[DSE] Update dereferenceable attributes when adjusting memintrinsic ptr

llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp

@@ -50,6 +50,7 @@
 #include "llvm/Analysis/TargetLibraryInfo.h"
 #include "llvm/Analysis/ValueTracking.h"
 #include "llvm/IR/Argument.h"
+#include "llvm/IR/AttributeMask.h"
 #include "llvm/IR/BasicBlock.h"
 #include "llvm/IR/Constant.h"
 #include "llvm/IR/ConstantRangeList.h"
@@ -563,6 +564,43 @@ static void shortenAssignment(Instruction *Inst, Value *OriginalDest,
   for_each(LinkedDVRAssigns, InsertAssignForOverlap);
 }
 
+/// Update the attributes given that a memory access is updated (the
+/// dereferenced pointer could be moved forward when shortening a
+/// mem intrinsic).
+static void adjustArgAttributes(AnyMemIntrinsic *Intrinsic, unsigned ArgNo,
+                                uint64_t PtrOffset) {
+  // Remember old attributes.
+  AttributeSet OldAttrs = Intrinsic->getParamAttributes(ArgNo);
+
+  // Find attributes that should be kept, and remove the rest.
+  AttributeMask AttrsToRemove;
+  for (auto &Attr : OldAttrs) {
+    if (Attr.hasKindAsEnum()) {
+      switch (Attr.getKindAsEnum()) {
+      default:
+        break;
+      case Attribute::Alignment:
+        // Only keep alignment if PtrOffset satisfy the alignment.
+        if (isAligned(Attr.getAlignment().valueOrOne(), PtrOffset))
+          continue;
+        break;
+      case Attribute::Dereferenceable:
+      case Attribute::DereferenceableOrNull:
+        // We could reduce the size of these attributes according to
+        // PtrOffset. But we simply drop these for now.
+        break;
+      case Attribute::NonNull:
+      case Attribute::NoUndef:
+        continue;
+      }
+    }
+    AttrsToRemove.addAttribute(Attr);
+  }
+
+  // Remove the attributes that should be dropped.
+  Intrinsic->removeParamAttrs(ArgNo, AttrsToRemove);
+}
+
 static bool tryToShorten(Instruction *DeadI, int64_t &DeadStart,
                          uint64_t &DeadSize, int64_t KillingStart,
                          uint64_t KillingSize, bool IsOverwriteEnd) {
@@ -644,6 +682,7 @@ static bool tryToShorten(Instruction *DeadI, int64_t &DeadStart,
         DeadI->getIterator());
     NewDestGEP->setDebugLoc(DeadIntrinsic->getDebugLoc());
     DeadIntrinsic->setDest(NewDestGEP);
+    adjustArgAttributes(DeadIntrinsic, 0, ToRemoveSize);
   }
 
   // Update attached dbg.assign intrinsics. Assume 8-bit byte.

llvm/test/Transforms/DeadStoreElimination/OverwriteStoreBegin.ll

@@ -402,3 +402,33 @@ entry:
   store i64 1, ptr %p, align 1
   ret void
 }
+
+; Verify that we adjust/drop the dereferenceable attribute.
+define void @dereferenceable(ptr nocapture %p) {
+; CHECK-LABEL: @dereferenceable(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[TMP0:%.*]] = getelementptr inbounds i8, ptr [[P:%.*]], i64 4
+; CHECK-NEXT:    call void @llvm.memset.p0.i64(ptr align 4 [[TMP0]], i8 0, i64 24, i1 false)
+; CHECK-NEXT:    store i32 1, ptr [[P]], align 4
+; CHECK-NEXT:    ret void
+;
+entry:
+  call void @llvm.memset.p0.i64(ptr dereferenceable(28) align 4 %p, i8 0, i64 28, i1 false)
+  store i32 1, ptr %p, align 4
+  ret void
+}
+
+; Verify that we adjust/drop the dereferenceable_or_null attribute.
+define void @dereferenceable_or_null(ptr nocapture %p) {
+; CHECK-LABEL: @dereferenceable_or_null(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[TMP0:%.*]] = getelementptr inbounds i8, ptr [[P:%.*]], i64 8
+; CHECK-NEXT:    call void @llvm.memset.p0.i64(ptr align 4 [[TMP0]], i8 0, i64 20, i1 false)
+; CHECK-NEXT:    store i64 1, ptr [[P]], align 4
+; CHECK-NEXT:    ret void
+;
+entry:
+  call void @llvm.memset.p0.i64(ptr dereferenceable_or_null(28) align 4 %p, i8 0, i64 28, i1 false)
+  store i64 1, ptr %p, align 4
+  ret void
+}