Add support for invariant.start inside the static constructor evaluator. This is

useful to represent a variable that is const in the source but can't be constant
in the IR because of a non-trivial constructor. If globalopt evaluates the
constructor, and there was an invariant.start with no matching invariant.end
possible, it will mark the global constant afterwards.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@150794 91177308-0d34-0410-b5e6-96231b3b80d8

test/Transforms/GlobalOpt/invariant.ll

@@ -0,0 +1,34 @@
+; RUN: opt -globalopt -S -o - < %s | FileCheck %s
+
+declare {}* @llvm.invariant.start(i64 %size, i8* nocapture %ptr)
+
+define void @test1(i8* %ptr) {
+  call {}* @llvm.invariant.start(i64 -1, i8* %ptr)
+  ret void
+}
+
+@object1 = global i32 0
+; CHECK: @object1 = constant i32 -1
+define void @ctor1() {
+  store i32 -1, i32* @object1
+  %A = bitcast i32* @object1 to i8*
+  call void @test1(i8* %A)
+  ret void
+}
+
+
+@object2 = global i32 0
+; CHECK: @object2 = global i32 0
+define void @ctor2() {
+  store i32 -1, i32* @object2
+  %A = bitcast i32* @object2 to i8*
+  %B = call {}* @llvm.invariant.start(i64 -1, i8* %A)
+  ; Why in the world does this pass the verifier?
+  %C = bitcast {}* %B to i8*
+  ret void
+}
+
+@llvm.global_ctors = appending constant
+  [2 x { i32, void ()* }]
+  [ { i32, void ()* } { i32 65535, void ()* @ctor1 },
+    { i32, void ()* } { i32 65535, void ()* @ctor2 } ]