Volatile loads and stores aren't honored

[yvt]

#[no_mangle]
pub unsafe fn assign_answer(x: *mut u32) {
    x.read_volatile();
    x.write_volatile(42);
    x.write_volatile(42);
}

In the code generated by cg_llvm, all volatile loads and stores are preserved.

0000000000001100 <assign_answer>:
    1100:       8b 07                   mov    (%rdi),%eax
    1102:       c7 07 2a 00 00 00       movl   $0x2a,(%rdi)
    1108:       c7 07 2a 00 00 00       movl   $0x2a,(%rdi)
    110e:       c3                      ret    
    110f:       90                      nop

In the code generated by cg_gcc, the load whose result is discarded is eliminated, and the overlapping stores are combined into one.

0000000000001100 <assign_answer>:
    1100:       c7 07 2a 00 00 00       movl   $0x2a,(%rdi)
    1106:       c3                      ret    
    1107:       66 0f 1f 84 00 00 00    nopw   0x0(%rax,%rax,1)
    110e:       00 00 

[yvt]

Looks like the volatile qualification is incorrectly applied to the pointer type instead of its pointee.

rustc_codegen_gcc/src/builder.rs

Lines 671 to 675 in 1d62e95

	fn volatile_load(&mut self, _ty: Type<'gcc>, ptr: RValue<'gcc>) -> RValue<'gcc> {
	// TODO(antoyo): use ty.
	let ptr = self.context.new_cast(None, ptr, ptr.get_type().make_volatile());
	ptr.dereference(None).to_rvalue()
	}