Don't use global initializer if type does not match

This was relying on the presence of a bitcast to avoid using the
constant global initializer for a load using a different type.
With opaque pointers, we need to check this explicitly.

Author: nikic

compiler/rustc_codegen_llvm/src/builder.rs

@@ -509,15 +509,20 @@ impl<'a, 'll, 'tcx> BuilderMethods<'a, 'tcx> for Builder<'a, 'll, 'tcx> {
             OperandValue::Ref(place.llval, Some(llextra), place.align)
         } else if place.layout.is_llvm_immediate() {
             let mut const_llval = None;
+            let llty = place.layout.llvm_type(self);
             unsafe {
                 if let Some(global) = llvm::LLVMIsAGlobalVariable(place.llval) {
                     if llvm::LLVMIsGlobalConstant(global) == llvm::True {
-                        const_llval = llvm::LLVMGetInitializer(global);
+                        if let Some(init) = llvm::LLVMGetInitializer(global) {
+                            if self.val_ty(init) == llty {
+                                const_llval = Some(init);
+                            }
+                        }
                     }
                 }
             }
             let llval = const_llval.unwrap_or_else(|| {
-                let load = self.load(place.layout.llvm_type(self), place.llval, place.align);
+                let load = self.load(llty, place.llval, place.align);
                 if let abi::Abi::Scalar(scalar) = place.layout.abi {
                     scalar_load_metadata(self, load, scalar, place.layout, Size::ZERO);
                 }