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

include/llvm/Analysis/MemoryBuiltins.h

@@ -64,6 +64,10 @@ bool isAllocLikeFn(const Value *V, const TargetLibraryInfo *TLI,
 bool isReallocLikeFn(const Value *V, const TargetLibraryInfo *TLI,
                      bool LookThroughBitCast = false);
 
+/// \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 isOperatorNewLikeFn(const Value *V, const TargetLibraryInfo *TLI,
+                         bool LookThroughBitCast = false);
 
 //===----------------------------------------------------------------------===//
 //  malloc Call Utility Functions.

include/llvm/Analysis/ValueTracking.h

@@ -25,6 +25,7 @@ namespace llvm {
   class DataLayout;
   class StringRef;
   class MDNode;
+  class TargetLibraryInfo;
 
   /// ComputeMaskedBits - Determine which of the bits specified in Mask are
   /// known to be either zero or one and return them in the KnownZero/KnownOne
@@ -186,7 +187,7 @@ namespace llvm {
   /// isKnownNonNull - Return true if this pointer couldn't possibly be null by
   /// its definition.  This returns true for allocas, non-extern-weak globals
   /// and byval arguments.
-  bool isKnownNonNull(const Value *V);
+  bool isKnownNonNull(const Value *V, const TargetLibraryInfo *TLI = 0);
 
 } // end namespace 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));

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.

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;
 }

test/Transforms/InstSimplify/call.ll

@@ -101,3 +101,23 @@ define float @test_idempotence(float %a) {
 
   ret float %r4
 }
+
+define i8* @operator_new() {
+entry:
+  %call = tail call noalias i8* @_Znwm(i64 8)
+  %cmp = icmp eq i8* %call, null
+  br i1 %cmp, label %cast.end, label %cast.notnull
+
+cast.notnull:                                     ; preds = %entry
+  %add.ptr = getelementptr inbounds i8* %call, i64 4
+  br label %cast.end
+
+cast.end:                                         ; preds = %cast.notnull, %entry
+  %cast.result = phi i8* [ %add.ptr, %cast.notnull ], [ null, %entry ]
+  ret i8* %cast.result
+
+; CHECK-LABEL: @operator_new
+; CHECK: br i1 false, label %cast.end, label %cast.notnull
+}
+
+declare noalias i8* @_Znwm(i64)