diff --git a/llvm/lib/Transforms/Scalar/EarlyCSE.cpp b/llvm/lib/Transforms/Scalar/EarlyCSE.cpp
index cf11f5bc885a7..b8eab9bb18b69 100644
--- a/llvm/lib/Transforms/Scalar/EarlyCSE.cpp
+++ b/llvm/lib/Transforms/Scalar/EarlyCSE.cpp
@@ -362,7 +362,7 @@ static bool isEqualImpl(SimpleValue LHS, SimpleValue RHS) {
 
   if (LHSI->getOpcode() != RHSI->getOpcode())
     return false;
-  if (LHSI->isIdenticalToWhenDefined(RHSI)) {
+  if (LHSI->isIdenticalToWhenDefined(RHSI, /*IntersectAttrs=*/true)) {
     // Convergent calls implicitly depend on the set of threads that is
     // currently executing, so conservatively return false if they are in
     // different basic blocks.
@@ -551,7 +551,7 @@ bool DenseMapInfo<CallValue>::isEqual(CallValue LHS, CallValue RHS) {
   if (LHSI->isConvergent() && LHSI->getParent() != RHSI->getParent())
     return false;
 
-  return LHSI->isIdenticalTo(RHSI);
+  return LHSI->isIdenticalToWhenDefined(RHSI, /*IntersectAttrs=*/true);
 }
 
 //===----------------------------------------------------------------------===//
@@ -1307,6 +1307,23 @@ static void combineIRFlags(Instruction &From, Value *To) {
         (I->hasPoisonGeneratingFlags() && !programUndefinedIfPoison(I)))
       I->andIRFlags(&From);
   }
+  if (isa<CallBase>(&From) && isa<CallBase>(To)) {
+    // NB: Intersection of attrs between InVal.first and Inst is overly
+    // conservative. Since we only CSE readonly functions that have the same
+    // memory state, we can preserve (or possibly in some cases combine)
+    // more attributes. Likewise this implies when checking equality of
+    // callsite for CSEing, we can probably ignore more attributes.
+    // Generally poison generating attributes need to be handled with more
+    // care as they can create *new* UB if preserved/combined and violated.
+    // Attributes that imply immediate UB on the otherhand would have been
+    // violated either way.
+    bool Success =
+        cast<CallBase>(To)->tryIntersectAttributes(cast<CallBase>(&From));
+    assert(Success && "Failed to intersect attributes in callsites that "
+                      "passed identical check");
+    // For NDEBUG Compile.
+    (void)Success;
+  }
 }
 
 bool EarlyCSE::overridingStores(const ParseMemoryInst &Earlier,
@@ -1632,6 +1649,7 @@ bool EarlyCSE::processNode(DomTreeNode *Node) {
           LLVM_DEBUG(dbgs() << "Skipping due to debug counter\n");
           continue;
         }
+        combineIRFlags(Inst, InVal.first);
         if (!Inst.use_empty())
           Inst.replaceAllUsesWith(InVal.first);
         salvageKnowledge(&Inst, &AC);
diff --git a/llvm/test/Transforms/EarlyCSE/replace-calls-def-attrs.ll b/llvm/test/Transforms/EarlyCSE/replace-calls-def-attrs.ll
new file mode 100644
index 0000000000000..2adaf1c7b67a0
--- /dev/null
+++ b/llvm/test/Transforms/EarlyCSE/replace-calls-def-attrs.ll
@@ -0,0 +1,256 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --check-attributes --check-globals all --version 5
+; RUN: opt -S -passes=early-cse  < %s | FileCheck %s
+
+declare i8 @baz(i8, i8)
+declare i8 @baz_side_effects(i8, i8)
+declare i8 @buz(i8, i8)
+
+declare ptr @baz.ptr(i8, i8)
+declare i8 @buz.ptr(ptr, ptr)
+
+declare float @baz.fp(float, float)
+declare i8 @buz.fp(float, float)
+define i8 @same_parent_combine_diff_attrs(i8 %x, i8 %y) {
+; CHECK-LABEL: define i8 @same_parent_combine_diff_attrs(
+; CHECK-SAME: i8 [[X:%.*]], i8 [[Y:%.*]]) {
+; CHECK-NEXT:    [[C1:%.*]] = call i8 @baz(i8 [[X]], i8 noundef [[Y]]) #[[ATTR0:[0-9]+]]
+; CHECK-NEXT:    [[R:%.*]] = call i8 @buz(i8 [[C1]], i8 [[C1]])
+; CHECK-NEXT:    ret i8 [[R]]
+;
+  %c1 = call i8 @baz(i8 noundef %x, i8 noundef %y) readnone
+  %c0 = call i8 @baz(i8 %x, i8 noundef %y) readnone
+  %r = call i8 @buz(i8 %c0, i8 %c1)
+  ret i8 %r
+
+}
+
+define i8 @same_parent_combine_diff_attrs_needs_intersect(i8 %x, i8 %y) {
+; CHECK-LABEL: define i8 @same_parent_combine_diff_attrs_needs_intersect(
+; CHECK-SAME: i8 [[X:%.*]], i8 [[Y:%.*]]) {
+; CHECK-NEXT:    [[C1:%.*]] = call ptr @baz.ptr(i8 [[X]], i8 noundef [[Y]]) #[[ATTR0]]
+; CHECK-NEXT:    [[R:%.*]] = call i8 @buz.ptr(ptr [[C1]], ptr [[C1]])
+; CHECK-NEXT:    ret i8 [[R]]
+;
+  %c1 = call nonnull ptr @baz.ptr(i8 noundef %x, i8 noundef %y) readnone
+  %c0 = call ptr @baz.ptr(i8 %x, i8 noundef %y) readnone
+  %r = call i8 @buz.ptr(ptr %c0, ptr %c1)
+  ret i8 %r
+
+}
+
+define i8 @same_parent_combine_diff_attrs_fmf(float %x, float %y) {
+; CHECK-LABEL: define i8 @same_parent_combine_diff_attrs_fmf(
+; CHECK-SAME: float [[X:%.*]], float [[Y:%.*]]) {
+; CHECK-NEXT:    [[C1:%.*]] = call nnan float @baz.fp(float [[X]], float noundef [[Y]]) #[[ATTR1:[0-9]+]]
+; CHECK-NEXT:    [[R:%.*]] = call i8 @buz.fp(float [[C1]], float [[C1]])
+; CHECK-NEXT:    ret i8 [[R]]
+;
+  %c1 = call nnan nsz float @baz.fp(float noundef %x, float noundef %y) readonly
+  %c0 = call nnan float @baz.fp(float %x, float noundef %y) readonly
+  %r = call i8 @buz.fp(float %c0, float %c1)
+  ret i8 %r
+
+}
+
+define i8 @same_parent_combine_diff_attrs_fmf2(float %x, float %y) {
+; CHECK-LABEL: define i8 @same_parent_combine_diff_attrs_fmf2(
+; CHECK-SAME: float [[X:%.*]], float [[Y:%.*]]) {
+; CHECK-NEXT:    [[C1:%.*]] = call nnan float @baz.fp(float [[X]], float noundef [[Y]]) #[[ATTR0]]
+; CHECK-NEXT:    [[R:%.*]] = call i8 @buz.fp(float [[C1]], float [[C1]])
+; CHECK-NEXT:    ret i8 [[R]]
+;
+  %c1 = call nnan float @baz.fp(float noundef %x, float noundef %y) readnone
+  %c0 = call nnan nsz float @baz.fp(float %x, float noundef %y) readnone
+  %r = call i8 @buz.fp(float %c0, float %c1)
+  ret i8 %r
+
+}
+
+define i8 @same_parent_combine_diff_attrs_needs_intersect2(i8 %x, i8 %y) {
+; CHECK-LABEL: define i8 @same_parent_combine_diff_attrs_needs_intersect2(
+; CHECK-SAME: i8 [[X:%.*]], i8 [[Y:%.*]]) {
+; CHECK-NEXT:    [[C1:%.*]] = call ptr @baz.ptr(i8 [[X]], i8 noundef [[Y]]) #[[ATTR1]]
+; CHECK-NEXT:    [[R:%.*]] = call i8 @buz.ptr(ptr [[C1]], ptr [[C1]])
+; CHECK-NEXT:    ret i8 [[R]]
+;
+  %c1 = call nonnull ptr @baz.ptr(i8 noundef %x, i8 noundef %y) readonly
+  %c0 = call ptr @baz.ptr(i8 %x, i8 noundef %y) readonly
+  %r = call i8 @buz.ptr(ptr %c0, ptr %c1)
+  ret i8 %r
+
+}
+
+define i8 @same_parent_combine_diff_attrs_really_needs_intersect(i8 %x, i8 %y) {
+; CHECK-LABEL: define i8 @same_parent_combine_diff_attrs_really_needs_intersect(
+; CHECK-SAME: i8 [[X:%.*]], i8 [[Y:%.*]]) {
+; CHECK-NEXT:    [[C1:%.*]] = call ptr @baz.ptr(i8 [[X]], i8 noundef [[Y]]) #[[ATTR1]]
+; CHECK-NEXT:    [[R:%.*]] = call i8 @buz.ptr(ptr [[C1]], ptr noundef [[C1]])
+; CHECK-NEXT:    ret i8 [[R]]
+;
+  %c1 = call nonnull ptr @baz.ptr(i8 noundef %x, i8 noundef %y) readonly
+  %c0 = call ptr @baz.ptr(i8 %x, i8 noundef %y) readonly
+  %r = call i8 @buz.ptr(ptr %c0, ptr noundef %c1)
+  ret i8 %r
+
+}
+
+define i8 @same_parent_combine_diff_attrs_fail_side_effects(i8 %x, i8 %y) {
+; CHECK-LABEL: define i8 @same_parent_combine_diff_attrs_fail_side_effects(
+; CHECK-SAME: i8 [[X:%.*]], i8 [[Y:%.*]]) {
+; CHECK-NEXT:    [[C1:%.*]] = call i8 @baz(i8 noundef [[X]], i8 noundef [[Y]])
+; CHECK-NEXT:    [[C0:%.*]] = call i8 @baz(i8 [[X]], i8 noundef [[Y]])
+; CHECK-NEXT:    [[R:%.*]] = call i8 @buz(i8 [[C0]], i8 [[C1]])
+; CHECK-NEXT:    ret i8 [[R]]
+;
+  %c1 = call i8 @baz(i8 noundef %x, i8 noundef %y)
+  %c0 = call i8 @baz(i8 %x, i8 noundef %y)
+  %r = call i8 @buz(i8 %c0, i8 %c1)
+  ret i8 %r
+
+}
+
+define i8 @same_parent_combine_diff_attrs_quasi_side_effects2(i8 %x, i8 %y) {
+; CHECK-LABEL: define i8 @same_parent_combine_diff_attrs_quasi_side_effects2(
+; CHECK-SAME: i8 [[X:%.*]], i8 [[Y:%.*]]) {
+; CHECK-NEXT:    [[C1:%.*]] = call i8 @baz(i8 noundef [[X]], i8 noundef [[Y]]) #[[ATTR0]]
+; CHECK-NEXT:    [[C0:%.*]] = call i8 @baz(i8 [[X]], i8 noundef [[Y]])
+; CHECK-NEXT:    [[R:%.*]] = call i8 @buz(i8 [[C0]], i8 [[C1]])
+; CHECK-NEXT:    ret i8 [[R]]
+;
+  %c1 = call i8 @baz(i8 noundef %x, i8 noundef %y) readnone
+  %c0 = call i8 @baz(i8 %x, i8 noundef %y)
+  %r = call i8 @buz(i8 %c0, i8 %c1)
+  ret i8 %r
+
+}
+
+define i8 @diff_parent_combine_diff_attrs(i1 %c, i8 %x, i8 %y) {
+; CHECK-LABEL: define i8 @diff_parent_combine_diff_attrs(
+; CHECK-SAME: i1 [[C:%.*]], i8 [[X:%.*]], i8 [[Y:%.*]]) {
+; CHECK-NEXT:    [[C1:%.*]] = call i8 @baz(i8 [[X]], i8 noundef [[Y]]) #[[ATTR0]]
+; CHECK-NEXT:    br i1 [[C]], label %[[T:.*]], label %[[F:.*]]
+; CHECK:       [[T]]:
+; CHECK-NEXT:    [[C0:%.*]] = call i8 @baz(i8 noundef [[X]], i8 noundef [[Y]]) #[[ATTR1]]
+; CHECK-NEXT:    [[R:%.*]] = call i8 @buz(i8 [[C0]], i8 [[C1]])
+; CHECK-NEXT:    ret i8 [[R]]
+; CHECK:       [[F]]:
+; CHECK-NEXT:    [[R2:%.*]] = add i8 [[C1]], 4
+; CHECK-NEXT:    ret i8 [[R2]]
+;
+  %c1 = call i8 @baz(i8 %x, i8 noundef %y) readnone
+  br i1 %c, label %T, label %F
+T:
+  %c0 = call i8 @baz(i8 noundef %x, i8 noundef %y) readonly
+  %r = call i8 @buz(i8 %c0, i8 %c1)
+  ret i8 %r
+F:
+  %r2 = add i8 %c1, 4
+  ret i8 %r2
+}
+
+define i8 @diff_parent_combine_diff_attrs_preserves_return_attrs(i1 %c, i8 %x, i8 %y) {
+; CHECK-LABEL: define i8 @diff_parent_combine_diff_attrs_preserves_return_attrs(
+; CHECK-SAME: i1 [[C:%.*]], i8 [[X:%.*]], i8 [[Y:%.*]]) {
+; CHECK-NEXT:    [[C1:%.*]] = call nonnull ptr @baz.ptr(i8 [[X]], i8 noundef [[Y]]) #[[ATTR1]]
+; CHECK-NEXT:    br i1 [[C]], label %[[T:.*]], label %[[F:.*]]
+; CHECK:       [[T]]:
+; CHECK-NEXT:    [[R:%.*]] = call i8 @buz.ptr(ptr [[C1]], ptr noundef [[C1]])
+; CHECK-NEXT:    ret i8 [[R]]
+; CHECK:       [[F]]:
+; CHECK-NEXT:    ret i8 9
+;
+  %c1 = call nonnull ptr @baz.ptr(i8 %x, i8 noundef %y) readonly
+  br i1 %c, label %T, label %F
+T:
+  %c0 = call nonnull ptr @baz.ptr(i8 noundef %x, i8 noundef %y) readonly
+  %r = call i8 @buz.ptr(ptr %c0, ptr noundef %c1)
+  ret i8 %r
+F:
+  ret i8 9
+}
+
+define i8 @same_parent_combine_diff_attrs_todo(i8 %x, i8 %y) {
+; CHECK-LABEL: define i8 @same_parent_combine_diff_attrs_todo(
+; CHECK-SAME: i8 [[X:%.*]], i8 [[Y:%.*]]) {
+; CHECK-NEXT:    [[C1:%.*]] = call i8 @baz(i8 [[X]], i8 noundef [[Y]]) #[[ATTR0]]
+; CHECK-NEXT:    [[C0:%.*]] = call i8 @baz(i8 noundef [[X]], i8 noundef [[Y]]) #[[ATTR2:[0-9]+]]
+; CHECK-NEXT:    [[R:%.*]] = call i8 @buz(i8 [[C0]], i8 [[C1]])
+; CHECK-NEXT:    ret i8 [[R]]
+;
+  %c1 = call i8 @baz(i8 %x, i8 noundef %y) readnone
+  %c0 = call i8 @baz(i8 noundef %x, i8 noundef %y) readnone alwaysinline
+  %r = call i8 @buz(i8 %c0, i8 %c1)
+  ret i8 %r
+
+}
+
+define i8 @same_parent_combine_diff_attrs_fail(i8 %x, i8 %y) {
+; CHECK-LABEL: define i8 @same_parent_combine_diff_attrs_fail(
+; CHECK-SAME: i8 [[X:%.*]], i8 [[Y:%.*]]) {
+; CHECK-NEXT:    [[C1:%.*]] = call i8 @baz(i8 [[X]], i8 noundef [[Y]]) #[[ATTR0]]
+; CHECK-NEXT:    [[C0:%.*]] = call i8 @baz(i8 noundef [[X]], i8 noundef [[Y]]) #[[ATTR3:[0-9]+]]
+; CHECK-NEXT:    [[R:%.*]] = call i8 @buz(i8 [[C0]], i8 [[C1]])
+; CHECK-NEXT:    ret i8 [[R]]
+;
+  %c1 = call i8 @baz(i8 %x, i8 noundef %y) readnone
+  %c0 = call i8 @baz(i8 noundef %x, i8 noundef %y) readnone strictfp
+  %r = call i8 @buz(i8 %c0, i8 %c1)
+  ret i8 %r
+
+}
+
+define i8 @diff_parent_combine_diff_attrs_todo(i1 %c, i8 %x, i8 %y) {
+; CHECK-LABEL: define i8 @diff_parent_combine_diff_attrs_todo(
+; CHECK-SAME: i1 [[C:%.*]], i8 [[X:%.*]], i8 [[Y:%.*]]) {
+; CHECK-NEXT:    [[C1:%.*]] = call i8 @baz(i8 [[X]], i8 noundef [[Y]]) #[[ATTR0]]
+; CHECK-NEXT:    br i1 [[C]], label %[[T:.*]], label %[[F:.*]]
+; CHECK:       [[T]]:
+; CHECK-NEXT:    [[C0:%.*]] = call i8 @baz(i8 noundef [[X]], i8 noundef [[Y]]) #[[ATTR4:[0-9]+]]
+; CHECK-NEXT:    [[R:%.*]] = call i8 @buz(i8 [[C0]], i8 [[C1]])
+; CHECK-NEXT:    ret i8 [[R]]
+; CHECK:       [[F]]:
+; CHECK-NEXT:    [[R2:%.*]] = add i8 [[C1]], 4
+; CHECK-NEXT:    ret i8 [[R2]]
+;
+  %c1 = call i8 @baz(i8 %x, i8 noundef %y) readnone
+  br i1 %c, label %T, label %F
+T:
+  %c0 = call i8 @baz(i8 noundef %x, i8 noundef %y) readnone optnone noinline
+  %r = call i8 @buz(i8 %c0, i8 %c1)
+  ret i8 %r
+F:
+  %r2 = add i8 %c1, 4
+  ret i8 %r2
+}
+
+define i8 @diff_parent_combine_diff_attrs_fail(i1 %c, i8 %x, i8 %y) {
+; CHECK-LABEL: define i8 @diff_parent_combine_diff_attrs_fail(
+; CHECK-SAME: i1 [[C:%.*]], i8 [[X:%.*]], i8 [[Y:%.*]]) {
+; CHECK-NEXT:    [[C1:%.*]] = call i8 @baz(i8 [[X]], i8 noundef [[Y]]) #[[ATTR0]]
+; CHECK-NEXT:    br i1 [[C]], label %[[T:.*]], label %[[F:.*]]
+; CHECK:       [[T]]:
+; CHECK-NEXT:    [[C0:%.*]] = call i8 @baz(i8 noundef [[X]], i8 noundef [[Y]]) #[[ATTR3]]
+; CHECK-NEXT:    [[R:%.*]] = call i8 @buz(i8 [[C0]], i8 [[C1]])
+; CHECK-NEXT:    ret i8 [[R]]
+; CHECK:       [[F]]:
+; CHECK-NEXT:    [[R2:%.*]] = add i8 [[C1]], 4
+; CHECK-NEXT:    ret i8 [[R2]]
+;
+  %c1 = call i8 @baz(i8 %x, i8 noundef %y) readnone
+  br i1 %c, label %T, label %F
+T:
+  %c0 = call i8 @baz(i8 noundef %x, i8 noundef %y) readnone strictfp
+  %r = call i8 @buz(i8 %c0, i8 %c1)
+  ret i8 %r
+F:
+  %r2 = add i8 %c1, 4
+  ret i8 %r2
+}
+
+;.
+; CHECK: attributes #[[ATTR0]] = { memory(none) }
+; CHECK: attributes #[[ATTR1]] = { memory(read) }
+; CHECK: attributes #[[ATTR2]] = { alwaysinline memory(none) }
+; CHECK: attributes #[[ATTR3]] = { strictfp memory(none) }
+; CHECK: attributes #[[ATTR4]] = { noinline optnone memory(none) }
+;.