From 2ff5a3e38b59dc8dc443c7459d2825130ffed4bc Mon Sep 17 00:00:00 2001 From: Erik Desjardins Date: Sun, 5 Dec 2021 15:55:50 -0500 Subject: Attach range metadata to alignment loads from vtables ...because alignment is always nonzero. This helps eliminate redundant runtime alignment checks, when a DST is a field of a struct whose remaining fields have alignment 1. --- compiler/rustc_codegen_ssa/src/glue.rs | 18 +++++++++++------- 1 file changed, 11 insertions(+), 7 deletions(-) (limited to 'compiler/rustc_codegen_ssa/src') diff --git a/compiler/rustc_codegen_ssa/src/glue.rs b/compiler/rustc_codegen_ssa/src/glue.rs index cf217b52c86..2c4e6bbe9a5 100644 --- a/compiler/rustc_codegen_ssa/src/glue.rs +++ b/compiler/rustc_codegen_ssa/src/glue.rs @@ -6,6 +6,7 @@ use crate::common::IntPredicate; use crate::meth; use crate::traits::*; use rustc_middle::ty::{self, Ty}; +use rustc_target::abi::WrappingRange; pub fn size_and_align_of_dst<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>( bx: &mut Bx, @@ -21,14 +22,17 @@ pub fn size_and_align_of_dst<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>( } match t.kind() { ty::Dynamic(..) => { - // load size/align from vtable + // Load size/align from vtable. let vtable = info.unwrap(); - ( - meth::VirtualIndex::from_index(ty::COMMON_VTABLE_ENTRIES_SIZE) - .get_usize(bx, vtable), - meth::VirtualIndex::from_index(ty::COMMON_VTABLE_ENTRIES_ALIGN) - .get_usize(bx, vtable), - ) + let size = meth::VirtualIndex::from_index(ty::COMMON_VTABLE_ENTRIES_SIZE) + .get_usize(bx, vtable); + let align = meth::VirtualIndex::from_index(ty::COMMON_VTABLE_ENTRIES_ALIGN) + .get_usize(bx, vtable); + + // Alignment is always nonzero. + bx.range_metadata(align, WrappingRange { start: 1, end: !0 }); + + (size, align) } ty::Slice(_) | ty::Str => { let unit = layout.field(bx, 0); -- cgit 1.4.1-3-g733a5