, %conv
+  ret i64 %add
+}
+