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Use LLVM intrinsics for saturating add/sub

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This commit is contained in:
Nikita Popov 2019-01-29 22:16:43 +01:00
parent d8a0dd7ae8
commit 4a4186e4d1
5 changed files with 101 additions and 3 deletions
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24
src/librustc_codegen_llvm/context.rs
View file

@ -757,6 +757,30 @@ impl CodegenCx<'b, 'tcx> {
ifn!("llvm.umul.with.overflow.i64", fn(t_i64, t_i64) -> mk_struct!{t_i64, i1});
ifn!("llvm.umul.with.overflow.i128", fn(t_i128, t_i128) -> mk_struct!{t_i128, i1});
ifn!("llvm.sadd.sat.i8", fn(t_i8, t_i8) -> t_i8);
ifn!("llvm.sadd.sat.i16", fn(t_i16, t_i16) -> t_i16);
ifn!("llvm.sadd.sat.i32", fn(t_i32, t_i32) -> t_i32);
ifn!("llvm.sadd.sat.i64", fn(t_i64, t_i64) -> t_i64);
ifn!("llvm.sadd.sat.i128", fn(t_i128, t_i128) -> t_i128);
ifn!("llvm.uadd.sat.i8", fn(t_i8, t_i8) -> t_i8);
ifn!("llvm.uadd.sat.i16", fn(t_i16, t_i16) -> t_i16);
ifn!("llvm.uadd.sat.i32", fn(t_i32, t_i32) -> t_i32);
ifn!("llvm.uadd.sat.i64", fn(t_i64, t_i64) -> t_i64);
ifn!("llvm.uadd.sat.i128", fn(t_i128, t_i128) -> t_i128);
ifn!("llvm.ssub.sat.i8", fn(t_i8, t_i8) -> t_i8);
ifn!("llvm.ssub.sat.i16", fn(t_i16, t_i16) -> t_i16);
ifn!("llvm.ssub.sat.i32", fn(t_i32, t_i32) -> t_i32);
ifn!("llvm.ssub.sat.i64", fn(t_i64, t_i64) -> t_i64);
ifn!("llvm.ssub.sat.i128", fn(t_i128, t_i128) -> t_i128);
ifn!("llvm.usub.sat.i8", fn(t_i8, t_i8) -> t_i8);
ifn!("llvm.usub.sat.i16", fn(t_i16, t_i16) -> t_i16);
ifn!("llvm.usub.sat.i32", fn(t_i32, t_i32) -> t_i32);
ifn!("llvm.usub.sat.i64", fn(t_i64, t_i64) -> t_i64);
ifn!("llvm.usub.sat.i128", fn(t_i128, t_i128) -> t_i128);
ifn!("llvm.lifetime.start", fn(t_i64,i8p) -> void);
ifn!("llvm.lifetime.end", fn(t_i64, i8p) -> void);

44
src/librustc_codegen_llvm/intrinsic.rs
View file

@ -14,7 +14,7 @@ use type_::Type;
use type_of::LayoutLlvmExt;
use rustc::ty::{self, Ty};
use rustc::ty::layout::{self, LayoutOf, HasTyCtxt, Primitive};
use rustc_codegen_ssa::common::TypeKind;
use rustc_codegen_ssa::common::{IntPredicate, TypeKind};
use rustc::hir;
use syntax::ast::{self, FloatTy};
use syntax::symbol::Symbol;
@ -28,7 +28,7 @@ use rustc::session::Session;
use syntax_pos::Span;
use std::cmp::Ordering;
use std::iter;
use std::{iter, i128, u128};
fn get_simple_intrinsic(cx: &CodegenCx<'ll, '_>, name: &str) -> Option<&'ll Value> {
let llvm_name = match name {
@ -342,7 +342,7 @@ impl IntrinsicCallMethods<'tcx> for Builder<'a, 'll, 'tcx> {
"bitreverse" | "add_with_overflow" | "sub_with_overflow" |
"mul_with_overflow" | "overflowing_add" | "overflowing_sub" | "overflowing_mul" |
"unchecked_div" | "unchecked_rem" | "unchecked_shl" | "unchecked_shr" | "exact_div" |
"rotate_left" | "rotate_right" => {
"rotate_left" | "rotate_right" | "saturating_add" | "saturating_sub" => {
let ty = arg_tys[0];
match int_type_width_signed(ty, self) {
Some((width, signed)) =>
@ -468,6 +468,44 @@ impl IntrinsicCallMethods<'tcx> for Builder<'a, 'll, 'tcx> {
self.or(shift1, shift2)
}
},
"saturating_add" | "saturating_sub" => {
let is_add = name == "saturating_add";
let lhs = args[0].immediate();
let rhs = args[1].immediate();
if llvm_util::get_major_version() >= 8 {
let llvm_name = &format!("llvm.{}{}.sat.i{}",
if signed { 's' } else { 'u' },
if is_add { "add" } else { "sub" },
width);
let llfn = self.get_intrinsic(llvm_name);
self.call(llfn, &[lhs, rhs], None)
} else {
let llvm_name = &format!("llvm.{}{}.with.overflow.i{}",
if signed { 's' } else { 'u' },
if is_add { "add" } else { "sub" },
width);
let llfn = self.get_intrinsic(llvm_name);
let pair = self.call(llfn, &[lhs, rhs], None);
let val = self.extract_value(pair, 0);
let overflow = self.extract_value(pair, 1);
let llty = self.type_ix(width);
let limit = if signed {
let limit_lo = self.const_uint_big(
llty, (i128::MIN >> (128 - width)) as u128);
let limit_hi = self.const_uint_big(
llty, (i128::MAX >> (128 - width)) as u128);
let neg = self.icmp(
IntPredicate::IntSLT, val, self.const_uint(llty, 0));
self.select(neg, limit_hi, limit_lo)
} else if is_add {
self.const_uint_big(llty, u128::MAX >> (128 - width))
} else {
self.const_uint(llty, 0)
};
self.select(overflow, limit, val)
}
},
_ => bug!(),
},
None => {