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Constant fold: getelementptr (i8* inttoptr (i64 1 to i8*), i32 -1)

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Into: inttoptr (i64 0 to i8*)  -> null

This occurs in the example in PR1602.  With this fixed, we now compile
the example in PR1602 into fully "devirtualized" code:

define void @_Z1g1S(%struct.S* noalias  %s) {
entry:        %tmp131415 = getelementptr %struct.S* %s, i32 0, i32 0          ; <i32 (...)***> [#uses=1]        %tmp16 = load i32 (...)*** %tmp131415, align 4          ; <i32 (...)**> [#uses=1]
        %tmp26277 = load i32 (...)** %tmp16             ; <i32 (...)*> [#uses=1]
        %tmp2829 = bitcast i32 (...)* %tmp26277 to void (%struct.S*)*           ; <void (%struct.S*)*> [#uses=1]
        tail call void %tmp2829( %struct.S* %s )
        ret void
}

This still has the vtable dispatch (as required) but does not have any pointer
to method cruft left.

llvm-svn: 41046
This commit is contained in:
Chris Lattner 2007-08-13 17:09:08 +00:00
parent 54b799dc76
commit 8674db5fbf
1 changed files with 23 additions and 1 deletions
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24
lib/VMCore/ConstantFold.cpp
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@ -1427,7 +1427,7 @@ Constant *llvm::ConstantFoldGetElementPtr(const Constant *C,
// long 0, long 0)
// To: int* getelementptr ([3 x int]* %X, long 0, long 0)
//
if (CE->isCast() && NumIdx > 1 && Idx0->isNullValue())
if (CE->isCast() && NumIdx > 1 && Idx0->isNullValue()) {
if (const PointerType *SPT =
dyn_cast<PointerType>(CE->getOperand(0)->getType()))
if (const ArrayType *SAT = dyn_cast<ArrayType>(SPT->getElementType()))
@ -1436,6 +1436,28 @@ Constant *llvm::ConstantFoldGetElementPtr(const Constant *C,
if (CAT->getElementType() == SAT->getElementType())
return ConstantExpr::getGetElementPtr(
(Constant*)CE->getOperand(0), Idxs, NumIdx);
}
// Fold: getelementptr (i8* inttoptr (i64 1 to i8*), i32 -1)
// Into: inttoptr (i64 0 to i8*)
// This happens with pointers to member functions in C++.
if (CE->getOpcode() == Instruction::IntToPtr && NumIdx == 1 &&
isa<ConstantInt>(CE->getOperand(0)) && isa<ConstantInt>(Idxs[0]) &&
cast<PointerType>(CE->getType())->getElementType() == Type::Int8Ty) {
Constant *Base = CE->getOperand(0);
Constant *Offset = Idxs[0];
// Convert the smaller integer to the larger type.
if (Offset->getType()->getPrimitiveSizeInBits() <
Base->getType()->getPrimitiveSizeInBits())
Offset = ConstantExpr::getSExt(Offset, Base->getType());
else if (Base->getType()->getPrimitiveSizeInBits() <
Offset->getType()->getPrimitiveSizeInBits())
Base = ConstantExpr::getZExt(Base, Base->getType());
Base = ConstantExpr::getAdd(Base, Offset);
return ConstantExpr::getIntToPtr(Base, CE->getType());
}
}
return 0;
}