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

1 files changed, 6 insertions, 1 deletions

diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index 7ff1d52..bdfd178 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -1769,7 +1769,12 @@ bool isKnownToBeAPowerOfTwo(const Value *V, bool OrZero, unsigned Depth,
 /// Currently this routine does not support vector GEPs.
 static bool isGEPKnownNonNull(const GEPOperator *GEP, unsigned Depth,
                               const Query &Q) {
-  if (!GEP->isInBounds() || GEP->getPointerAddressSpace() != 0)
+  const Function *F = nullptr;
+  if (const Instruction *I = dyn_cast<Instruction>(GEP))
+    F = I->getFunction();
+
+  if (!GEP->isInBounds() ||
+      NullPointerIsDefined(F, GEP->getPointerAddressSpace()))
     return false;
 
   // FIXME: Support vector-GEPs.