[llvm-commits] [llvm] r61876 - in /llvm/trunk: lib/Transforms/IPO/FunctionAttrs.cpp test/Transforms/FunctionAttrs/2009-01-02-LocalStores.ll
Duncan Sands
baldrick at free.fr
Wed Jan 7 11:39:06 PST 2009
Author: baldrick
Date: Wed Jan 7 13:39:06 2009
New Revision: 61876
URL: http://llvm.org/viewvc/llvm-project?rev=61876&view=rev
Log:
Remove alloca tracking from nocapture analysis. Not only
was it not very helpful, it was also wrong! The problem
is shown in the testcase: the alloca might be passed to
a nocapture callee which dereferences it and returns the
original pointer. But because it was a nocapture call we
think we don't need to track its uses, but we do.
Modified:
llvm/trunk/lib/Transforms/IPO/FunctionAttrs.cpp
llvm/trunk/test/Transforms/FunctionAttrs/2009-01-02-LocalStores.ll
Modified: llvm/trunk/lib/Transforms/IPO/FunctionAttrs.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/IPO/FunctionAttrs.cpp?rev=61876&r1=61875&r2=61876&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/IPO/FunctionAttrs.cpp (original)
+++ llvm/trunk/lib/Transforms/IPO/FunctionAttrs.cpp Wed Jan 7 13:39:06 2009
@@ -183,32 +183,20 @@
/// isCaptured - Return true if this pointer value may be captured.
bool FunctionAttrs::isCaptured(Function &F, Value *V) {
- typedef PointerIntPair<Use*, 2> UseWithDepth;
- SmallVector<UseWithDepth, 16> Worklist;
- SmallSet<UseWithDepth, 16> Visited;
+ SmallVector<Use*, 16> Worklist;
+ SmallSet<Use*, 16> Visited;
for (Value::use_iterator UI = V->use_begin(), UE = V->use_end(); UI != UE;
++UI) {
- UseWithDepth UD(&UI.getUse(), 0);
- Visited.insert(UD);
- Worklist.push_back(UD);
+ Use *U = &UI.getUse();
+ Visited.insert(U);
+ Worklist.push_back(U);
}
while (!Worklist.empty()) {
- UseWithDepth UD = Worklist.pop_back_val();
- Use *U = UD.getPointer();
+ Use *U = Worklist.pop_back_val();
Instruction *I = cast<Instruction>(U->getUser());
- // The value V may have any type if it comes from tracking a load.
V = U->get();
- // The depth represents the number of loads that need to be performed to
- // get back the original pointer (or a bitcast etc of it). For example,
- // if the pointer is stored to an alloca, then all uses of the alloca get
- // depth 1: if the alloca is loaded then you get the original pointer back.
- // If a load of the alloca is returned then the pointer has been captured.
- // The depth is needed in order to know which loads dereference the original
- // pointer (these do not capture), and which return a value which needs to
- // be tracked because if it is captured then so is the original pointer.
- unsigned Depth = UD.getInt();
switch (I->getOpcode()) {
case Instruction::Call:
@@ -238,66 +226,25 @@
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::Store:
- if (V == I->getOperand(0)) {
- // Stored the pointer - it may be captured. If it is stored to a local
- // object (alloca) then track that object. Otherwise give up.
- Value *Target = I->getOperand(1)->getUnderlyingObject();
- if (!isa<AllocaInst>(Target))
- // Didn't store to an obviously local object - captured.
- return true;
- if (Depth >= 3)
- // Alloca recursion too deep - give up.
- return true;
- // Analyze all uses of the alloca.
- for (Value::use_iterator UI = Target->use_begin(),
- UE = Target->use_end(); UI != UE; ++UI) {
- UseWithDepth NUD(&UI.getUse(), Depth + 1);
- if (Visited.insert(NUD))
- Worklist.push_back(NUD);
- }
- }
+ 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::Load:
case Instruction::PHI:
case Instruction::Select:
- // Track any uses of this instruction to see if they are captured.
- // First handle any special cases.
- if (isa<GetElementPtrInst>(I)) {
- // Play safe and do not accept being used as an index.
- if (V != I->getOperand(0))
- return true;
- } else if (isa<SelectInst>(I)) {
- // Play safe and do not accept being used as the condition.
- if (V == I->getOperand(0))
- return true;
- } else if (isa<LoadInst>(I)) {
- // Usually loads can be ignored because they dereference the original
- // pointer. However the loaded value needs to be tracked if loading
- // from an object that the original pointer was stored to.
- if (Depth == 0)
- // Loading the original pointer or a variation of it. This does not
- // cause the pointer to be captured. Note that the loaded value might
- // be the pointer itself (think of self-referential objects), but that
- // is fine as long as it's not this function that stored it there.
- break;
- // Loading a pointer to (a pointer to...) the original pointer or a
- // variation of it. Track uses of the loaded value, noting that one
- // dereference was performed. Note that the loaded value need not be
- // of pointer type. For example, an alloca may have been bitcast to
- // a pointer to another type, which was then loaded.
- --Depth;
- }
-
- // The original value is not captured via this if the instruction isn't.
+ // 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) {
- UseWithDepth UD(&UI.getUse(), Depth);
- if (Visited.insert(UD))
- Worklist.push_back(UD);
+ Use *U = &UI.getUse();
+ if (Visited.insert(U))
+ Worklist.push_back(U);
}
break;
default:
Modified: llvm/trunk/test/Transforms/FunctionAttrs/2009-01-02-LocalStores.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/FunctionAttrs/2009-01-02-LocalStores.ll?rev=61876&r1=61875&r2=61876&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/FunctionAttrs/2009-01-02-LocalStores.ll (original)
+++ llvm/trunk/test/Transforms/FunctionAttrs/2009-01-02-LocalStores.ll Wed Jan 7 13:39:06 2009
@@ -1,23 +1,14 @@
; RUN: llvm-as < %s | opt -functionattrs | llvm-dis | not grep {nocapture *%%q}
; RUN: llvm-as < %s | opt -functionattrs | llvm-dis | grep {nocapture *%%p}
- at g = external global i32**
-
-define i32 @f(i32* %p, i32* %q) {
- %a1 = alloca i32*
- %a2 = alloca i32**
- store i32* %p, i32** %a1
- store i32** %a1, i32*** %a2
- %reload1 = load i32*** %a2
- %reload2 = load i32** %reload1
- %load_p = load i32* %reload2
- store i32 0, i32* %reload2
+define i32* @a(i32** %p) {
+ %tmp = load i32** %p
+ ret i32* %tmp
+}
- %b1 = alloca i32*
- %b2 = alloca i32**
- store i32* %q, i32** %b1
- store i32** %b1, i32*** %b2
- %reload3 = load i32*** %b2
- store i32** %reload3, i32*** @g
- ret i32 %load_p
+define i32* @b(i32 *%q) {
+ %mem = alloca i32*
+ store i32* %q, i32** %mem
+ %tmp = call i32* @a(i32** %mem)
+ ret i32* %tmp
}
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