[JumpThreading] Add test with free instructions (NFC)

Which demonstrates that "free" instructions can prevent jump
threading.

llvm/test/Transforms/JumpThreading/free_instructions.ll

@@ -0,0 +1,64 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt -S -jump-threading -jump-threading-threshold=3 < %s | FileCheck %s
+
+; TODO: In this test case, only the stores in %join should cound towards
+; the jump threading threshold, as everything else are free instructions.
+define i32 @free_instructions(i1 %c, i32* %p) {
+; CHECK-LABEL: @free_instructions(
+; CHECK-NEXT:    br i1 [[C:%.*]], label [[IF:%.*]], label [[ELSE:%.*]]
+; CHECK:       if:
+; CHECK-NEXT:    store i32 -1, i32* [[P:%.*]], align 4
+; CHECK-NEXT:    br label [[JOIN:%.*]]
+; CHECK:       else:
+; CHECK-NEXT:    store i32 -2, i32* [[P]], align 4
+; CHECK-NEXT:    br label [[JOIN]]
+; CHECK:       join:
+; CHECK-NEXT:    call void @llvm.experimental.noalias.scope.decl(metadata [[META0:![0-9]+]])
+; CHECK-NEXT:    store i32 1, i32* [[P]], align 4, !noalias !0
+; CHECK-NEXT:    call void @llvm.assume(i1 true) [ "align"(i32* [[P]], i64 32) ]
+; CHECK-NEXT:    store i32 2, i32* [[P]], align 4
+; CHECK-NEXT:    [[P2:%.*]] = bitcast i32* [[P]] to i8*
+; CHECK-NEXT:    [[P3:%.*]] = call i8* @llvm.launder.invariant.group.p0i8(i8* [[P2]])
+; CHECK-NEXT:    [[P4:%.*]] = bitcast i8* [[P3]] to i32*
+; CHECK-NEXT:    store i32 3, i32* [[P4]], align 4, !invariant.group !3
+; CHECK-NEXT:    br i1 [[C]], label [[IF2:%.*]], label [[ELSE2:%.*]]
+; CHECK:       if2:
+; CHECK-NEXT:    ret i32 0
+; CHECK:       else2:
+; CHECK-NEXT:    ret i32 1
+;
+  br i1 %c, label %if, label %else
+
+if:
+  store i32 -1, i32* %p
+  br label %join
+
+else:
+  store i32 -2, i32* %p
+  br label %join
+
+join:
+  call void @llvm.experimental.noalias.scope.decl(metadata !0)
+  store i32 1, i32* %p, !noalias !0
+  call void @llvm.assume(i1 true) ["align"(i32* %p, i64 32)]
+  store i32 2, i32* %p
+  %p2 = bitcast i32* %p to i8*
+  %p3 = call i8* @llvm.launder.invariant.group.p0i8(i8* %p2)
+  %p4 = bitcast i8* %p3 to i32*
+  store i32 3, i32* %p4, !invariant.group !{}
+  br i1 %c, label %if2, label %else2
+
+if2:
+  ret i32 0
+
+else2:
+  ret i32 1
+}
+
+declare void @llvm.assume(i1)
+declare void @llvm.experimental.noalias.scope.decl(metadata)
+declare i8* @llvm.launder.invariant.group.p0i8(i8*)
+
+!0 = !{!1}
+!1 = distinct !{!1, !2, !"scope"}
+!2 = distinct !{!2, !"domain"}