Use trunc nuw+br for 0/1 branches even in optimized builds
Rather than needing to use `switch` for them to include the `unreachable` arm
This commit is contained in:
Scott McMurray
parent
30f168ef81
commit
d9432acfe1
6 changed files with 118 additions and 8 deletions
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@ -3,6 +3,7 @@ use std::cmp;
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use rustc_abi::{BackendRepr, ExternAbi, HasDataLayout, Reg, WrappingRange};
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use rustc_ast as ast;
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use rustc_ast::{InlineAsmOptions, InlineAsmTemplatePiece};
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use rustc_data_structures::packed::Pu128;
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use rustc_hir::lang_items::LangItem;
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use rustc_middle::mir::{self, AssertKind, InlineAsmMacro, SwitchTargets, UnwindTerminateReason};
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use rustc_middle::ty::layout::{HasTyCtxt, LayoutOf, ValidityRequirement};
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@ -406,6 +407,39 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
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let cmp = bx.icmp(IntPredicate::IntEQ, discr_value, llval);
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bx.cond_br_with_expect(cmp, lltarget, llotherwise, expect);
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}
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} else if target_iter.len() == 2
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&& self.mir[targets.otherwise()].is_empty_unreachable()
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&& targets.all_values().contains(&Pu128(0))
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&& targets.all_values().contains(&Pu128(1))
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{
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// This is the really common case for `bool`, `Option`, etc.
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// By using `trunc nuw` we communicate that other values are
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// impossible without needing `switch` or `assume`s.
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let true_bb = targets.target_for_value(1);
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let false_bb = targets.target_for_value(0);
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let true_ll = helper.llbb_with_cleanup(self, true_bb);
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let false_ll = helper.llbb_with_cleanup(self, false_bb);
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let expected_cond_value = if self.cx.sess().opts.optimize == OptLevel::No {
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None
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} else {
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match (self.cold_blocks[true_bb], self.cold_blocks[false_bb]) {
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// Same coldness, no expectation
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(true, true) | (false, false) => None,
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// Different coldness, expect the non-cold one
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(true, false) => Some(false),
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(false, true) => Some(true),
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}
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};
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let bool_ty = bx.tcx().types.bool;
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let cond = if switch_ty == bool_ty {
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discr_value
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} else {
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let bool_llty = bx.immediate_backend_type(bx.layout_of(bool_ty));
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bx.unchecked_utrunc(discr_value, bool_llty)
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};
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bx.cond_br_with_expect(cond, true_ll, false_ll, expected_cond_value);
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} else if self.cx.sess().opts.optimize == OptLevel::No
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&& target_iter.len() == 2
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&& self.mir[targets.otherwise()].is_empty_unreachable()
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51
tests/codegen/enum/enum-two-variants-match.rs
Normal file
51
tests/codegen/enum/enum-two-variants-match.rs
Normal file
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@ -0,0 +1,51 @@
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//@ compile-flags: -Copt-level=3 -C no-prepopulate-passes
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//@ min-llvm-version: 19 (for trunc nuw)
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//@ only-x86_64 (because these discriminants are isize)
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#![crate_type = "lib"]
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// CHECK-LABEL: @option_match
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#[no_mangle]
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pub fn option_match(x: Option<i32>) -> u16 {
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// CHECK: %x = alloca [8 x i8]
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// CHECK: store i32 %0, ptr %x
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// CHECK: %[[TAG:.+]] = load i32, ptr %x
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// CHECK-SAME: !range ![[ZERO_ONE_32:[0-9]+]]
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// CHECK: %[[DISCR:.+]] = zext i32 %[[TAG]] to i64
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// CHECK: %[[COND:.+]] = trunc nuw i64 %[[DISCR]] to i1
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// CHECK: br i1 %[[COND]], label %[[TRUE:[a-z0-9]+]], label %[[FALSE:[a-z0-9]+]]
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// CHECK: [[TRUE]]:
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// CHECK: store i16 13
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// CHECK: [[FALSE]]:
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// CHECK: store i16 42
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match x {
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Some(_) => 13,
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None => 42,
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}
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}
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// CHECK-LABEL: @result_match
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#[no_mangle]
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pub fn result_match(x: Result<u64, i64>) -> u16 {
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// CHECK: %x = alloca [16 x i8]
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// CHECK: store i64 %0, ptr %x
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// CHECK: %[[DISCR:.+]] = load i64, ptr %x
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// CHECK-SAME: !range ![[ZERO_ONE_64:[0-9]+]]
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// CHECK: %[[COND:.+]] = trunc nuw i64 %[[DISCR]] to i1
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// CHECK: br i1 %[[COND]], label %[[TRUE:[a-z0-9]+]], label %[[FALSE:[a-z0-9]+]]
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// CHECK: [[TRUE]]:
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// CHECK: store i16 13
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// CHECK: [[FALSE]]:
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// CHECK: store i16 42
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match x {
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Err(_) => 13,
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Ok(_) => 42,
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}
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}
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// CHECK: ![[ZERO_ONE_32]] = !{i32 0, i32 2}
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// CHECK: ![[ZERO_ONE_64]] = !{i64 0, i64 2}
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@ -26,7 +26,8 @@ pub fn test(x: Option<bool>) {
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}
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// CHECK-LABEL: @test(
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// CHECK: br i1 %1, label %bb2, label %bb1, !prof ![[NUM:[0-9]+]]
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// CHECK: %[[IS_NONE:.+]] = icmp eq i8 %0, 2
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// CHECK: br i1 %[[IS_NONE]], label %bb2, label %bb1, !prof ![[NUM:[0-9]+]]
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// CHECK: bb1:
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// CHECK: path_a
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// CHECK: bb2:
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@ -1,5 +1,6 @@
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//@ compile-flags: -Copt-level=3
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//@ revisions: host x86-64-v3
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//@ min-llvm-version: 20
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// This particular CPU regressed in #131563
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//@[x86-64-v3] only-x86_64
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@ -3,6 +3,11 @@
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#![crate_type = "lib"]
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// The bug here was that it was loading and storing the whole value.
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// It's ok for it to load the discriminant,
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// to preserve the UB from `unreachable_unchecked`,
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// but it better only store the constant discriminant of `B`.
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pub enum State {
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A([u8; 753]),
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B([u8; 753]),
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@ -11,9 +16,27 @@ pub enum State {
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// CHECK-LABEL: @update
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#[no_mangle]
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pub unsafe fn update(s: *mut State) {
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// CHECK-NEXT: start:
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// CHECK-NEXT: store i8
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// CHECK-NEXT: ret
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// CHECK-NOT: alloca
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// CHECK-NOT: load
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// CHECK-NOT: store
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// CHECK-NOT: memcpy
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// CHECK-NOT: 75{{3|4}}
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// CHECK: %[[TAG:.+]] = load i8, ptr %s, align 1
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// CHECK-NEXT: trunc nuw i8 %[[TAG]] to i1
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// CHECK-NOT: load
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// CHECK-NOT: store
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// CHECK-NOT: memcpy
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// CHECK-NOT: 75{{3|4}}
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// CHECK: store i8 1, ptr %s, align 1
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// CHECK-NOT: load
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// CHECK-NOT: store
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// CHECK-NOT: memcpy
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// CHECK-NOT: 75{{3|4}}
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let State::A(v) = s.read() else { std::hint::unreachable_unchecked() };
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s.write(State::B(v));
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}
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@ -16,8 +16,8 @@ use std::ptr::NonNull;
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#[no_mangle]
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pub fn option_nop_match_32(x: Option<u32>) -> Option<u32> {
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// CHECK: start:
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// TWENTY-NEXT: %trunc = trunc nuw i32 %0 to i1
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// TWENTY-NEXT: %.2 = select i1 %trunc, i32 %1, i32 undef
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// TWENTY-NEXT: %[[IS_SOME:.+]] = trunc nuw i32 %0 to i1
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// TWENTY-NEXT: %.2 = select i1 %[[IS_SOME]], i32 %1, i32 undef
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// CHECK-NEXT: [[REG1:%.*]] = insertvalue { i32, i32 } poison, i32 %0, 0
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// NINETEEN-NEXT: [[REG2:%.*]] = insertvalue { i32, i32 } [[REG1]], i32 %1, 1
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// TWENTY-NEXT: [[REG2:%.*]] = insertvalue { i32, i32 } [[REG1]], i32 %.2, 1
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@ -32,8 +32,8 @@ pub fn option_nop_match_32(x: Option<u32>) -> Option<u32> {
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#[no_mangle]
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pub fn option_nop_traits_32(x: Option<u32>) -> Option<u32> {
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// CHECK: start:
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// TWENTY-NEXT: %trunc = trunc nuw i32 %0 to i1
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// TWENTY-NEXT: %.1 = select i1 %trunc, i32 %1, i32 undef
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// TWENTY-NEXT: %[[IS_SOME:.+]] = trunc nuw i32 %0 to i1
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// TWENTY-NEXT: %.1 = select i1 %[[IS_SOME]], i32 %1, i32 undef
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// CHECK-NEXT: insertvalue { i32, i32 }
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// CHECK-NEXT: insertvalue { i32, i32 }
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// CHECK-NEXT: ret { i32, i32 }
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