[NFC][ValueTracking] Add OffsetZero into findAllocaForValue

For StackLifetime after finding alloca we need to check that
values ponting to the begining of alloca.

Reviewed By: eugenis

Differential Revision: https://reviews.llvm.org/D86692

llvm/include/llvm/Analysis/ValueTracking.h

@@ -413,10 +413,12 @@ constexpr unsigned MaxAnalysisRecursionDepth = 6;
   bool getUnderlyingObjectsForCodeGen(const Value *V,
                                       SmallVectorImpl<Value *> &Objects);
 
-  /// Finds alloca where the value comes from.
-  AllocaInst *findAllocaForValue(Value *V);
-  inline const AllocaInst *findAllocaForValue(const Value *V) {
-    return findAllocaForValue(const_cast<Value *>(V));
+  /// Returns unique alloca where the value comes from, or nullptr.
+  /// If OffsetZero is true check that V points to the begining of the alloca.
+  AllocaInst *findAllocaForValue(Value *V, bool OffsetZero = false);
+  inline const AllocaInst *findAllocaForValue(const Value *V,
+                                              bool OffsetZero = false) {
+    return findAllocaForValue(const_cast<Value *>(V), OffsetZero);
   }
 
   /// Return true if the only users of this pointer are lifetime markers.

llvm/lib/Analysis/ValueTracking.cpp

@@ -4331,7 +4331,8 @@ bool llvm::getUnderlyingObjectsForCodeGen(const Value *V,
 }
 
 static AllocaInst *
-findAllocaForValue(Value *V, DenseMap<Value *, AllocaInst *> &AllocaForValue) {
+findAllocaForValue(Value *V, DenseMap<Value *, AllocaInst *> &AllocaForValue,
+                   bool OffsetZero) {
   if (AllocaInst *AI = dyn_cast<AllocaInst>(V))
     return AI;
   // See if we've already calculated (or started to calculate) alloca for a
@@ -4344,36 +4345,41 @@ findAllocaForValue(Value *V, DenseMap<Value *, AllocaInst *> &AllocaForValue) {
   AllocaForValue[V] = nullptr;
   AllocaInst *Res = nullptr;
   if (CastInst *CI = dyn_cast<CastInst>(V))
-    Res = findAllocaForValue(CI->getOperand(0), AllocaForValue);
-  else if (auto *SI = dyn_cast<SelectInst>(V)) {
-    Res = findAllocaForValue(SI->getTrueValue(), AllocaForValue);
-    if (!Res)
-      return nullptr;
-    AllocaInst *F = findAllocaForValue(SI->getFalseValue(), AllocaForValue);
-    if (F != Res)
-      return nullptr;
-  } else if (PHINode *PN = dyn_cast<PHINode>(V)) {
+    Res = findAllocaForValue(CI->getOperand(0), AllocaForValue, OffsetZero);
+  else if (PHINode *PN = dyn_cast<PHINode>(V)) {
     for (Value *IncValue : PN->incoming_values()) {
       // Allow self-referencing phi-nodes.
       if (IncValue == PN)
         continue;
-      AllocaInst *IncValueAI = findAllocaForValue(IncValue, AllocaForValue);
+      AllocaInst *IncValueAI =
+          findAllocaForValue(IncValue, AllocaForValue, OffsetZero);
       // AI for incoming values should exist and should all be equal.
       if (IncValueAI == nullptr || (Res != nullptr && IncValueAI != Res))
         return nullptr;
       Res = IncValueAI;
     }
-  } else if (GetElementPtrInst *EP = dyn_cast<GetElementPtrInst>(V)) {
-    Res = findAllocaForValue(EP->getPointerOperand(), AllocaForValue);
+  } else if (auto *SI = dyn_cast<SelectInst>(V)) {
+    Res = findAllocaForValue(SI->getTrueValue(), AllocaForValue, OffsetZero);
+    if (!Res)
+      return nullptr;
+    AllocaInst *F =
+        findAllocaForValue(SI->getFalseValue(), AllocaForValue, OffsetZero);
+    if (F != Res)
+      return nullptr;
+  } else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(V)) {
+    if (OffsetZero && !GEP->hasAllZeroIndices())
+      return nullptr;
+    Res = findAllocaForValue(GEP->getPointerOperand(), AllocaForValue,
+                             OffsetZero);
   }
   if (Res)
     AllocaForValue[V] = Res;
   return Res;
 }
 
-AllocaInst *llvm::findAllocaForValue(Value *V) {
+AllocaInst *llvm::findAllocaForValue(Value *V, bool OffsetZero) {
   DenseMap<Value *, AllocaInst *> AllocaForValue;
-  return ::findAllocaForValue(V, AllocaForValue);
+  return ::findAllocaForValue(V, AllocaForValue, OffsetZero);
 }
 
 static bool onlyUsedByLifetimeMarkersOrDroppableInstsHelper(

llvm/unittests/Analysis/ValueTrackingTest.cpp

@@ -1433,7 +1433,8 @@ TEST_F(ValueTrackingTest, ComputeConstantRange) {
 
 struct FindAllocaForValueTestParams {
   const char *IR;
-  bool Result;
+  bool AnyOffsetResult;
+  bool ZeroOffsetResult;
 };
 
 class FindAllocaForValueTest
@@ -1449,15 +1450,23 @@ const FindAllocaForValueTestParams FindAllocaForValueTests[] = {
         %r = bitcast i64* %a to i32*
         ret void
       })",
-     true},
+     true, true},
 
     {R"(
       define void @test() {
         %a = alloca i32
         %r = getelementptr i32, i32* %a, i32 1
         ret void
       })",
-     true},
+     true, false},
+
+    {R"(
+      define void @test() {
+        %a = alloca i32
+        %r = getelementptr i32, i32* %a, i32 0
+        ret void
+      })",
+     true, true},
 
     {R"(
       define void @test(i1 %cond) {
@@ -1472,15 +1481,15 @@ const FindAllocaForValueTestParams FindAllocaForValueTests[] = {
       exit:
         ret void
       })",
-     true},
+     true, true},
 
     {R"(
       define void @test(i1 %cond) {
         %a = alloca i32
         %r = select i1 %cond, i32* %a, i32* %a
         ret void
       })",
-     true},
+     true, true},
 
     {R"(
       define void @test(i1 %cond) {
@@ -1489,7 +1498,7 @@ const FindAllocaForValueTestParams FindAllocaForValueTests[] = {
         %r = select i1 %cond, i32* %a, i32* %b
         ret void
       })",
-     false},
+     false, false},
 
     {R"(
       define void @test(i1 %cond) {
@@ -1506,7 +1515,7 @@ const FindAllocaForValueTestParams FindAllocaForValueTests[] = {
       exit:
         ret void
       })",
-     true},
+     true, false},
 
     {R"(
       define void @test(i1 %cond) {
@@ -1523,15 +1532,15 @@ const FindAllocaForValueTestParams FindAllocaForValueTests[] = {
       exit:
         ret void
       })",
-     false},
+     false, false},
 
     {R"(
       define void @test(i1 %cond, i64* %a) {
       entry:
         %r = bitcast i64* %a to i32*
         ret void
       })",
-     false},
+     false, false},
 
     {R"(
       define void @test(i1 %cond) {
@@ -1547,15 +1556,23 @@ const FindAllocaForValueTestParams FindAllocaForValueTests[] = {
       exit:
         ret void
       })",
-     false},
+     false, false},
 };
 
 TEST_P(FindAllocaForValueTest, findAllocaForValue) {
   auto M = parseModule(GetParam().IR);
   Function *F = M->getFunction("test");
   Instruction *I = &findInstructionByName(F, "r");
   const AllocaInst *AI = findAllocaForValue(I);
-  EXPECT_EQ(!!AI, GetParam().Result);
+  EXPECT_EQ(!!AI, GetParam().AnyOffsetResult);
+}
+
+TEST_P(FindAllocaForValueTest, findAllocaForValueZeroOffset) {
+  auto M = parseModule(GetParam().IR);
+  Function *F = M->getFunction("test");
+  Instruction *I = &findInstructionByName(F, "r");
+  const AllocaInst *AI = findAllocaForValue(I, true);
+  EXPECT_EQ(!!AI, GetParam().ZeroOffsetResult);
 }
 
 INSTANTIATE_TEST_CASE_P(FindAllocaForValueTest, FindAllocaForValueTest,