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Change the way the lint sanity checking pass detects misaligned memory accesses.

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Previously it was only be able to detect problems if the pointer was a numerical
value (eg inttoptr i32 1 to i32*), but not if it was an alloca or globa.  The
reason was the use of ComputeMaskedBits: imagine you have "alloca i8, align 2",
and ask ComputeMaskedBits what it knows about the bits of the alloca pointer.
It can tell you that the bottom bit is known zero (due to align 2) but it can't
tell you that bit 1 is known one.  That's because the address could be an even
multiple of 2 rather than an odd multiple, eg it might be a multiple of 4.  Thus
trying to use KnownOne is ineffective in the case of an alloca as it will never
have any bits set.  Instead look explicitly for constant offsets from allocas
and globals.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@164595 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Duncan Sands 2012-09-25 10:00:49 +00:00
parent b1cacc7423
commit 00edf4c1d8
2 changed files with 24 additions and 8 deletions
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24
lib/Analysis/Lint.cpp
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@ -412,14 +412,26 @@ void Lint::visitMemoryReference(Instruction &I,
}
if (TD) {
if (Align == 0 && Ty) Align = TD->getABITypeAlignment(Ty);
if (Align == 0 && Ty && Ty->isSized())
Align = TD->getABITypeAlignment(Ty);
if (Align != 0) {
unsigned BitWidth = TD->getTypeSizeInBits(Ptr->getType());
APInt KnownZero(BitWidth, 0), KnownOne(BitWidth, 0);
ComputeMaskedBits(Ptr, KnownZero, KnownOne, TD);
Assert1(!(KnownOne & APInt::getLowBitsSet(BitWidth, Log2_32(Align))),
"Undefined behavior: Memory reference address is misaligned", &I);
int64_t Offset = 0;
if (Value *Base = GetPointerBaseWithConstantOffset(Ptr, Offset, *TD)) {
unsigned BaseAlign = 0;
if (AllocaInst *AI = dyn_cast<AllocaInst>(Base)) {
BaseAlign = AI->getAlignment();
if (BaseAlign == 0 && AI->getAllocatedType()->isSized())
BaseAlign = TD->getABITypeAlignment(AI->getAllocatedType());
} else if (GlobalValue *GV = dyn_cast<GlobalVariable>(Base)) {
BaseAlign = GV->getAlignment();
if (BaseAlign == 0 && GV->getType()->getElementType()->isSized())
BaseAlign = TD->getABITypeAlignment(GV->getType()->getElementType());
}
Assert1((!BaseAlign || Align <= MinAlign(BaseAlign, Offset)),
"Undefined behavior: Memory reference address is misaligned",
&I);
}
}
}
}

8
test/Other/lint.ll
View File

@ -11,6 +11,8 @@ declare void @one_arg(i32)
@CG = constant i32 7
define i32 @foo() noreturn {
%buf = alloca i8
%buf2 = alloca {i8, i8}, align 2
; CHECK: Caller and callee calling convention differ
call void @bar()
; CHECK: Null pointer dereference
@ -26,8 +28,10 @@ define i32 @foo() noreturn {
; CHECK: Address one pointer dereference
store i32 0, i32* inttoptr (i64 1 to i32*)
; CHECK: Memory reference address is misaligned
%x = inttoptr i32 1 to i32*
load i32* %x, align 4
store i8 0, i8* %buf, align 2
; CHECK: Memory reference address is misaligned
%gep = getelementptr {i8, i8}* %buf2, i32 0, i32 1
store i8 0, i8* %gep, align 2
; CHECK: Division by zero
%sd = sdiv i32 2, 0
; CHECK: Division by zero