llvm: Add support for "-fno-delete-null-pointer-checks"
Summary:
Support for this option is needed for building Linux kernel.
This is a very frequently requested feature by kernel developers.
More details : https://lkml.org/lkml/2018/4/4/601
GCC option description for -fdelete-null-pointer-checks:
This Assume that programs cannot safely dereference null pointers,
and that no code or data element resides at address zero.
-fno-delete-null-pointer-checks is the inverse of this implying that
null pointer dereferencing is not undefined.
This feature is implemented in LLVM IR in this CL as the function attribute
"null-pointer-is-valid"="true" in IR (Under review at D47894).
The CL updates several passes that assumed null pointer dereferencing is
undefined to not optimize when the "null-pointer-is-valid"="true"
attribute is present.
Reviewers: t.p.northover, efriedma, jyknight, chandlerc, rnk, srhines, void, george.burgess.iv
Reviewed By: efriedma, george.burgess.iv
Subscribers: eraman, haicheng, george.burgess.iv, drinkcat, theraven, reames, sanjoy, xbolva00, llvm-commits
Differential Revision: https://reviews.llvm.org/D47895
llvm-svn: 336613
diff --git a/llvm/lib/Analysis/LazyValueInfo.cpp b/llvm/lib/Analysis/LazyValueInfo.cpp
index a133357..435b6f2 100644
--- a/llvm/lib/Analysis/LazyValueInfo.cpp
+++ b/llvm/lib/Analysis/LazyValueInfo.cpp
@@ -704,9 +704,11 @@
assert(isa<Argument>(Val) && "Unknown live-in to the entry block");
// Before giving up, see if we can prove the pointer non-null local to
// this particular block.
- if (Val->getType()->isPointerTy() &&
- (isKnownNonZero(Val, DL) || isObjectDereferencedInBlock(Val, BB))) {
- PointerType *PTy = cast<PointerType>(Val->getType());
+ PointerType *PTy = dyn_cast<PointerType>(Val->getType());
+ if (PTy &&
+ (isKnownNonZero(Val, DL) ||
+ (isObjectDereferencedInBlock(Val, BB) &&
+ !NullPointerIsDefined(BB->getParent(), PTy->getAddressSpace())))) {
Result = ValueLatticeElement::getNot(ConstantPointerNull::get(PTy));
} else {
Result = ValueLatticeElement::getOverdefined();
@@ -739,9 +741,9 @@
<< "' - overdefined because of pred (non local).\n");
// Before giving up, see if we can prove the pointer non-null local to
// this particular block.
- if (Val->getType()->isPointerTy() &&
- isObjectDereferencedInBlock(Val, BB)) {
- PointerType *PTy = cast<PointerType>(Val->getType());
+ PointerType *PTy = dyn_cast<PointerType>(Val->getType());
+ if (PTy && isObjectDereferencedInBlock(Val, BB) &&
+ !NullPointerIsDefined(BB->getParent(), PTy->getAddressSpace())) {
Result = ValueLatticeElement::getNot(ConstantPointerNull::get(PTy));
}