Add a new pass AddReadAttrs which works out which functions

can get the readnone/readonly attributes, and gives them it.
The plan is to remove markmodref (which did the same thing
by querying GlobalsModRef) and delete the analogous
functionality from GlobalsModRef.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@56341 91177308-0d34-0410-b5e6-96231b3b80d8

test/Transforms/AddReadAttrs/2008-09-03-Mutual.ll

@@ -0,0 +1,11 @@
+; RUN: llvm-as < %s | opt -addreadattrs | llvm-dis | grep readnone
+
+define i32 @a() {
+	%tmp = call i32 @b( )		; <i32> [#uses=1]
+	ret i32 %tmp
+}
+
+define i32 @b() {
+	%tmp = call i32 @a( )		; <i32> [#uses=1]
+	ret i32 %tmp
+}

test/Transforms/AddReadAttrs/2008-09-03-ReadNone.ll

@@ -0,0 +1,9 @@
+; RUN: llvm-as < %s | opt -addreadattrs | llvm-dis | grep readnone | count 2
+
+define i32 @f() {
+entry:
+	%tmp = call i32 @e( )		; <i32> [#uses=1]
+	ret i32 %tmp
+}
+
+declare i32 @e() readnone

test/Transforms/AddReadAttrs/2008-09-03-ReadOnly.ll

@@ -0,0 +1,9 @@
+; RUN: llvm-as < %s | opt -addreadattrs | llvm-dis | grep readonly | count 2
+
+define i32 @f() {
+entry:
+	%tmp = call i32 @e( )		; <i32> [#uses=1]
+	ret i32 %tmp
+}
+
+declare i32 @e() readonly

test/Transforms/AddReadAttrs/2008-09-13-VolatileRead.ll

@@ -0,0 +1,9 @@
+; RUN: llvm-as < %s | opt -addreadattrs | llvm-dis | not grep read
+; PR2792
+
+@g = global i32 0		; <i32*> [#uses=1]
+
+define i32 @f() {
+	%t = volatile load i32* @g		; <i32> [#uses=1]
+	ret i32 %t
+}