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, 22 insertions, 15 deletions

diff --git a/llvm/lib/Analysis/BasicAliasAnalysis.cpp b/llvm/lib/Analysis/BasicAliasAnalysis.cpp
index 883462a..9632634 100644
--- a/llvm/lib/Analysis/BasicAliasAnalysis.cpp
+++ b/llvm/lib/Analysis/BasicAliasAnalysis.cpp
@@ -85,15 +85,15 @@ const unsigned MaxNumPhiBBsValueReachabilityCheck = 20;
 // depth otherwise the algorithm in aliasGEP will assert.
 static const unsigned MaxLookupSearchDepth = 6;
 
-bool BasicAAResult::invalidate(Function &F, const PreservedAnalyses &PA,
+bool BasicAAResult::invalidate(Function &Fn, const PreservedAnalyses &PA,
                                FunctionAnalysisManager::Invalidator &Inv) {
   // We don't care if this analysis itself is preserved, it has no state. But
   // we need to check that the analyses it depends on have been. Note that we
   // may be created without handles to some analyses and in that case don't
   // depend on them.
-  if (Inv.invalidate<AssumptionAnalysis>(F, PA) ||
-      (DT && Inv.invalidate<DominatorTreeAnalysis>(F, PA)) ||
-      (LI && Inv.invalidate<LoopAnalysis>(F, PA)))
+  if (Inv.invalidate<AssumptionAnalysis>(Fn, PA) ||
+      (DT && Inv.invalidate<DominatorTreeAnalysis>(Fn, PA)) ||
+      (LI && Inv.invalidate<LoopAnalysis>(Fn, PA)))
     return true;
 
   // Otherwise this analysis result remains valid.
@@ -150,10 +150,12 @@ static bool isEscapeSource(const Value *V) {
 /// Returns the size of the object specified by V or UnknownSize if unknown.
 static uint64_t getObjectSize(const Value *V, const DataLayout &DL,
                               const TargetLibraryInfo &TLI,
+                              bool NullIsValidLoc,
                               bool RoundToAlign = false) {
   uint64_t Size;
   ObjectSizeOpts Opts;
   Opts.RoundToAlign = RoundToAlign;
+  Opts.NullIsUnknownSize = NullIsValidLoc;
   if (getObjectSize(V, Size, DL, &TLI, Opts))
     return Size;
   return MemoryLocation::UnknownSize;
@@ -163,7 +165,8 @@ static uint64_t getObjectSize(const Value *V, const DataLayout &DL,
 /// Size.
 static bool isObjectSmallerThan(const Value *V, uint64_t Size,
                                 const DataLayout &DL,
-                                const TargetLibraryInfo &TLI) {
+                                const TargetLibraryInfo &TLI,
+                                bool NullIsValidLoc) {
   // Note that the meanings of the "object" are slightly different in the
   // following contexts:
   //    c1: llvm::getObjectSize()
@@ -195,15 +198,16 @@ static bool isObjectSmallerThan(const Value *V, uint64_t Size,
 
   // This function needs to use the aligned object size because we allow
   // reads a bit past the end given sufficient alignment.
-  uint64_t ObjectSize = getObjectSize(V, DL, TLI, /*RoundToAlign*/ true);
+  uint64_t ObjectSize = getObjectSize(V, DL, TLI, NullIsValidLoc,
+                                      /*RoundToAlign*/ true);
 
   return ObjectSize != MemoryLocation::UnknownSize && ObjectSize < Size;
 }
 
 /// Returns true if we can prove that the object specified by V has size Size.
 static bool isObjectSize(const Value *V, uint64_t Size, const DataLayout &DL,
-                         const TargetLibraryInfo &TLI) {
-  uint64_t ObjectSize = getObjectSize(V, DL, TLI);
+                         const TargetLibraryInfo &TLI, bool NullIsValidLoc) {
+  uint64_t ObjectSize = getObjectSize(V, DL, TLI, NullIsValidLoc);
   return ObjectSize != MemoryLocation::UnknownSize && ObjectSize == Size;
 }
 
@@ -1623,10 +1627,10 @@ AliasResult BasicAAResult::aliasCheck(const Value *V1, LocationSize V1Size,
   // Null values in the default address space don't point to any object, so they
   // don't alias any other pointer.
   if (const ConstantPointerNull *CPN = dyn_cast<ConstantPointerNull>(O1))
-    if (CPN->getType()->getAddressSpace() == 0)
+    if (!NullPointerIsDefined(&F, CPN->getType()->getAddressSpace()))
       return NoAlias;
   if (const ConstantPointerNull *CPN = dyn_cast<ConstantPointerNull>(O2))
-    if (CPN->getType()->getAddressSpace() == 0)
+    if (!NullPointerIsDefined(&F, CPN->getType()->getAddressSpace()))
       return NoAlias;
 
   if (O1 != O2) {
@@ -1662,10 +1666,11 @@ AliasResult BasicAAResult::aliasCheck(const Value *V1, LocationSize V1Size,
 
   // If the size of one access is larger than the entire object on the other
   // side, then we know such behavior is undefined and can assume no alias.
+  bool NullIsValidLocation = NullPointerIsDefined(&F);
   if ((V1Size != MemoryLocation::UnknownSize &&
-       isObjectSmallerThan(O2, V1Size, DL, TLI)) ||
+       isObjectSmallerThan(O2, V1Size, DL, TLI, NullIsValidLocation)) ||
       (V2Size != MemoryLocation::UnknownSize &&
-       isObjectSmallerThan(O1, V2Size, DL, TLI)))
+       isObjectSmallerThan(O1, V2Size, DL, TLI, NullIsValidLocation)))
     return NoAlias;
 
   // Check the cache before climbing up use-def chains. This also terminates
@@ -1725,8 +1730,8 @@ AliasResult BasicAAResult::aliasCheck(const Value *V1, LocationSize V1Size,
   if (O1 == O2)
     if (V1Size != MemoryLocation::UnknownSize &&
         V2Size != MemoryLocation::UnknownSize &&
-        (isObjectSize(O1, V1Size, DL, TLI) ||
-         isObjectSize(O2, V2Size, DL, TLI)))
+        (isObjectSize(O1, V1Size, DL, TLI, NullIsValidLocation) ||
+         isObjectSize(O2, V2Size, DL, TLI, NullIsValidLocation)))
       return AliasCache[Locs] = PartialAlias;
 
   // Recurse back into the best AA results we have, potentially with refined
@@ -1870,6 +1875,7 @@ AnalysisKey BasicAA::Key;
 
 BasicAAResult BasicAA::run(Function &F, FunctionAnalysisManager &AM) {
   return BasicAAResult(F.getParent()->getDataLayout(),
+                       F,
                        AM.getResult<TargetLibraryAnalysis>(F),
                        AM.getResult<AssumptionAnalysis>(F),
                        &AM.getResult<DominatorTreeAnalysis>(F),
@@ -1902,7 +1908,7 @@ bool BasicAAWrapperPass::runOnFunction(Function &F) {
   auto &DTWP = getAnalysis<DominatorTreeWrapperPass>();
   auto *LIWP = getAnalysisIfAvailable<LoopInfoWrapperPass>();
 
-  Result.reset(new BasicAAResult(F.getParent()->getDataLayout(), TLIWP.getTLI(),
+  Result.reset(new BasicAAResult(F.getParent()->getDataLayout(), F, TLIWP.getTLI(),
                                  ACT.getAssumptionCache(F), &DTWP.getDomTree(),
                                  LIWP ? &LIWP->getLoopInfo() : nullptr));
 
@@ -1919,6 +1925,7 @@ void BasicAAWrapperPass::getAnalysisUsage(AnalysisUsage &AU) const {
 BasicAAResult llvm::createLegacyPMBasicAAResult(Pass &P, Function &F) {
   return BasicAAResult(
       F.getParent()->getDataLayout(),
+      F,
       P.getAnalysis<TargetLibraryInfoWrapperPass>().getTLI(),
       P.getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F));
 }