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Rework constant expr and array handling for objectsize instcombining.

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Fix bugs where we would compute out of bounds as in bounds, and where
we couldn't know that the linker could override the size of an array.

Add a few new testcases, change existing testcase to use a private
global array instead of extern.

llvm-svn: 95283
This commit is contained in:
Eric Christopher 2010-02-04 02:55:34 +00:00
parent 3c93245a64
commit 9b3e42f09e
2 changed files with 60 additions and 24 deletions
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70
lib/Transforms/InstCombine/InstCombineCalls.cpp
View File

@ -635,43 +635,69 @@ Instruction *InstCombiner::visitCallInst(CallInst &CI) {
case Intrinsic::objectsize: {
const Type *ReturnTy = CI.getType();
Value *Op1 = II->getOperand(1);
// If we've got a GEP we're going to do some calculations
size_t GEPindex = 0;
// If we're a constant expr then we just return the number of bytes
// left in whatever we're indexing. Since it's constant there's no
// need for maximum or minimum bytes.
// Strip any casts we see and continue processing.
Op1 = Op1->stripPointerCasts();
// Make sure we can reliably know the size.
if (GlobalVariable *GV = dyn_cast<GlobalVariable>(Op1))
if (!GV->hasDefinitiveInitializer()) break;
if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Op1)) {
// If this isn't a GEP give up.
if (CE->getOpcode() != Instruction::GetElementPtr) return 0;
// If this isn't a GEP give up.
if (CE->getOpcode() != Instruction::GetElementPtr) break;
const PointerType *ObjTy =
reinterpret_cast<const PointerType*>(CE->getOperand(0)->getType());
// If this isn't guaranteed to be inbounds, give up.
bool OOB = false;
GEPOperator *GEPO = cast<GEPOperator>(Op1);
if (!GEPO->isInBounds()) OOB = true;
for (int i = GEPO->getNumIndices() - 1; i > 0; i--) {
if (Constant *C = dyn_cast<Constant>(GEPO->getOperand(i)))
if (C->isNullValue())
continue;
OOB = true;
}
// If we're guaranteed to be out of bounds just return that there's
// no room left.
if (OOB) return ReplaceInstUsesWith(CI, ConstantInt::get(ReturnTy, 0));
if (const ArrayType *AT = dyn_cast<ArrayType>(ObjTy->getElementType())) {
// Tell the later calculation that we have an offset and what
// it is.
Op1 = CE->getOperand(0);
ConstantInt *Const =
cast<ConstantInt>(CE->getOperand(CE->getNumOperands() - 1));
GEPindex = Const->getZExtValue();
}
// This may be a pointer to an array. If we have an index from earlier
// use that too.
if (const PointerType *PT = dyn_cast<PointerType>(Op1->getType())) {
if (const ArrayType *AT = dyn_cast<ArrayType>(PT->getElementType())) {
// Deal with multi-dimensional arrays
const ArrayType *SAT = AT;
while ((AT = dyn_cast<ArrayType>(AT->getElementType())))
SAT = AT;
size_t numElems = SAT->getNumElements();
// If numElems is 0, we don't know how large the array is so we can't
// make any determinations yet.
if (numElems == 0) break;
// We return the remaining bytes, so grab the size of an element
// in bytes.
size_t sizeofElem = SAT->getElementType()->getPrimitiveSizeInBits() / 8;
// in bytes and the number of elements.
if (!SAT->isSized() || !TD) break;
ConstantInt *Const =
cast<ConstantInt>(CE->getOperand(CE->getNumOperands() - 1));
size_t indx = Const->getZExtValue();
return ReplaceInstUsesWith(CI,
ConstantInt::get(ReturnTy,
((numElems - indx) * sizeofElem)));
size_t sizeofElem = TD->getTypeAllocSize(SAT->getElementType());
size_t numElems = SAT->getNumElements();
size_t remSize = (numElems - GEPindex) * sizeofElem;
return ReplaceInstUsesWith(CI, ConstantInt::get(ReturnTy, remSize));
}
}
// TODO: Add more types here.
// TODO: Check for type isSized() here as well.
}
}

14
test/Transforms/InstCombine/objsize.ll
View File

@ -1,5 +1,9 @@
; Test a pile of objectsize bounds checking.
; RUN: opt < %s -instcombine -S | FileCheck %s
@a = common global [60 x i8] zeroinitializer, align 1 ; <[60 x i8]*>
; We need target data to get the sizes of the arrays and structures.
target datalayout = "e-p:32:32:32-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:32:64-f32:32:32-f64:32:64-v64:64:64-v128:128:128-a0:0:64-f80:128:128"
@a = private global [60 x i8] zeroinitializer, align 1 ; <[60 x i8]*>
@.str = private constant [8 x i8] c"abcdefg\00" ; <[8 x i8]*>
define i32 @foo() nounwind {
@ -27,6 +31,13 @@ cond.false:
ret i8* %2;
}
define i32 @f() nounwind {
; CHECK: @f
; CHECK-NEXT: ret i32 0
%1 = call i32 @llvm.objectsize.i32(i8* getelementptr ([60 x i8]* @a, i32 1, i32 0), i1 false)
ret i32 %1
}
@window = external global [0 x i8]
define i1 @baz() nounwind {
@ -37,5 +48,4 @@ define i1 @baz() nounwind {
ret i1 %2
}
declare i32 @llvm.objectsize.i32(i8*, i1) nounwind readonly