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/Transforms/Utils/SimplifyCFG.cpp b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
index 083e83f..c87b5c1 100644
--- a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -5950,17 +5950,20 @@
// Load from null is undefined.
if (LoadInst *LI = dyn_cast<LoadInst>(Use))
if (!LI->isVolatile())
- return LI->getPointerAddressSpace() == 0;
+ return !NullPointerIsDefined(LI->getFunction(),
+ LI->getPointerAddressSpace());
// Store to null is undefined.
if (StoreInst *SI = dyn_cast<StoreInst>(Use))
if (!SI->isVolatile())
- return SI->getPointerAddressSpace() == 0 &&
+ return (!NullPointerIsDefined(SI->getFunction(),
+ SI->getPointerAddressSpace())) &&
SI->getPointerOperand() == I;
// A call to null is undefined.
if (auto CS = CallSite(Use))
- return CS.getCalledValue() == I;
+ return !NullPointerIsDefined(CS->getFunction()) &&
+ CS.getCalledValue() == I;
}
return false;
}