[ValueTracking] Dereferenceable and !NullPointerIsDefined imply non-zero

[nikic]

This needs a rebase.

[StephenFan]

Rebase.

[goldstein.w.n]

llvm/test/Transforms/InstSimplify/icmp.ll

279

These tests should be precommited.

[nikic]

llvm/lib/Analysis/ValueTracking.cpp

2686–2694

Move this behind the PointerType check as well.

[StephenFan]

Refact.

[StephenFan]

llvm/test/Transforms/InstSimplify/icmp.ll

279

Thanks for pointing it out. I will precommit it before landing.

[nikic]

LGTM

llvm/lib/Analysis/ValueTracking.cpp

if (const auto *EEI = dyn_cast<ExtractElementInst>(I)) {
         return isKnownNonZero(Vec, DemandedVecElts, Depth, Q);
       }
     }
     break;
   case Instruction::Freeze:
     return isKnownNonZero(I->getOperand(0), Depth, Q) &&
            isGuaranteedNotToBePoison(I->getOperand(0), Q.AC, Q.CxtI, Q.DT,
                                      Depth);
-  case Instruction::Load:
-    // A Load tagged with nonnull metadata is never null.
-    if (Q.IIQ.getMetadata(cast<LoadInst>(I), LLVMContext::MD_nonnull))
+  case Instruction::Load: {
+    auto *LI = cast<LoadInst>(I);
+    // A Load tagged with nonnull or dereferenceable with null pointer undefined
+    // is never null.
+    if (auto *PtrT = dyn_cast<PointerType>(I->getType()))
+      if (Q.IIQ.getMetadata(LI, LLVMContext::MD_nonnull) ||
+          (Q.IIQ.getMetadata(LI, LLVMContext::MD_dereferenceable) &&
+           !NullPointerIsDefined(LI->getFunction(), PtrT->getAddressSpace())))
         return true;
 
     // No need to fall through to computeKnownBits as range metadata is already
     // handled in isKnownNonZero.
     return false;
+  }
   case Instruction::Call:
   case Instruction::Invoke:
     if (I->getType()->isPointerTy()) {
       const auto *Call = cast<CallBase>(I);
       if (Call->isReturnNonNull())
         return true;
       if (const auto *RP = getArgumentAliasingToReturnedPointer(Call, true))
         return isKnownNonZero(RP, Depth, Q);

llvm/test/Transforms/InstSimplify/icmp.ll

 ; CHECK-NEXT:    [[SUB:%.*]] = sub i8 2, [[X:%.*]]
 ; CHECK-NEXT:    [[CMP:%.*]] = icmp ne i8 [[SUB]], [[X]]
 ; CHECK-NEXT:    ret i1 [[CMP]]
 ;
   %sub = sub i8 2, %x
   %cmp = icmp ne i8 %sub, %x
   ret i1 %cmp
 }
+
+define i1 @load_ptr(ptr %p) {
+; CHECK-LABEL: @load_ptr(
+; CHECK-NEXT:    ret i1 true
+;
+  %load_p = load ptr, ptr %p, !dereferenceable !{i64 8}
+  %r = icmp ne ptr %load_p, null
+  ret i1 %r
+}
+
+define i1 @load_ptr_null_valid(ptr %p) null_pointer_is_valid {
+; CHECK-LABEL: @load_ptr_null_valid(
+; CHECK-NEXT:    [[LOAD_P:%.*]] = load ptr, ptr [[P:%.*]], align 8, !dereferenceable !0
+; CHECK-NEXT:    [[R:%.*]] = icmp ne ptr [[LOAD_P]], null
+; CHECK-NEXT:    ret i1 [[R]]
+;
+  %load_p = load ptr, ptr %p, !dereferenceable !{i64 8}
+  %r = icmp ne ptr %load_p, null
+  ret i1 %r
+}