Sema: missed simplifications of OPVs

[jacobly0]

const std = @import("std");
pub const Panic = struct {
    pub fn call(_: []const u8, _: ?*std.builtin.StackTrace, _: ?usize) noreturn {
        @trap();
    }
    pub fn sentinelMismatch(expected: anytype, _: @TypeOf(expected)) noreturn {
        @trap();
    }
    pub fn unwrapError(_: ?*std.builtin.StackTrace, _: anyerror) noreturn {
        @trap();
    }
    pub fn outOfBounds(_: usize, _: usize) noreturn {
        @trap();
    }
    pub fn startGreaterThanEnd(_: usize, _: usize) noreturn {
        @trap();
    }
    pub fn inactiveUnionField(active: anytype, _: @TypeOf(active)) noreturn {
        @trap();
    }
    pub const messages = std.debug.FormattedPanic.messages;
};
fn ptrAddr(ptr: [*]const void, index: usize) *const void {
    return &ptr[index];
}
fn ptrAccess(ptr: [*]const void, index: usize) void {
    return ptr[index];
}
fn sliceAddr(slice: []const void, index: usize) *const void {
    return &slice[index];
}
fn sliceAccess(slice: []const void, index: usize) void {
    return slice[index];
}
fn unionInit(val: u8) union(enum) { val: u8 } {
    return .{ .val = val };
}
fn unionAccess(val: union(enum(u1)) { only }) void {
    return val.only;
}
comptime {
    _ = .{ &ptrAddr, &ptrAccess, &sliceAddr, &sliceAccess, &unionInit, &unionAccess };
}

$ zig build-obj repro.zig --verbose-air -fstrip
# Begin Function AIR: repro.ptrAddr:
# Total AIR+Liveness bytes: 232B
# AIR Instructions:         8 (72B)
# AIR Extra Data:           12 (48B)
# Liveness tomb_bits:       8B
# Liveness Extra Data:      0 (0B)
# Liveness special table:   0 (0B)
  %0 = arg([*]const void)
  %1 = arg(usize)
  %2 = alloc(*[*]const void)
  %3!= store_safe(%2, %0!)
  %4 = bitcast(*const [*]const void, %2!)
  %5 = load([*]const void, %4!)
  %6 = ptr_elem_ptr(*const void, %5!, %1!)
  %7!= ret_safe(%6!)
# End Function AIR: repro.ptrAddr

# Begin Function AIR: repro.ptrAccess:
# Total AIR+Liveness bytes: 172B
# AIR Instructions:         4 (36B)
# AIR Extra Data:           6 (24B)
# Liveness tomb_bits:       8B
# Liveness Extra Data:      0 (0B)
# Liveness special table:   0 (0B)
  %0 = arg([*]const void)
  %1 = arg(usize)
  %2 = ptr_elem_val(%0!, %1!)
  %3!= ret_safe(%2!)
# End Function AIR: repro.ptrAccess

# Begin Function AIR: repro.sliceAddr:
# Total AIR+Liveness bytes: 395B
# AIR Instructions:         15 (135B)
# AIR Extra Data:           26 (104B)
# Liveness tomb_bits:       8B
# Liveness Extra Data:      7 (28B)
# Liveness special table:   2 (16B)
  %0 = arg([]const void)
  %1 = arg(usize)
  %2 = alloc(*[]const void)
  %3!= store_safe(%2, %0!)
  %4 = bitcast(*const []const void, %2!)
  %5 = load([]const void, %4!)
  %6 = slice_len(usize, %5)
  %7 = cmp_lt(%1, %6)
  %10!= block(void, {
    %11!= cond_br(%7!, likely {
      %6!
      %12!= br(%10, @Air.Inst.Ref.void_value)
    }, cold {
      %5!
      %8!= call(<fn (usize, usize) noreturn, (function 'outOfBounds')>, [%1!, %6!])
      %9!= unreach()
    })
  } %7! %6!)
  %13 = slice_elem_ptr(*const void, %5!, %1!)
  %14!= ret_safe(%13!)
# End Function AIR: repro.sliceAddr

# Begin Function AIR: repro.sliceAccess:
# Total AIR+Liveness bytes: 335B
# AIR Instructions:         11 (99B)
# AIR Extra Data:           20 (80B)
# Liveness tomb_bits:       8B
# Liveness Extra Data:      7 (28B)
# Liveness special table:   2 (16B)
  %0 = arg([]const void)
  %1 = arg(usize)
  %2 = slice_len(usize, %0)
  %3 = cmp_lt(%1, %2)
  %6!= block(void, {
    %7!= cond_br(%3!, likely {
      %2!
      %8!= br(%6, @Air.Inst.Ref.void_value)
    }, cold {
      %0!
      %4!= call(<fn (usize, usize) noreturn, (function 'outOfBounds')>, [%1!, %2!])
      %5!= unreach()
    })
  } %2! %3!)
  %9 = slice_elem_val(%0!, %1!)
  %10!= ret_safe(%9!)
# End Function AIR: repro.sliceAccess

# Begin Function AIR: repro.unionInit:
# Total AIR+Liveness bytes: 198B
# AIR Instructions:         6 (54B)
# AIR Extra Data:           8 (32B)
# Liveness tomb_bits:       8B
# Liveness Extra Data:      0 (0B)
# Liveness special table:   0 (0B)
  %0 = arg(u8)
  %1 = ret_ptr(*repro.unionInit__union_175)
  %2 = struct_field_ptr_index_0(*u8, %1)
  %3!= store_safe(%2!, %0!)
  %4!= set_union_tag(%1, <@typeInfo(repro.unionInit__union_175).@"union".tag_type.?, .val>)
  %5!= ret_load(%1!)
# End Function AIR: repro.unionInit

# Begin Function AIR: repro.unionAccess:
# Total AIR+Liveness bytes: 167B
# AIR Instructions:         3 (27B)
# AIR Extra Data:           7 (28B)
# Liveness tomb_bits:       8B
# Liveness Extra Data:      0 (0B)
# Liveness special table:   0 (0B)
  %0 = arg(repro.unionAccess__union_181)
  %1 = struct_field_val(%0!, 0)
  %2!= ret_safe(%1!)
# End Function AIR: repro.unionAccess