[ValueTracking] Dereferenceable ret attributes implys noundef

[nikic]

LGTM

llvm/lib/Analysis/ValueTracking.cpp

static bool isGuaranteedNotToBeUndefOrPoison(const Value *V,
 
   if (auto *Opr = dyn_cast<Operator>(V)) {
     // If the value is a freeze instruction, then it can never
     // be undef or poison.
     if (isa<FreezeInst>(V))
       return true;
 
     if (const auto *CB = dyn_cast<CallBase>(V)) {
-      if (CB->hasRetAttr(Attribute::NoUndef))
+      if (CB->hasRetAttr(Attribute::NoUndef) ||
+          CB->hasRetAttr(Attribute::Dereferenceable) ||
+          CB->hasRetAttr(Attribute::DereferenceableOrNull))
         return true;
     }
 
     if (const auto *PN = dyn_cast<PHINode>(V)) {
       unsigned Num = PN->getNumIncomingValues();
       bool IsWellDefined = true;
       for (unsigned i = 0; i < Num; ++i) {
         auto *TI = PN->getIncomingBlock(i)->getTerminator();

llvm/test/Transforms/Attributor/memory_locations.ll

 }
 
 define dso_local ptr @internal_argmem_only_write(ptr %arg) {
 ; CHECK: Function Attrs: memory(argmem: readwrite, inaccessiblemem: readwrite)
 ; CHECK-LABEL: define {{[^@]+}}@internal_argmem_only_write
 ; CHECK-SAME: (ptr nocapture nofree noundef nonnull writeonly align 4 dereferenceable(4) [[ARG:%.*]]) #[[ATTR1]] {
 ; CHECK-NEXT:  entry:
 ; CHECK-NEXT:    store i32 10, ptr [[ARG]], align 4
-; CHECK-NEXT:    [[CALL:%.*]] = call noalias dereferenceable_or_null(10) ptr @malloc(i64 noundef 10)
+; CHECK-NEXT:    [[CALL:%.*]] = call noalias noundef dereferenceable_or_null(10) ptr @malloc(i64 noundef 10)
 ; CHECK-NEXT:    ret ptr [[CALL]]
 ;
 entry:
   store i32 10, ptr %arg, align 4
   %call = call dereferenceable_or_null(10) ptr @malloc(i64 10)
   ret ptr %call
 }