Move the capture analysis from MemoryDependencyAnalysis to a more general place

so that it can be reused in MemCpyOptimizer.  This analysis is needed to remove
an unnecessary memcpy when returning a struct into a local variable.
rdar://11341081
PR12686

llvm-svn: 156776

include/llvm/Analysis/AliasAnalysis.h

@@ -50,6 +50,7 @@ class Pass;
 class AnalysisUsage;
 class MemTransferInst;
 class MemIntrinsic;
+class DominatorTree;
 
 class AliasAnalysis {
 protected:
@@ -462,6 +463,18 @@ public:
   virtual ModRefResult getModRefInfo(ImmutableCallSite CS1,
                                      ImmutableCallSite CS2);
 
+  /// callCapturesBefore - Return information about whether a particular call 
+  /// site modifies or reads the specified memory location.
+  ModRefResult callCapturesBefore(const Instruction *I,
+                                  const AliasAnalysis::Location &MemLoc,
+                                  DominatorTree *DT);
+
+  /// callCapturesBefore - A convenience wrapper.
+  ModRefResult callCapturesBefore(const Instruction *I, const Value *P,
+                                  uint64_t Size, DominatorTree *DT) {
+    return callCapturesBefore(I, Location(P, Size), DT);
+  }
+
   //===--------------------------------------------------------------------===//
   /// Higher level methods for querying mod/ref information.
   ///

include/llvm/Analysis/MemoryDependenceAnalysis.h

@@ -431,9 +431,6 @@ namespace llvm {
 
     void RemoveCachedNonLocalPointerDependencies(ValueIsLoadPair P);
     
-    AliasAnalysis::ModRefResult
-    getModRefInfo(const Instruction *Inst, const AliasAnalysis::Location &Loc);
-
     /// verifyRemoved - Verify that the specified instruction does not occur
     /// in our internal data structures.
     void verifyRemoved(Instruction *Inst) const;

lib/Analysis/AliasAnalysis.cpp

@@ -25,6 +25,9 @@
 //===----------------------------------------------------------------------===//
 
 #include "llvm/Analysis/AliasAnalysis.h"
+#include "llvm/Analysis/CaptureTracking.h"
+#include "llvm/Analysis/Dominators.h"
+#include "llvm/Analysis/ValueTracking.h"
 #include "llvm/Pass.h"
 #include "llvm/BasicBlock.h"
 #include "llvm/Function.h"
@@ -356,6 +359,86 @@ AliasAnalysis::getModRefInfo(const AtomicRMWInst *RMW, const Location &Loc) {
   return ModRef;
 }
 
+namespace {
+  /// Only find pointer captures which happen before the given instruction. Uses
+  /// the dominator tree to determine whether one instruction is before another.
+  struct CapturesBefore : public CaptureTracker {
+    CapturesBefore(const Instruction *I, DominatorTree *DT)
+      : BeforeHere(I), DT(DT), Captured(false) {}
+
+    void tooManyUses() { Captured = true; }
+
+    bool shouldExplore(Use *U) {
+      Instruction *I = cast<Instruction>(U->getUser());
+      BasicBlock *BB = I->getParent();
+      if (BeforeHere != I &&
+          (!DT->isReachableFromEntry(BB) || DT->dominates(BeforeHere, I)))
+        return false;
+      return true;
+    }
+
+    bool captured(Use *U) {
+      Instruction *I = cast<Instruction>(U->getUser());
+      BasicBlock *BB = I->getParent();
+      if (BeforeHere != I &&
+          (!DT->isReachableFromEntry(BB) || DT->dominates(BeforeHere, I)))
+        return false;
+      Captured = true;
+      return true;
+    }
+
+    const Instruction *BeforeHere;
+    DominatorTree *DT;
+
+    bool Captured;
+  };
+}
+
+// FIXME: this is really just shoring-up a deficiency in alias analysis.
+// BasicAA isn't willing to spend linear time determining whether an alloca
+// was captured before or after this particular call, while we are. However,
+// with a smarter AA in place, this test is just wasting compile time.
+AliasAnalysis::ModRefResult
+AliasAnalysis::callCapturesBefore(const Instruction *I,
+                                  const AliasAnalysis::Location &MemLoc,
+                                  DominatorTree *DT) {
+  if (!DT || !TD) return AliasAnalysis::ModRef;
+
+  const Value *Object = GetUnderlyingObject(MemLoc.Ptr, TD);
+  if (!isIdentifiedObject(Object) || isa<GlobalValue>(Object) ||
+      isa<Constant>(Object))
+    return AliasAnalysis::ModRef;
+
+  ImmutableCallSite CS(I);
+  if (!CS.getInstruction() || CS.getInstruction() == Object)
+    return AliasAnalysis::ModRef;
+
+  CapturesBefore CB(I, DT);
+  llvm::PointerMayBeCaptured(Object, &CB);
+  if (CB.Captured)
+    return AliasAnalysis::ModRef;
+
+  unsigned ArgNo = 0;
+  for (ImmutableCallSite::arg_iterator CI = CS.arg_begin(), CE = CS.arg_end();
+       CI != CE; ++CI, ++ArgNo) {
+    // Only look at the no-capture or byval pointer arguments.  If this
+    // pointer were passed to arguments that were neither of these, then it
+    // couldn't be no-capture.
+    if (!(*CI)->getType()->isPointerTy() ||
+        (!CS.doesNotCapture(ArgNo) && !CS.isByValArgument(ArgNo)))
+      continue;
+
+    // If this is a no-capture pointer argument, see if we can tell that it
+    // is impossible to alias the pointer we're checking.  If not, we have to
+    // assume that the call could touch the pointer, even though it doesn't
+    // escape.
+    if (!isNoAlias(AliasAnalysis::Location(*CI),
+                   AliasAnalysis::Location(Object))) {
+      return AliasAnalysis::ModRef;
+    }
+  }
+  return AliasAnalysis::NoModRef;
+}
 
 // AliasAnalysis destructor: DO NOT move this to the header file for
 // AliasAnalysis or else clients of the AliasAnalysis class may not depend on

lib/Analysis/MemoryDependenceAnalysis.cpp

@@ -16,13 +16,11 @@
 
 #define DEBUG_TYPE "memdep"
 #include "llvm/Analysis/MemoryDependenceAnalysis.h"
-#include "llvm/Analysis/ValueTracking.h"
 #include "llvm/Instructions.h"
 #include "llvm/IntrinsicInst.h"
 #include "llvm/Function.h"
 #include "llvm/LLVMContext.h"
 #include "llvm/Analysis/AliasAnalysis.h"
-#include "llvm/Analysis/CaptureTracking.h"
 #include "llvm/Analysis/Dominators.h"
 #include "llvm/Analysis/InstructionSimplify.h"
 #include "llvm/Analysis/MemoryBuiltins.h"
@@ -339,88 +337,6 @@ getLoadLoadClobberFullWidthSize(const Value *MemLocBase, int64_t MemLocOffs,
   }
 }
 
-namespace {
-  /// Only find pointer captures which happen before the given instruction. Uses
-  /// the dominator tree to determine whether one instruction is before another.
-  struct CapturesBefore : public CaptureTracker {
-    CapturesBefore(const Instruction *I, DominatorTree *DT)
-      : BeforeHere(I), DT(DT), Captured(false) {}
-
-    void tooManyUses() { Captured = true; }
-
-    bool shouldExplore(Use *U) {
-      Instruction *I = cast<Instruction>(U->getUser());
-      BasicBlock *BB = I->getParent();
-      if (BeforeHere != I &&
-          (!DT->isReachableFromEntry(BB) || DT->dominates(BeforeHere, I)))
-        return false;
-      return true;
-    }
-
-    bool captured(Use *U) {
-      Instruction *I = cast<Instruction>(U->getUser());
-      BasicBlock *BB = I->getParent();
-      if (BeforeHere != I &&
-          (!DT->isReachableFromEntry(BB) || DT->dominates(BeforeHere, I)))
-        return false;
-      Captured = true;
-      return true;
-    }
-
-    const Instruction *BeforeHere;
-    DominatorTree *DT;
-
-    bool Captured;
-  };
-}
-
-AliasAnalysis::ModRefResult
-MemoryDependenceAnalysis::getModRefInfo(const Instruction *Inst,
-                                        const AliasAnalysis::Location &MemLoc) {
-  AliasAnalysis::ModRefResult MR = AA->getModRefInfo(Inst, MemLoc);
-  if (MR != AliasAnalysis::ModRef) return MR;
-
-  // FIXME: this is really just shoring-up a deficiency in alias analysis.
-  // BasicAA isn't willing to spend linear time determining whether an alloca
-  // was captured before or after this particular call, while we are. However,
-  // with a smarter AA in place, this test is just wasting compile time.
-  if (!DT) return AliasAnalysis::ModRef;
-  const Value *Object = GetUnderlyingObject(MemLoc.Ptr, TD);
-  if (!isIdentifiedObject(Object) || isa<GlobalValue>(Object) ||
-      isa<Constant>(Object))
-    return AliasAnalysis::ModRef;
-
-  ImmutableCallSite CS(Inst);
-  if (!CS.getInstruction() || CS.getInstruction() == Object)
-    return AliasAnalysis::ModRef;
-
-  CapturesBefore CB(Inst, DT);
-  llvm::PointerMayBeCaptured(Object, &CB);
-  if (CB.Captured)
-    return AliasAnalysis::ModRef;
-
-  unsigned ArgNo = 0;
-  for (ImmutableCallSite::arg_iterator CI = CS.arg_begin(), CE = CS.arg_end();
-       CI != CE; ++CI, ++ArgNo) {
-    // Only look at the no-capture or byval pointer arguments.  If this
-    // pointer were passed to arguments that were neither of these, then it
-    // couldn't be no-capture.
-    if (!(*CI)->getType()->isPointerTy() ||
-        (!CS.doesNotCapture(ArgNo) && !CS.isByValArgument(ArgNo)))
-      continue;
-
-    // If this is a no-capture pointer argument, see if we can tell that it
-    // is impossible to alias the pointer we're checking.  If not, we have to
-    // assume that the call could touch the pointer, even though it doesn't
-    // escape.
-    if (!AA->isNoAlias(AliasAnalysis::Location(*CI),
-                       AliasAnalysis::Location(Object))) {
-      return AliasAnalysis::ModRef;
-    }
-  }
-  return AliasAnalysis::NoModRef;
-}
-
 /// getPointerDependencyFrom - Return the instruction on which a memory
 /// location depends.  If isLoad is true, this routine ignores may-aliases with
 /// read-only operations.  If isLoad is false, this routine ignores may-aliases
@@ -568,7 +484,11 @@ getPointerDependencyFrom(const AliasAnalysis::Location &MemLoc, bool isLoad,
     }
 
     // See if this instruction (e.g. a call or vaarg) mod/ref's the pointer.
-    switch (getModRefInfo(Inst, MemLoc)) {
+    AliasAnalysis::ModRefResult MR = AA->getModRefInfo(Inst, MemLoc);
+    // If necessary, perform additional analysis.
+    if (MR == AliasAnalysis::ModRef)
+      MR = AA->callCapturesBefore(Inst, MemLoc, DT);
+    switch (MR) {
     case AliasAnalysis::NoModRef:
       // If the call has no effect on the queried pointer, just ignore it.
       continue;

lib/Transforms/Scalar/MemCpyOptimizer.cpp

@@ -662,7 +662,11 @@ bool MemCpyOpt::performCallSlotOptzn(Instruction *cpy,
   // the use analysis, we also need to know that it does not sneakily
   // access dest.  We rely on AA to figure this out for us.
   AliasAnalysis &AA = getAnalysis<AliasAnalysis>();
-  if (AA.getModRefInfo(C, cpyDest, srcSize) != AliasAnalysis::NoModRef)
+  AliasAnalysis::ModRefResult MR = AA.getModRefInfo(C, cpyDest, srcSize);
+  // If necessary, perform additional analysis.
+  if (MR != AliasAnalysis::NoModRef)
+    MR = AA.callCapturesBefore(C, cpyDest, srcSize, &DT);
+  if (MR != AliasAnalysis::NoModRef)
     return false;
 
   // All the checks have passed, so do the transformation.

test/Transforms/MemCpyOpt/memcpy.ll

@@ -148,3 +148,25 @@ define void @test8() {
 }
 
 declare noalias i8* @malloc(i32)
+
+; rdar://11341081
+%struct.big = type { [50 x i32] }
+
+define void @test9() nounwind uwtable ssp {
+entry:
+; CHECK: test9
+; CHECK: f1
+; CHECK-NOT: memcpy
+; CHECK: f2
+  %b = alloca %struct.big, align 4
+  %tmp = alloca %struct.big, align 4
+  call void @f1(%struct.big* sret %tmp)
+  %0 = bitcast %struct.big* %b to i8*
+  %1 = bitcast %struct.big* %tmp to i8*
+  call void @llvm.memcpy.p0i8.p0i8.i64(i8* %0, i8* %1, i64 200, i32 4, i1 false)
+  call void @f2(%struct.big* %b)
+  ret void
+}
+
+declare void @f1(%struct.big* sret)
+declare void @f2(%struct.big*)