Index: lib/Transforms/IPO/FunctionAttrs.cpp
===================================================================
--- lib/Transforms/IPO/FunctionAttrs.cpp
+++ lib/Transforms/IPO/FunctionAttrs.cpp
@@ -205,6 +205,11 @@
       // No change.
       continue;
 
+    if (F->getIntrinsicID() == Intrinsic::assume)
+      // don't change attributes of the assume intrinsic, 
+      // so that later on, it is not thrown away by other optimizations
+      continue;
+
     MadeChange = true;
 
     // Clear out any existing attributes.
Index: test/Transforms/FunctionAttrs/assume.ll
===================================================================
--- test/Transforms/FunctionAttrs/assume.ll
+++ test/Transforms/FunctionAttrs/assume.ll
@@ -0,0 +1,29 @@
+; RUN: opt -functionattrs -S < %s | FileCheck %s
+; RUN: opt -functionattrs -instcombine -S < %s | FileCheck %s -check-prefix=ASSUME
+;
+; Ensures that llvm.assume:
+;  is not marked with readnone attribute.
+;  is not considered as accessing memory for the purposes of function attributes computation.
+
+;CHECK: declare void @llvm.assume(i1) #0
+declare void @llvm.assume(i1)
+
+;CHECK: define i32 @foo(i32 %x) #1
+;ASSUME: define i32 @foo(i32 %x)
+define i32 @foo(i32 %x) {
+entry:
+  %cmp = icmp eq i32 %x, 2
+  call void @llvm.assume(i1 %cmp)
+;ASSUME: ret i32 2
+  ret i32 %x
+}
+
+;CHECK: define i32 @foo2(i32 %x) #1
+define i32 @foo2(i32 %x) {
+entry:
+  %foo.x = call i32 @foo(i32 %x)
+  ret i32 %foo.x
+}
+
+;CHECK: attributes #0 = { nounwind }
+;CHECK: attributes #1 = { readnone }