@memset undefined not optimized out

[silversquirl]

Zig Version

0.11.0-dev.960+af9a9a137

Steps to Reproduce and Observed Behavior

// test.zig
export fn foo(x: [*]u8, l: usize) void {
    @memset(x, undefined, l);
}

$ zig build-obj -OReleaseFast test.zig && objdump -d test.o

test.o:     file format elf64-x86-64


Disassembly of section .text:

0000000000000000 <foo>:
   0:	48 89 f2             	mov    %rsi,%rdx
   3:	be aa 00 00 00       	mov    $0xaa,%esi
   8:	e9 00 00 00 00       	jmpq   d <foo+0xd>

Expected Behavior

$ zig build-obj -OReleaseFast test.zig && objdump -d test.o

test.o:     file format elf64-x86-64


Disassembly of section .text:

0000000000000000 <foo>:
   0:	c3                   	retq

[silversquirl]

This is a regression in stage2; -fstage1 in 0.10 emits the desired (lack of) code