[Attributor][FIX] Do not derive nonnull and dereferenceable w/o access

An inbounds GEP results in poison if the value is not "inbounds", not in
UB. We accidentally derived nonnull and dereferenceable from these
inbounds GEPs even in the absence of accesses that would make the poison
to UB.

Author: jdoerfert

llvm/lib/Transforms/IPO/Attributor.cpp

@@ -1792,20 +1792,6 @@ static int64_t getKnownNonNullAndDerefBytesForUse(
       return std::max(int64_t(0), DerefBytes);
     }
   }
-  if (const Value *Base =
-          GetPointerBaseWithConstantOffset(UseV, Offset, DL,
-                                           /*AllowNonInbounds*/ false)) {
-    if (Base == &AssociatedValue) {
-      // As long as we only use known information there is no need to track
-      // dependences here.
-      auto &DerefAA = A.getAAFor<AADereferenceable>(
-          QueryingAA, IRPosition::value(*Base), /* TrackDependence */ false);
-      IsNonNull |= (!NullPointerIsDefined && DerefAA.isKnownNonNull());
-      IsNonNull |= (!NullPointerIsDefined && (Offset != 0));
-      int64_t DerefBytes = DerefAA.getKnownDereferenceableBytes();
-      return std::max(int64_t(0), DerefBytes - std::max(int64_t(0), Offset));
-    }
-  }
 
   return 0;
 }

llvm/test/Transforms/Attributor/dereferenceable-1.ll

@@ -30,7 +30,7 @@ define i32* @test3_1(i32* dereferenceable(8) %0) local_unnamed_addr {
 }
 
 define i32* @test3_2(i32* dereferenceable_or_null(32) %0) local_unnamed_addr {
-; ATTRIBUTOR: define nonnull dereferenceable(16) i32* @test3_2(i32* nofree nonnull readnone dereferenceable(32) "no-capture-maybe-returned" %0)
+; ATTRIBUTOR: define nonnull dereferenceable(16) i32* @test3_2(i32* nofree readnone dereferenceable_or_null(32) "no-capture-maybe-returned" %0)
   %ret = getelementptr inbounds i32, i32* %0, i64 4
   ret i32* %ret
 }

llvm/test/Transforms/Attributor/nocapture-1.ll

@@ -288,15 +288,15 @@ define i1 @captureICmpRev(i32* %x) {
   ret i1 %1
 }
 
-; ATTRIBUTOR: define i1 @nocaptureInboundsGEPICmp(i32* nocapture nofree nonnull readnone %x)
+; ATTRIBUTOR: define i1 @nocaptureInboundsGEPICmp(i32* nocapture nofree readnone %x)
 define i1 @nocaptureInboundsGEPICmp(i32* %x) {
   %1 = getelementptr inbounds i32, i32* %x, i32 5
   %2 = bitcast i32* %1 to i8*
   %3 = icmp eq i8* %2, null
   ret i1 %3
 }
 
-; ATTRIBUTOR: define i1 @nocaptureInboundsGEPICmpRev(i32* nocapture nofree nonnull readnone %x)
+; ATTRIBUTOR: define i1 @nocaptureInboundsGEPICmpRev(i32* nocapture nofree readnone %x)
 define i1 @nocaptureInboundsGEPICmpRev(i32* %x) {
   %1 = getelementptr inbounds i32, i32* %x, i32 5
   %2 = bitcast i32* %1 to i8*

llvm/test/Transforms/Attributor/nonnull.ll

@@ -817,5 +817,24 @@ define void @PR43833_simple(i32* %0, i32 %1) {
   br i1 %11, label %7, label %8
 }
 
+declare i8* @strrchr(i8* %0, i32 %1) nofree nounwind readonly
+
+; We should not mark the return of @strrchr as `nonnull`, it may well be NULL!
+define i8* @mybasename(i8* nofree readonly %str) {
+; ATTRIBUTOR-LABEL: define {{[^@]+}}@mybasename
+; ATTRIBUTOR-SAME: (i8* nofree readonly [[STR:%.*]])
+; ATTRIBUTOR-NEXT:    [[CALL:%.*]] = call i8* @strrchr(i8* nofree readonly [[STR]], i32 47)
+; ATTRIBUTOR-NEXT:    [[TOBOOL:%.*]] = icmp ne i8* [[CALL]], null
+; ATTRIBUTOR-NEXT:    [[ADD_PTR:%.*]] = getelementptr inbounds i8, i8* [[CALL]], i64 1
+; ATTRIBUTOR-NEXT:    [[COND:%.*]] = select i1 [[TOBOOL]], i8* [[ADD_PTR]], i8* [[STR]]
+; ATTRIBUTOR-NEXT:    ret i8* [[COND]]
+;
+  %call = call i8* @strrchr(i8* %str, i32 47)
+  %tobool = icmp ne i8* %call, null
+  %add.ptr = getelementptr inbounds i8, i8* %call, i64 1
+  %cond = select i1 %tobool, i8* %add.ptr, i8* %str
+  ret i8* %cond
+}
+
 attributes #0 = { "null-pointer-is-valid"="true" }
 attributes #1 = { nounwind willreturn}

llvm/test/Transforms/Attributor/nosync.ll

@@ -25,7 +25,7 @@ target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
 %struct.ST = type { i32, double, %struct.RT }
 
 ; ATTRIBUTOR: Function Attrs: nofree nosync nounwind optsize readnone ssp uwtable
-; ATTRIBUTOR-NEXT: define nonnull i32* @foo(%struct.ST* nofree nonnull readnone "no-capture-maybe-returned" %s)
+; ATTRIBUTOR-NEXT: define nonnull i32* @foo(%struct.ST* nofree readnone "no-capture-maybe-returned" %s)
 define i32* @foo(%struct.ST* %s) nounwind uwtable readnone optsize ssp {
 entry:
   %arrayidx = getelementptr inbounds %struct.ST, %struct.ST* %s, i64 1, i32 2, i32 1, i64 5, i64 13