Teach MemoryBuiltins and InstructionSimplify that operator new never returns NULL.

This is safe per C++11 18.6.1.1p3: [operator new returns] a non-null pointer to
suitably aligned storage (3.7.4), or else throw a bad_alloc exception. This
requirement is binding on a replacement version of this function.

Brings us a tiny bit closer to eliminating more vector push_backs.

llvm-svn: 191310

3 files changed, 20 insertions, 6 deletions

diff --git a/llvm/lib/Analysis/InstructionSimplify.cpp b/llvm/lib/Analysis/InstructionSimplify.cpp
index af65cb74083..b867af1dc3d 100644
--- a/llvm/lib/Analysis/InstructionSimplify.cpp
+++ b/llvm/lib/Analysis/InstructionSimplify.cpp
@@ -1739,7 +1739,7 @@ static Constant *computePointerICmp(const DataLayout *TD,
   RHS = RHS->stripPointerCasts();
 
   // A non-null pointer is not equal to a null pointer.
-  if (llvm::isKnownNonNull(LHS) && isa<ConstantPointerNull>(RHS) &&
+  if (llvm::isKnownNonNull(LHS, TLI) && isa<ConstantPointerNull>(RHS) &&
       (Pred == CmpInst::ICMP_EQ || Pred == CmpInst::ICMP_NE))
     return ConstantInt::get(GetCompareTy(LHS),
                             !CmpInst::isTrueWhenEqual(Pred));
diff --git a/llvm/lib/Analysis/MemoryBuiltins.cpp b/llvm/lib/Analysis/MemoryBuiltins.cpp
index 0f0a1c98d0d..2ec2aec4aa0 100644
--- a/llvm/lib/Analysis/MemoryBuiltins.cpp
+++ b/llvm/lib/Analysis/MemoryBuiltins.cpp
@@ -35,6 +35,7 @@ enum AllocType {
   CallocLike         = 1<<1, // allocates + bzero
   ReallocLike        = 1<<2, // reallocates
   StrDupLike         = 1<<3,
+  OpNewLike          = MallocLike | (1<<4), // allocates; never returns null
   AllocLike          = MallocLike | CallocLike | StrDupLike,
   AnyAlloc           = MallocLike | CallocLike | ReallocLike | StrDupLike
 };
@@ -52,13 +53,13 @@ struct AllocFnsTy {
 static const AllocFnsTy AllocationFnData[] = {
   {LibFunc::malloc,              MallocLike,  1, 0,  -1},
   {LibFunc::valloc,              MallocLike,  1, 0,  -1},
-  {LibFunc::Znwj,                MallocLike,  1, 0,  -1}, // new(unsigned int)
+  {LibFunc::Znwj,                OpNewLike,   1, 0,  -1}, // new(unsigned int)
   {LibFunc::ZnwjRKSt9nothrow_t,  MallocLike,  2, 0,  -1}, // new(unsigned int, nothrow)
-  {LibFunc::Znwm,                MallocLike,  1, 0,  -1}, // new(unsigned long)
+  {LibFunc::Znwm,                OpNewLike,   1, 0,  -1}, // new(unsigned long)
   {LibFunc::ZnwmRKSt9nothrow_t,  MallocLike,  2, 0,  -1}, // new(unsigned long, nothrow)
-  {LibFunc::Znaj,                MallocLike,  1, 0,  -1}, // new[](unsigned int)
+  {LibFunc::Znaj,                OpNewLike,   1, 0,  -1}, // new[](unsigned int)
   {LibFunc::ZnajRKSt9nothrow_t,  MallocLike,  2, 0,  -1}, // new[](unsigned int, nothrow)
-  {LibFunc::Znam,                MallocLike,  1, 0,  -1}, // new[](unsigned long)
+  {LibFunc::Znam,                OpNewLike,   1, 0,  -1}, // new[](unsigned long)
   {LibFunc::ZnamRKSt9nothrow_t,  MallocLike,  2, 0,  -1}, // new[](unsigned long, nothrow)
   {LibFunc::posix_memalign,      MallocLike,  3, 2,  -1},
   {LibFunc::calloc,              CallocLike,  2, 0,   1},
@@ -189,6 +190,13 @@ bool llvm::isReallocLikeFn(const Value *V, const TargetLibraryInfo *TLI,
   return getAllocationData(V, ReallocLike, TLI, LookThroughBitCast);
 }
 
+/// \brief Tests if a value is a call or invoke to a library function that
+/// allocates memory and never returns null (such as operator new).
+bool llvm::isOperatorNewLikeFn(const Value *V, const TargetLibraryInfo *TLI,
+                               bool LookThroughBitCast) {
+  return getAllocationData(V, OpNewLike, TLI, LookThroughBitCast);
+}
+
 /// extractMallocCall - Returns the corresponding CallInst if the instruction
 /// is a malloc call.  Since CallInst::CreateMalloc() only creates calls, we
 /// ignore InvokeInst here.
diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index c81537543f5..e7a512ce0fd 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -15,6 +15,7 @@
 #include "llvm/Analysis/ValueTracking.h"
 #include "llvm/ADT/SmallPtrSet.h"
 #include "llvm/Analysis/InstructionSimplify.h"
+#include "llvm/Analysis/MemoryBuiltins.h"
 #include "llvm/IR/Constants.h"
 #include "llvm/IR/DataLayout.h"
 #include "llvm/IR/GlobalAlias.h"
@@ -2064,7 +2065,7 @@ bool llvm::isSafeToSpeculativelyExecute(const Value *V,
 
 /// isKnownNonNull - Return true if we know that the specified value is never
 /// null.
-bool llvm::isKnownNonNull(const Value *V) {
+bool llvm::isKnownNonNull(const Value *V, const TargetLibraryInfo *TLI) {
   // Alloca never returns null, malloc might.
   if (isa<AllocaInst>(V)) return true;
 
@@ -2075,5 +2076,10 @@ bool llvm::isKnownNonNull(const Value *V) {
   // Global values are not null unless extern weak.
   if (const GlobalValue *GV = dyn_cast<GlobalValue>(V))
     return !GV->hasExternalWeakLinkage();
+
+  // operator new never returns null.
+  if (isOperatorNewLikeFn(V, TLI, /*LookThroughBitCast=*/true))
+    return true;
+
   return false;
 }