Generate MIR thats easier for llvm for str matches
LLVM appears to prefer (spend less time optimizing) long if chains if it receives them in approzimately source order. This fixes a ~10% regression for optimized builds of the encoding benchmark on perf.rlo due to the changes to decision tree construction.
This commit is contained in:
Matthew Jasper
parent
ef1fc86b52
commit
a1d0266878
@ -1198,51 +1198,58 @@ fn test_candidates<'pat, 'b, 'c>(
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debug!("tested_candidates: {}", total_candidate_count - candidates.len());
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debug!("untested_candidates: {}", candidates.len());
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// For each outcome of test, process the candidates that still
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// apply. Collect a list of blocks where control flow will
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// branch if one of the `target_candidate` sets is not
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// exhaustive.
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if !candidates.is_empty() {
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let remainder_start = &mut None;
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self.match_candidates(
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span,
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remainder_start,
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otherwise_block,
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candidates,
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fake_borrows,
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);
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otherwise_block = Some(remainder_start.unwrap());
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};
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let target_blocks: Vec<_> = target_candidates.into_iter().map(|mut candidates| {
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if candidates.len() != 0 {
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let candidate_start = &mut None;
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self.match_candidates(
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// HACK(matthewjasper) This is a closure so that we can let the test
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// create its blocks before the rest of the match. This currently
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// improves the speed of llvm when optimizing long string literal
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// matches
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let make_target_blocks = move |this: &mut Self| -> Vec<BasicBlock> {
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// For each outcome of test, process the candidates that still
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// apply. Collect a list of blocks where control flow will
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// branch if one of the `target_candidate` sets is not
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// exhaustive.
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if !candidates.is_empty() {
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let remainder_start = &mut None;
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this.match_candidates(
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span,
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candidate_start,
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remainder_start,
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otherwise_block,
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&mut *candidates,
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candidates,
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fake_borrows,
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);
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candidate_start.unwrap()
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} else {
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*otherwise_block.get_or_insert_with(|| {
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let unreachable = self.cfg.start_new_block();
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let source_info = self.source_info(span);
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self.cfg.terminate(
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unreachable,
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source_info,
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TerminatorKind::Unreachable,
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otherwise_block = Some(remainder_start.unwrap());
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};
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target_candidates.into_iter().map(|mut candidates| {
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if candidates.len() != 0 {
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let candidate_start = &mut None;
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this.match_candidates(
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span,
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candidate_start,
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otherwise_block,
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&mut *candidates,
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fake_borrows,
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);
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unreachable
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})
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}
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}).collect();
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candidate_start.unwrap()
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} else {
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*otherwise_block.get_or_insert_with(|| {
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let unreachable = this.cfg.start_new_block();
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let source_info = this.source_info(span);
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this.cfg.terminate(
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unreachable,
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source_info,
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TerminatorKind::Unreachable,
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);
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unreachable
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})
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}
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}).collect()
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};
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self.perform_test(
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block,
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&match_place,
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&test,
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target_blocks,
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make_target_blocks,
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);
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}
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@ -168,7 +168,7 @@ pub fn perform_test(
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block: BasicBlock,
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place: &Place<'tcx>,
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test: &Test<'tcx>,
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target_blocks: Vec<BasicBlock>,
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make_target_blocks: impl FnOnce(&mut Self) -> Vec<BasicBlock>,
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) {
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debug!("perform_test({:?}, {:?}: {:?}, {:?})",
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block,
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@ -179,6 +179,7 @@ pub fn perform_test(
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let source_info = self.source_info(test.span);
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match test.kind {
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TestKind::Switch { adt_def, ref variants } => {
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let target_blocks = make_target_blocks(self);
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// Variants is a BitVec of indexes into adt_def.variants.
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let num_enum_variants = adt_def.variants.len();
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let used_variants = variants.count();
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@ -223,6 +224,7 @@ pub fn perform_test(
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}
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TestKind::SwitchInt { switch_ty, ref options, indices: _ } => {
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let target_blocks = make_target_blocks(self);
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let terminator = if switch_ty.sty == ty::Bool {
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assert!(options.len() > 0 && options.len() <= 2);
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if let [first_bb, second_bb] = *target_blocks {
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@ -254,38 +256,38 @@ pub fn perform_test(
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}
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TestKind::Eq { value, ty } => {
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if let [success, fail] = *target_blocks {
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if !ty.is_scalar() {
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// Use `PartialEq::eq` instead of `BinOp::Eq`
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// (the binop can only handle primitives)
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self.non_scalar_compare(
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block,
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success,
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fail,
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source_info,
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value,
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place,
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ty,
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);
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} else {
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if !ty.is_scalar() {
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// Use `PartialEq::eq` instead of `BinOp::Eq`
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// (the binop can only handle primitives)
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self.non_scalar_compare(
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block,
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make_target_blocks,
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source_info,
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value,
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place,
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ty,
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);
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} else {
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if let [success, fail] = *make_target_blocks(self) {
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let val = Operand::Copy(place.clone());
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let expect = self.literal_operand(test.span, ty, value);
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self.compare(block, success, fail, source_info, BinOp::Eq, expect, val);
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} else {
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bug!("`TestKind::Eq` should have two target blocks");
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}
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} else {
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bug!("`TestKind::Eq` should have two target blocks")
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};
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}
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}
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TestKind::Range(PatternRange { ref lo, ref hi, ty, ref end }) => {
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let lower_bound_success = self.cfg.start_new_block();
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let target_blocks = make_target_blocks(self);
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// Test `val` by computing `lo <= val && val <= hi`, using primitive comparisons.
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let lo = self.literal_operand(test.span, ty, lo);
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let hi = self.literal_operand(test.span, ty, hi);
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let val = Operand::Copy(place.clone());
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if let [success, fail] = *target_blocks {
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let lower_bound_success = self.cfg.start_new_block();
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self.compare(
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block,
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lower_bound_success,
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@ -306,6 +308,8 @@ pub fn perform_test(
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}
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TestKind::Len { len, op } => {
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let target_blocks = make_target_blocks(self);
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let usize_ty = self.hir.usize_ty();
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let actual = self.temp(usize_ty, test.span);
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@ -374,8 +378,7 @@ fn compare(
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fn non_scalar_compare(
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&mut self,
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block: BasicBlock,
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success_block: BasicBlock,
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fail_block: BasicBlock,
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make_target_blocks: impl FnOnce(&mut Self) -> Vec<BasicBlock>,
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source_info: SourceInfo,
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value: &'tcx ty::Const<'tcx>,
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place: &Place<'tcx>,
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@ -461,17 +464,21 @@ fn non_scalar_compare(
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from_hir_call: false,
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});
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// check the result
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self.cfg.terminate(
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eq_block,
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source_info,
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TerminatorKind::if_(
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self.hir.tcx(),
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Operand::Move(eq_result),
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success_block,
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fail_block,
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),
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);
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if let [success_block, fail_block] = *make_target_blocks(self) {
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// check the result
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self.cfg.terminate(
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eq_block,
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source_info,
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TerminatorKind::if_(
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self.hir.tcx(),
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Operand::Move(eq_result),
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success_block,
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fail_block,
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),
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);
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} else {
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bug!("`TestKind::Eq` should have two target blocks")
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}
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}
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/// Given that we are performing `test` against `test_place`, this job
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