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Move the capture analysis from MemoryDependencyAnalysis to a more general place

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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


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@156776 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chad Rosier
2012-05-14 20:35:04 +00:00
parent 5262abb268
commit 3a884f5c17
6 changed files with 128 additions and 89 deletions
Download Patch File Download Diff File Expand all files Collapse all files
lib/Analysis/MemoryDependenceAnalysis.cpp
+5 -85
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@@ -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;