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Extend CaptureTracking to indicate when a value is never stored, even

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if it is not ultimately captured. Teach BasicAliasAnalysis that a 
local object address which does not escape and is never stored does
not alias with a value resulting from a load.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@89398 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Dan Gohman 2009-11-19 21:57:48 +00:00
parent 07ba906413
commit f94b5edc45
5 changed files with 143 additions and 15 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

6
include/llvm/Analysis/CaptureTracking.h
View File

@ -21,8 +21,12 @@ namespace llvm {
/// 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. The boolean StoreCaptures specified whether
/// storing the value (or part of it) into memory anywhere automatically
/// counts as capturing it or not.
bool PointerMayBeCaptured(const Value *V, bool ReturnCaptures);
bool PointerMayBeCaptured(const Value *V,
bool ReturnCaptures,
bool StoreCaptures);
} // end namespace llvm

29
lib/Analysis/BasicAliasAnalysis.cpp
View File

@ -79,7 +79,12 @@ static bool isKnownNonNull(const Value *V) {
static bool isNonEscapingLocalObject(const Value *V) {
// If this is a local allocation, check to see if it escapes.
if (isa<AllocaInst>(V) || isNoAliasCall(V))
return !PointerMayBeCaptured(V, false);
// Set StoreCaptures to True so that we can assume in our callers that the
// pointer is not the result of a load instruction. Currently
// PointerMayBeCaptured doesn't have any special analysis for the
// StoreCaptures=false case; if it did, our callers could be refined to be
// more precise.
return !PointerMayBeCaptured(V, false, /*StoreCaptures=*/true);
// 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
@ -89,7 +94,7 @@ static bool isNonEscapingLocalObject(const Value *V) {
// Don't bother analyzing arguments already known not to escape.
if (A->hasNoCaptureAttr())
return true;
return !PointerMayBeCaptured(V, false);
return !PointerMayBeCaptured(V, false, /*StoreCaptures=*/true);
}
return false;
}
@ -683,15 +688,19 @@ BasicAliasAnalysis::aliasCheck(const Value *V1, unsigned V1Size,
(V2Size != ~0U && isObjectSmallerThan(O1, V2Size, *TD)))
return NoAlias;
// If one pointer is the result of a call/invoke and the other is a
// If one pointer is the result of a call/invoke or load and the other is a
// non-escaping local object, then we know the object couldn't escape to a
// point where the call could return it.
if ((isa<CallInst>(O1) || isa<InvokeInst>(O1)) &&
isNonEscapingLocalObject(O2) && O1 != O2)
return NoAlias;
if ((isa<CallInst>(O2) || isa<InvokeInst>(O2)) &&
isNonEscapingLocalObject(O1) && O1 != O2)
return NoAlias;
// point where the call could return it. The load case works because
// isNonEscapingLocalObject considers all stores to be escapes (it
// passes true for the StoreCaptures argument to PointerMayBeCaptured).
if (O1 != O2) {
if ((isa<CallInst>(O1) || isa<InvokeInst>(O1) || isa<LoadInst>(O1)) &&
isNonEscapingLocalObject(O2))
return NoAlias;
if ((isa<CallInst>(O2) || isa<InvokeInst>(O2) || isa<LoadInst>(O2)) &&
isNonEscapingLocalObject(O1))
return NoAlias;
}
if (!isa<GEPOperator>(V1) && isa<GEPOperator>(V2)) {
std::swap(V1, V2);

11
lib/Analysis/CaptureTracking.cpp
View File

@ -28,8 +28,11 @@ using namespace llvm;
/// 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. The boolean StoreCaptures specified whether
/// storing the value (or part of it) into memory anywhere automatically
/// counts as capturing it or not.
bool llvm::PointerMayBeCaptured(const Value *V, bool ReturnCaptures) {
bool llvm::PointerMayBeCaptured(const Value *V,
bool ReturnCaptures, bool StoreCaptures) {
assert(isa<PointerType>(V->getType()) && "Capture is for pointers only!");
SmallVector<Use*, 16> Worklist;
SmallSet<Use*, 16> Visited;
@ -82,7 +85,11 @@ bool llvm::PointerMayBeCaptured(const Value *V, bool ReturnCaptures) {
break;
case Instruction::Store:
if (V == I->getOperand(0))
// Stored the pointer - it may be captured.
// Stored the pointer - conservatively assume it may be captured.
// TODO: If StoreCaptures is not true, we could do Fancy analysis
// to determine whether this store is not actually an escape point.
// In that case, BasicAliasAnalysis should be updated as well to
// take advantage of this.
return true;
// Storing to the pointee does not cause the pointer to be captured.
break;

4
lib/Transforms/IPO/FunctionAttrs.cpp
View File

@ -212,7 +212,7 @@ bool FunctionAttrs::AddNoCaptureAttrs(const std::vector<CallGraphNode *> &SCC) {
for (Function::arg_iterator A = F->arg_begin(), E = F->arg_end(); A!=E; ++A)
if (isa<PointerType>(A->getType()) && !A->hasNoCaptureAttr() &&
!PointerMayBeCaptured(A, true)) {
!PointerMayBeCaptured(A, true, /*StoreCaptures=*/false)) {
A->addAttr(Attribute::NoCapture);
++NumNoCapture;
Changed = true;
@ -280,7 +280,7 @@ bool FunctionAttrs::IsFunctionMallocLike(Function *F,
return false; // Did not come from an allocation.
}
if (PointerMayBeCaptured(RetVal, false))
if (PointerMayBeCaptured(RetVal, false, /*StoreCaptures=*/false))
return false;
}

108
test/Transforms/GVN/nonescaping-malloc.ll Normal file
View File

@ -0,0 +1,108 @@
; RUN: opt < %s -gvn -stats |& grep {Number of loads deleted}
; rdar://7363102
; GVN should be able to eliminate load %tmp22.i, because it is redundant with
; load %tmp8.i. This requires being able to prove that %tmp7.i doesn't
; alias the malloc'd value %tmp.i20.i.i, which it can do since %tmp7.i
; is derived from %tmp5.i which is computed from a load, and %tmp.i20.i.i
; is never stored and does not escape.
target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128"
target triple = "x86_64-apple-darwin10.0"
%"struct.llvm::MallocAllocator" = type <{ i8 }>
%"struct.llvm::StringMap<void*,llvm::MallocAllocator>" = type { %"struct.llvm::StringMapImpl", %"struct.llvm::MallocAllocator" }
%"struct.llvm::StringMapEntry<void*>" = type { %"struct.llvm::StringMapEntryBase", i8* }
%"struct.llvm::StringMapEntryBase" = type { i32 }
%"struct.llvm::StringMapImpl" = type { %"struct.llvm::StringMapImpl::ItemBucket"*, i32, i32, i32, i32 }
%"struct.llvm::StringMapImpl::ItemBucket" = type { i32, %"struct.llvm::StringMapEntryBase"* }
%"struct.llvm::StringRef" = type { i8*, i64 }
define %"struct.llvm::StringMapEntry<void*>"* @_Z3fooRN4llvm9StringMapIPvNS_15MallocAllocatorEEEPKc(%"struct.llvm::StringMap<void*,llvm::MallocAllocator>"* %X, i8* %P) ssp {
entry:
%tmp = alloca %"struct.llvm::StringRef", align 8 ; <%"struct.llvm::StringRef"*> [#uses=3]
%tmp.i = getelementptr inbounds %"struct.llvm::StringRef"* %tmp, i64 0, i32 0 ; <i8**> [#uses=1]
store i8* %P, i8** %tmp.i, align 8
%tmp1.i = call i64 @strlen(i8* %P) nounwind readonly ; <i64> [#uses=1]
%tmp2.i = getelementptr inbounds %"struct.llvm::StringRef"* %tmp, i64 0, i32 1 ; <i64*> [#uses=1]
store i64 %tmp1.i, i64* %tmp2.i, align 8
%tmp1 = call %"struct.llvm::StringMapEntry<void*>"* @_ZN4llvm9StringMapIPvNS_15MallocAllocatorEE16GetOrCreateValueERKNS_9StringRefE(%"struct.llvm::StringMap<void*,llvm::MallocAllocator>"* %X, %"struct.llvm::StringRef"* %tmp) ssp ; <%"struct.llvm::StringMapEntry<void*>"*> [#uses=1]
ret %"struct.llvm::StringMapEntry<void*>"* %tmp1
}
declare i64 @strlen(i8* nocapture) nounwind readonly
declare noalias i8* @malloc(i64) nounwind
declare void @llvm.memcpy.i64(i8* nocapture, i8* nocapture, i64, i32) nounwind
declare i32 @_ZN4llvm13StringMapImpl15LookupBucketForENS_9StringRefE(%"struct.llvm::StringMapImpl"*, i64, i64)
define linkonce_odr %"struct.llvm::StringMapEntry<void*>"* @_ZN4llvm9StringMapIPvNS_15MallocAllocatorEE16GetOrCreateValueERKNS_9StringRefE(%"struct.llvm::StringMap<void*,llvm::MallocAllocator>"* %this, %"struct.llvm::StringRef"* nocapture %Key) ssp align 2 {
entry:
%elt = bitcast %"struct.llvm::StringRef"* %Key to i64* ; <i64*> [#uses=1]
%val = load i64* %elt ; <i64> [#uses=3]
%tmp = getelementptr inbounds %"struct.llvm::StringRef"* %Key, i64 0, i32 1 ; <i64*> [#uses=1]
%val2 = load i64* %tmp ; <i64> [#uses=2]
%tmp2.i = getelementptr inbounds %"struct.llvm::StringMap<void*,llvm::MallocAllocator>"* %this, i64 0, i32 0 ; <%"struct.llvm::StringMapImpl"*> [#uses=1]
%tmp3.i = tail call i32 @_ZN4llvm13StringMapImpl15LookupBucketForENS_9StringRefE(%"struct.llvm::StringMapImpl"* %tmp2.i, i64 %val, i64 %val2) ; <i32> [#uses=1]
%tmp4.i = getelementptr inbounds %"struct.llvm::StringMap<void*,llvm::MallocAllocator>"* %this, i64 0, i32 0, i32 0 ; <%"struct.llvm::StringMapImpl::ItemBucket"**> [#uses=1]
%tmp5.i = load %"struct.llvm::StringMapImpl::ItemBucket"** %tmp4.i, align 8 ; <%"struct.llvm::StringMapImpl::ItemBucket"*> [#uses=1]
%tmp6.i = zext i32 %tmp3.i to i64 ; <i64> [#uses=1]
%tmp7.i = getelementptr inbounds %"struct.llvm::StringMapImpl::ItemBucket"* %tmp5.i, i64 %tmp6.i, i32 1 ; <%"struct.llvm::StringMapEntryBase"**> [#uses=2]
%tmp8.i = load %"struct.llvm::StringMapEntryBase"** %tmp7.i, align 8 ; <%"struct.llvm::StringMapEntryBase"*> [#uses=3]
%tmp9.i = icmp eq %"struct.llvm::StringMapEntryBase"* %tmp8.i, null ; <i1> [#uses=1]
%tmp13.i = icmp eq %"struct.llvm::StringMapEntryBase"* %tmp8.i, inttoptr (i64 -1 to %"struct.llvm::StringMapEntryBase"*) ; <i1> [#uses=1]
%or.cond.i = or i1 %tmp9.i, %tmp13.i ; <i1> [#uses=1]
br i1 %or.cond.i, label %bb4.i, label %bb6.i
bb4.i: ; preds = %entry
%tmp41.i = inttoptr i64 %val to i8* ; <i8*> [#uses=2]
%tmp4.i35.i = getelementptr inbounds i8* %tmp41.i, i64 %val2 ; <i8*> [#uses=1]
%tmp.i.i = ptrtoint i8* %tmp4.i35.i to i64 ; <i64> [#uses=1]
%tmp1.i.i = trunc i64 %tmp.i.i to i32 ; <i32> [#uses=1]
%tmp3.i.i = trunc i64 %val to i32 ; <i32> [#uses=1]
%tmp4.i.i = sub i32 %tmp1.i.i, %tmp3.i.i ; <i32> [#uses=3]
%tmp5.i.i = add i32 %tmp4.i.i, 17 ; <i32> [#uses=1]
%tmp8.i.i = zext i32 %tmp5.i.i to i64 ; <i64> [#uses=1]
%tmp.i20.i.i = tail call noalias i8* @malloc(i64 %tmp8.i.i) nounwind ; <i8*> [#uses=7]
%tmp10.i.i = bitcast i8* %tmp.i20.i.i to %"struct.llvm::StringMapEntry<void*>"* ; <%"struct.llvm::StringMapEntry<void*>"*> [#uses=2]
%tmp12.i.i = icmp eq i8* %tmp.i20.i.i, null ; <i1> [#uses=1]
br i1 %tmp12.i.i, label %_ZN4llvm14StringMapEntryIPvE6CreateINS_15MallocAllocatorES1_EEPS2_PKcS7_RT_T0_.exit.i, label %bb.i.i
bb.i.i: ; preds = %bb4.i
%tmp.i.i.i.i = bitcast i8* %tmp.i20.i.i to i32* ; <i32*> [#uses=1]
store i32 %tmp4.i.i, i32* %tmp.i.i.i.i, align 4
%tmp1.i19.i.i = getelementptr inbounds i8* %tmp.i20.i.i, i64 8 ; <i8*> [#uses=1]
%0 = bitcast i8* %tmp1.i19.i.i to i8** ; <i8**> [#uses=1]
store i8* null, i8** %0, align 8
br label %_ZN4llvm14StringMapEntryIPvE6CreateINS_15MallocAllocatorES1_EEPS2_PKcS7_RT_T0_.exit.i
_ZN4llvm14StringMapEntryIPvE6CreateINS_15MallocAllocatorES1_EEPS2_PKcS7_RT_T0_.exit.i: ; preds = %bb4.i, %bb.i.i
%tmp.i18.i.i = getelementptr inbounds i8* %tmp.i20.i.i, i64 16 ; <i8*> [#uses=1]
%tmp15.i.i = zext i32 %tmp4.i.i to i64 ; <i64> [#uses=2]
tail call void @llvm.memcpy.i64(i8* %tmp.i18.i.i, i8* %tmp41.i, i64 %tmp15.i.i, i32 1) nounwind
%tmp.i18.sum.i.i = add i64 %tmp15.i.i, 16 ; <i64> [#uses=1]
%tmp17.i.i = getelementptr inbounds i8* %tmp.i20.i.i, i64 %tmp.i18.sum.i.i ; <i8*> [#uses=1]
store i8 0, i8* %tmp17.i.i, align 1
%tmp.i.i.i = getelementptr inbounds i8* %tmp.i20.i.i, i64 8 ; <i8*> [#uses=1]
%1 = bitcast i8* %tmp.i.i.i to i8** ; <i8**> [#uses=1]
store i8* null, i8** %1, align 8
%tmp22.i = load %"struct.llvm::StringMapEntryBase"** %tmp7.i, align 8 ; <%"struct.llvm::StringMapEntryBase"*> [#uses=1]
%tmp24.i = icmp eq %"struct.llvm::StringMapEntryBase"* %tmp22.i, inttoptr (i64 -1 to %"struct.llvm::StringMapEntryBase"*) ; <i1> [#uses=1]
br i1 %tmp24.i, label %bb9.i, label %_ZN4llvm9StringMapIPvNS_15MallocAllocatorEE16GetOrCreateValueIS1_EERNS_14StringMapEntryIS1_EENS_9StringRefET_.exit
bb6.i: ; preds = %entry
%tmp16.i = bitcast %"struct.llvm::StringMapEntryBase"* %tmp8.i to %"struct.llvm::StringMapEntry<void*>"* ; <%"struct.llvm::StringMapEntry<void*>"*> [#uses=1]
ret %"struct.llvm::StringMapEntry<void*>"* %tmp16.i
bb9.i: ; preds = %_ZN4llvm14StringMapEntryIPvE6CreateINS_15MallocAllocatorES1_EEPS2_PKcS7_RT_T0_.exit.i
%tmp25.i = getelementptr inbounds %"struct.llvm::StringMap<void*,llvm::MallocAllocator>"* %this, i64 0, i32 0, i32 3 ; <i32*> [#uses=2]
%tmp26.i = load i32* %tmp25.i, align 8 ; <i32> [#uses=1]
%tmp27.i = add i32 %tmp26.i, -1 ; <i32> [#uses=1]
store i32 %tmp27.i, i32* %tmp25.i, align 8
ret %"struct.llvm::StringMapEntry<void*>"* %tmp10.i.i
_ZN4llvm9StringMapIPvNS_15MallocAllocatorEE16GetOrCreateValueIS1_EERNS_14StringMapEntryIS1_EENS_9StringRefET_.exit: ; preds = %_ZN4llvm14StringMapEntryIPvE6CreateINS_15MallocAllocatorES1_EEPS2_PKcS7_RT_T0_.exit.i
ret %"struct.llvm::StringMapEntry<void*>"* %tmp10.i.i
}