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Add support for invariant.start inside the static constructor evaluator. This is 

useful to represent a variable that is const in the source but can't be constant
in the IR because of a non-trivial constructor. If globalopt evaluates the
constructor, and there was an invariant.start with no matching invariant.end
possible, it will mark the global constant afterwards.

llvm-svn: 150794
This commit is contained in:
Nick Lewycky 2012-02-17 06:59:21 +00:00
parent e070fd2ac8
commit 68f9f9d9c8
2 changed files with 81 additions and 12 deletions
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59
llvm/lib/Transforms/IPO/GlobalOpt.cpp
View File

@ -2295,6 +2295,7 @@ static bool EvaluateFunction(Function *F, Constant *&RetVal,
DenseMap<Constant*, Constant*> &MutatedMemory,
std::vector<GlobalVariable*> &AllocaTmps,
SmallPtrSet<Constant*, 8> &SimpleConstants,
SmallPtrSet<GlobalVariable*, 8> &Invariants,
const TargetData *TD,
const TargetLibraryInfo *TLI);
@ -2307,6 +2308,7 @@ static bool EvaluateBlock(BasicBlock::iterator CurInst, BasicBlock *&NextBB,
DenseMap<Constant*, Constant*> &MutatedMemory,
std::vector<GlobalVariable*> &AllocaTmps,
SmallPtrSet<Constant*, 8> &SimpleConstants,
SmallPtrSet<GlobalVariable*, 8> &Invariants,
const TargetData *TD,
const TargetLibraryInfo *TLI) {
// This is the main evaluation loop.
@ -2415,14 +2417,39 @@ static bool EvaluateBlock(BasicBlock::iterator CurInst, BasicBlock *&NextBB,
// Cannot handle inline asm.
if (isa<InlineAsm>(CS.getCalledValue())) return false;
if (MemSetInst *MSI = dyn_cast<MemSetInst>(CS.getInstruction())) {
if (MSI->isVolatile()) return false;
Constant *Ptr = getVal(Values, MSI->getDest());
Constant *Val = getVal(Values, MSI->getValue());
Constant *DestVal = ComputeLoadResult(getVal(Values, Ptr),
MutatedMemory);
if (Val->isNullValue() && DestVal && DestVal->isNullValue()) {
// This memset is a no-op.
if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(CS.getInstruction())) {
if (MemSetInst *MSI = dyn_cast<MemSetInst>(II)) {
if (MSI->isVolatile()) return false;
Constant *Ptr = getVal(Values, MSI->getDest());
Constant *Val = getVal(Values, MSI->getValue());
Constant *DestVal = ComputeLoadResult(getVal(Values, Ptr),
MutatedMemory);
if (Val->isNullValue() && DestVal && DestVal->isNullValue()) {
// This memset is a no-op.
++CurInst;
continue;
}
}
if (II->getIntrinsicID() == Intrinsic::lifetime_start ||
II->getIntrinsicID() == Intrinsic::lifetime_end) {
++CurInst;
continue;
}
if (II->getIntrinsicID() == Intrinsic::invariant_start) {
// We don't insert an entry into Values, as it doesn't have a
// meaningful return value.
if (!II->use_empty())
return false;
ConstantInt *Size = cast<ConstantInt>(II->getArgOperand(0));
if (Size->isAllOnesValue()) {
Value *PtrArg = getVal(Values, II->getArgOperand(1));
Value *Ptr = PtrArg->stripPointerCasts();
if (GlobalVariable *GV = dyn_cast<GlobalVariable>(Ptr))
Invariants.insert(GV);
}
// Continue even if we do nothing.
++CurInst;
continue;
}
@ -2453,8 +2480,8 @@ static bool EvaluateBlock(BasicBlock::iterator CurInst, BasicBlock *&NextBB,
Constant *RetVal;
// Execute the call, if successful, use the return value.
if (!EvaluateFunction(Callee, RetVal, Formals, CallStack,
MutatedMemory, AllocaTmps, SimpleConstants, TD,
TLI))
MutatedMemory, AllocaTmps, SimpleConstants,
Invariants, TD, TLI))
return false;
InstResult = RetVal;
@ -2521,6 +2548,7 @@ static bool EvaluateFunction(Function *F, Constant *&RetVal,
DenseMap<Constant*, Constant*> &MutatedMemory,
std::vector<GlobalVariable*> &AllocaTmps,
SmallPtrSet<Constant*, 8> &SimpleConstants,
SmallPtrSet<GlobalVariable*, 8> &Invariants,
const TargetData *TD,
const TargetLibraryInfo *TLI) {
// Check to see if this function is already executing (recursion). If so,
@ -2552,7 +2580,7 @@ static bool EvaluateFunction(Function *F, Constant *&RetVal,
while (1) {
BasicBlock *NextBB;
if (!EvaluateBlock(CurInst, NextBB, CallStack, Values, MutatedMemory,
AllocaTmps, SimpleConstants, TD, TLI))
AllocaTmps, SimpleConstants, Invariants, TD, TLI))
return false;
if (NextBB == 0) {
@ -2607,12 +2635,16 @@ static bool EvaluateStaticConstructor(Function *F, const TargetData *TD,
// simple enough to live in a static initializer of a global.
SmallPtrSet<Constant*, 8> SimpleConstants;
// Invariants - These global variables have been marked invariant by the
// static constructor.
SmallPtrSet<GlobalVariable*, 8> Invariants;
// Call the function.
Constant *RetValDummy;
bool EvalSuccess = EvaluateFunction(F, RetValDummy,
SmallVector<Constant*, 0>(), CallStack,
MutatedMemory, AllocaTmps,
SimpleConstants, TD, TLI);
SimpleConstants, Invariants, TD, TLI);
if (EvalSuccess) {
// We succeeded at evaluation: commit the result.
@ -2622,6 +2654,9 @@ static bool EvaluateStaticConstructor(Function *F, const TargetData *TD,
for (DenseMap<Constant*, Constant*>::iterator I = MutatedMemory.begin(),
E = MutatedMemory.end(); I != E; ++I)
CommitValueTo(I->second, I->first);
for (SmallPtrSet<GlobalVariable*, 8>::iterator I = Invariants.begin(),
E = Invariants.end(); I != E; ++I)
(*I)->setConstant(true);
}
// At this point, we are done interpreting. If we created any 'alloca'

34
llvm/test/Transforms/GlobalOpt/invariant.ll Normal file
View File

@ -0,0 +1,34 @@
; RUN: opt -globalopt -S -o - < %s | FileCheck %s
declare {}* @llvm.invariant.start(i64 %size, i8* nocapture %ptr)
define void @test1(i8* %ptr) {
call {}* @llvm.invariant.start(i64 -1, i8* %ptr)
ret void
}
@object1 = global i32 0
; CHECK: @object1 = constant i32 -1
define void @ctor1() {
store i32 -1, i32* @object1
%A = bitcast i32* @object1 to i8*
call void @test1(i8* %A)
ret void
}
@object2 = global i32 0
; CHECK: @object2 = global i32 0
define void @ctor2() {
store i32 -1, i32* @object2
%A = bitcast i32* @object2 to i8*
%B = call {}* @llvm.invariant.start(i64 -1, i8* %A)
; Why in the world does this pass the verifier?
%C = bitcast {}* %B to i8*
ret void
}
@llvm.global_ctors = appending constant
[2 x { i32, void ()* }]
[ { i32, void ()* } { i32 65535, void ()* @ctor1 },
{ i32, void ()* } { i32 65535, void ()* @ctor2 } ]