BasicAA should look through functions with returned arguments

Motivated by the work on the llvm.noalias intrinsic, teach BasicAA to look
through returned-argument functions when answering queries. This is essential
so that we don't loose all other AA information when supplementing with
llvm.noalias.

Differential Revision: http://reviews.llvm.org/D9383

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@275035 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Analysis/BasicAliasAnalysis.cpp

@@ -376,6 +376,12 @@ bool BasicAAResult::DecomposeGEPExpression(const Value *V,
 
     const GEPOperator *GEPOp = dyn_cast<GEPOperator>(Op);
     if (!GEPOp) {
+      if (auto CS = ImmutableCallSite(V))
+        if (const Value *RV = CS.getReturnedArgOperand()) {
+          V = RV;
+          continue;
+        }
+
       // If it's not a GEP, hand it off to SimplifyInstruction to see if it
       // can come up with something. This matches what GetUnderlyingObject does.
       if (const Instruction *I = dyn_cast<Instruction>(V))
@@ -817,7 +823,10 @@ static AliasResult aliasSameBasePointerGEPs(const GEPOperator *GEP1,
                                             uint64_t V2Size,
                                             const DataLayout &DL) {
 
-  assert(GEP1->getPointerOperand() == GEP2->getPointerOperand() &&
+  assert(GEP1->getPointerOperand()->stripPointerCasts() ==
+         GEP2->getPointerOperand()->stripPointerCasts() &&
+         GEP1->getPointerOperand()->getType() ==
+         GEP2->getPointerOperand()->getType() &&
          "Expected GEPs with the same pointer operand");
 
   // Try to determine whether GEP1 and GEP2 index through arrays, into structs,
@@ -1075,7 +1084,10 @@ AliasResult BasicAAResult::aliasGEP(const GEPOperator *GEP1, uint64_t V1Size,
     // If we know the two GEPs are based off of the exact same pointer (and not
     // just the same underlying object), see if that tells us anything about
     // the resulting pointers.
-    if (GEP1->getPointerOperand() == GEP2->getPointerOperand()) {
+    if (GEP1->getPointerOperand()->stripPointerCasts() ==
+        GEP2->getPointerOperand()->stripPointerCasts() &&
+        GEP1->getPointerOperand()->getType() ==
+        GEP2->getPointerOperand()->getType()) {
       AliasResult R = aliasSameBasePointerGEPs(GEP1, V1Size, GEP2, V2Size, DL);
       // If we couldn't find anything interesting, don't abandon just yet.
       if (R != MayAlias)

lib/Analysis/ValueTracking.cpp

@@ -2981,6 +2981,12 @@ Value *llvm::GetUnderlyingObject(Value *V, const DataLayout &DL,
         return V;
       V = GA->getAliasee();
     } else {
+      if (auto CS = CallSite(V))
+        if (Value *RV = CS.getReturnedArgOperand()) {
+          V = RV;
+          continue;
+        }
+
       // See if InstructionSimplify knows any relevant tricks.
       if (Instruction *I = dyn_cast<Instruction>(V))
         // TODO: Acquire a DominatorTree and AssumptionCache and use them.

lib/IR/Value.cpp

@@ -464,6 +464,12 @@ static Value *stripPointerCastsAndOffsets(Value *V) {
         return V;
       V = GA->getAliasee();
     } else {
+      if (auto CS = CallSite(V))
+        if (Value *RV = CS.getReturnedArgOperand()) {
+          V = RV;
+          continue;
+        }
+
       return V;
     }
     assert(V->getType()->isPointerTy() && "Unexpected operand type!");
@@ -513,6 +519,12 @@ Value *Value::stripAndAccumulateInBoundsConstantOffsets(const DataLayout &DL,
     } else if (GlobalAlias *GA = dyn_cast<GlobalAlias>(V)) {
       V = GA->getAliasee();
     } else {
+      if (auto CS = CallSite(V))
+        if (Value *RV = CS.getReturnedArgOperand()) {
+          V = RV;
+          continue;
+        }
+
       return V;
     }
     assert(V->getType()->isPointerTy() && "Unexpected operand type!");

test/Analysis/BasicAA/returned.ll

@@ -0,0 +1,45 @@
+; RUN: opt < %s -basicaa -aa-eval -print-all-alias-modref-info -disable-output 2>&1 | FileCheck %s
+
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+
+%struct = type { i32, i32, i32 }
+
+; CHECK-LABEL: test_simple
+
+; CHECK-DAG: MustAlias: %struct* %st, %struct* %sta
+
+; CHECK-DAG: PartialAlias: %struct* %st, i32* %x
+; CHECK-DAG: PartialAlias: %struct* %st, i32* %y
+; CHECK-DAG: PartialAlias: %struct* %st, i32* %z
+
+; CHECK-DAG: NoAlias: i32* %x, i32* %y
+; CHECK-DAG: NoAlias: i32* %x, i32* %z
+; CHECK-DAG: NoAlias: i32* %y, i32* %z
+
+; CHECK-DAG: PartialAlias: %struct* %st, %struct* %y_12
+; CHECK-DAG: PartialAlias: %struct* %y_12, i32* %x
+; CHECK-DAG: PartialAlias: i32* %x, i80* %y_10
+
+; CHECK-DAG: PartialAlias: %struct* %st, i64* %y_8
+; CHECK-DAG: PartialAlias: i32* %z, i64* %y_8
+; CHECK-DAG: NoAlias: i32* %x, i64* %y_8
+
+; CHECK-DAG: MustAlias: %struct* %y_12, i32* %y
+; CHECK-DAG: MustAlias: i32* %y, i64* %y_8
+; CHECK-DAG: MustAlias: i32* %y, i80* %y_10
+
+define void @test_simple(%struct* %st, i64 %i, i64 %j, i64 %k) {
+  %x = getelementptr %struct, %struct* %st, i64 %i, i32 0
+  %y = getelementptr %struct, %struct* %st, i64 %j, i32 1
+  %sta = call %struct* @func2(%struct* %st)
+  %z = getelementptr %struct, %struct* %sta, i64 %k, i32 2
+  %y_12 = bitcast i32* %y to %struct*
+  %y_10 = bitcast i32* %y to i80*
+  %ya = call i32* @func1(i32* %y)
+  %y_8 = bitcast i32* %ya to i64*
+  ret void
+}
+
+declare i32* @func1(i32* returned) nounwind
+declare %struct* @func2(%struct* returned) nounwind
+