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/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;
+}