rustc_codegen_llvm: give names to non-alloca variable values.

src/test/codegen/var-names.rs

@@ -0,0 +1,15 @@
+// compile-flags: -O -C no-prepopulate-passes
+
+#![crate_type = "lib"]
+
+// CHECK-LABEL: define i32 @test(i32 %a, i32 %b)
+#[no_mangle]
+pub fn test(a: u32, b: u32) -> u32 {
+    let c = a + b;
+    // CHECK: %c = add i32 %a, %b
+    let d = c;
+    let e = d * a;
+    // CHECK-NEXT: %e = mul i32 %c, %a
+    e
+    // CHECK-NEXT: ret i32 %e
+}