BasicAliasAnalysis and FunctionAttrs were both
doing very similar pointer capture analysis.
Factor out the common logic. The new version
is from FunctionAttrs since it does a better
job than the version in BasicAliasAnalysis
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@62461 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Analysis/BasicAliasAnalysis.cpp b/lib/Analysis/BasicAliasAnalysis.cpp
index 9cefdcf..8251440 100644
--- a/lib/Analysis/BasicAliasAnalysis.cpp
+++ b/lib/Analysis/BasicAliasAnalysis.cpp
@@ -14,6 +14,7 @@
//===----------------------------------------------------------------------===//
#include "llvm/Analysis/AliasAnalysis.h"
+#include "llvm/Analysis/CaptureTracking.h"
#include "llvm/Analysis/Passes.h"
#include "llvm/Constants.h"
#include "llvm/DerivedTypes.h"
@@ -35,56 +36,6 @@
// Useful predicates
//===----------------------------------------------------------------------===//
-// Determine if a value escapes from the function it is contained in (being
-// returned by the function does not count as escaping here). If a value local
-// to the function does not escape, there is no way another function can mod/ref
-// it. We do this by looking at its uses and determining if they can escape
-// (recursively).
-static bool AddressMightEscape(const Value *V) {
- for (Value::use_const_iterator UI = V->use_begin(), E = V->use_end();
- UI != E; ++UI) {
- const Instruction *I = cast<Instruction>(*UI);
- switch (I->getOpcode()) {
- case Instruction::Load:
- break; //next use.
- case Instruction::Store:
- if (I->getOperand(0) == V)
- return true; // Escapes if the pointer is stored.
- break; // next use.
- case Instruction::GetElementPtr:
- if (AddressMightEscape(I))
- return true;
- break; // next use.
- case Instruction::BitCast:
- if (AddressMightEscape(I))
- return true;
- break; // next use
- case Instruction::Ret:
- // If returned, the address will escape to calling functions, but no
- // callees could modify it.
- break; // next use
- case Instruction::Call:
- // If the argument to the call has the nocapture attribute, then the call
- // may store or load to the pointer, but it cannot escape.
- if (cast<CallInst>(I)->paramHasAttr(UI.getOperandNo(),
- Attribute::NoCapture))
- continue;
- return true;
- case Instruction::Invoke:
- // If the argument to the call has the nocapture attribute, then the call
- // may store or load to the pointer, but it cannot escape.
- // Do compensate for the two BB operands, i.e. Arg1 is at index 3!
- if (cast<InvokeInst>(I)->paramHasAttr(UI.getOperandNo()-2,
- Attribute::NoCapture))
- continue;
- return true;
- default:
- return true;
- }
- }
- return false;
-}
-
static const User *isGEP(const Value *V) {
if (isa<GetElementPtrInst>(V) ||
(isa<ConstantExpr>(V) &&
@@ -158,7 +109,7 @@
static bool isNonEscapingLocalObject(const Value *V) {
// If this is a local allocation, check to see if it escapes.
if (isa<AllocationInst>(V) || isNoAliasCall(V))
- return !AddressMightEscape(V);
+ return !PointerMayBeCaptured(V, false);
// If this is an argument that corresponds to a byval or noalias argument,
// then it has not escaped before entering the function. Check if it escapes
@@ -168,7 +119,7 @@
// Don't bother analyzing arguments already known not to escape.
if (A->hasNoCaptureAttr())
return true;
- return !AddressMightEscape(V);
+ return !PointerMayBeCaptured(V, false);
}
return false;
}
diff --git a/lib/Analysis/CaptureTracking.cpp b/lib/Analysis/CaptureTracking.cpp
new file mode 100644
index 0000000..ceb9646
--- /dev/null
+++ b/lib/Analysis/CaptureTracking.cpp
@@ -0,0 +1,110 @@
+//===--- CaptureTracking.cpp - Determine whether a pointer is captured ----===//
+//
+// The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file contains routines that help determine which pointers are captured.
+// A pointer value is captured if the function makes a copy of any part of the
+// pointer that outlives the call. Not being captured means, more or less, that
+// the pointer is only dereferenced and not stored in a global. Returning part
+// of the pointer as the function return value may or may not count as capturing
+// the pointer, depending on the context.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Analysis/CaptureTracking.h"
+#include "llvm/Instructions.h"
+#include "llvm/Value.h"
+#include "llvm/ADT/SmallSet.h"
+#include "llvm/ADT/SmallVector.h"
+#include "llvm/Support/CallSite.h"
+using namespace llvm;
+
+/// PointerMayBeCaptured - Return true if this pointer value may be captured
+/// by the enclosing function (which is required to exist). This routine can
+/// be expensive, so consider caching the results. The boolean ReturnCaptures
+/// specifies whether returning the value (or part of it) from the function
+/// counts as capturing it or not.
+bool llvm::PointerMayBeCaptured(const Value *V, bool ReturnCaptures) {
+ assert(isa<PointerType>(V->getType()) && "Capture is for pointers only!");
+ SmallVector<Use*, 16> Worklist;
+ SmallSet<Use*, 16> Visited;
+
+ for (Value::use_const_iterator UI = V->use_begin(), UE = V->use_end();
+ UI != UE; ++UI) {
+ Use *U = &UI.getUse();
+ Visited.insert(U);
+ Worklist.push_back(U);
+ }
+
+ while (!Worklist.empty()) {
+ Use *U = Worklist.pop_back_val();
+ Instruction *I = cast<Instruction>(U->getUser());
+ V = U->get();
+
+ switch (I->getOpcode()) {
+ case Instruction::Call:
+ case Instruction::Invoke: {
+ CallSite CS = CallSite::get(I);
+ // Not captured if the callee is readonly and doesn't return a copy
+ // through its return value.
+ if (CS.onlyReadsMemory() && I->getType() == Type::VoidTy)
+ break;
+
+ // Not captured if only passed via 'nocapture' arguments. Note that
+ // calling a function pointer does not in itself cause the pointer to
+ // be captured. This is a subtle point considering that (for example)
+ // the callee might return its own address. It is analogous to saying
+ // that loading a value from a pointer does not cause the pointer to be
+ // captured, even though the loaded value might be the pointer itself
+ // (think of self-referential objects).
+ CallSite::arg_iterator B = CS.arg_begin(), E = CS.arg_end();
+ for (CallSite::arg_iterator A = B; A != E; ++A)
+ if (A->get() == V && !CS.paramHasAttr(A - B + 1, Attribute::NoCapture))
+ // The parameter is not marked 'nocapture' - captured.
+ return true;
+ // Only passed via 'nocapture' arguments, or is the called function - not
+ // captured.
+ break;
+ }
+ case Instruction::Free:
+ // Freeing a pointer does not cause it to be captured.
+ break;
+ case Instruction::Load:
+ // Loading from a pointer does not cause it to be captured.
+ break;
+ case Instruction::Ret:
+ if (ReturnCaptures)
+ return true;
+ break;
+ case Instruction::Store:
+ if (V == I->getOperand(0))
+ // Stored the pointer - it may be captured.
+ return true;
+ // Storing to the pointee does not cause the pointer to be captured.
+ break;
+ case Instruction::BitCast:
+ case Instruction::GetElementPtr:
+ case Instruction::PHI:
+ case Instruction::Select:
+ // The original value is not captured via this if the new value isn't.
+ for (Instruction::use_iterator UI = I->use_begin(), UE = I->use_end();
+ UI != UE; ++UI) {
+ Use *U = &UI.getUse();
+ if (Visited.insert(U))
+ Worklist.push_back(U);
+ }
+ break;
+ default:
+ // Something else - be conservative and say it is captured.
+ return true;
+ }
+ }
+
+ // All uses examined - not captured.
+ return false;
+}