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Rollup merge of #51323 - nikic:switch-int-lowering, r=nagisa 

Generate br for all two target SwitchInts

Instead of only for booleans. This means that `if let` also becomes a br.

Apart from making the IR slightly simpler, this is supported by FastISel (#4353).
This commit is contained in:
Mark Simulacrum 2018-06-03 18:18:05 -06:00 committed by GitHub
parent 79dd148458 4f4f7dfc00
commit e7ae1b2648
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GPG Key ID: 4AEE18F83AFDEB23
1 changed files with 14 additions and 5 deletions
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19
src/librustc_codegen_llvm/mir/block.rs
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@ -191,14 +191,23 @@ impl<'a, 'tcx> FunctionCx<'a, 'tcx> {
mir::TerminatorKind::SwitchInt { ref discr, switch_ty, ref values, ref targets } => {
let discr = self.codegen_operand(&bx, discr);
if switch_ty == bx.tcx().types.bool {
if targets.len() == 2 {
// If there are two targets, emit br instead of switch
let lltrue = llblock(self, targets[0]);
let llfalse = llblock(self, targets[1]);
if let [0] = values[..] {
bx.cond_br(discr.immediate(), llfalse, lltrue);
if switch_ty == bx.tcx().types.bool {
// Don't generate trivial icmps when switching on bool
if let [0] = values[..] {
bx.cond_br(discr.immediate(), llfalse, lltrue);
} else {
assert_eq!(&values[..], &[1]);
bx.cond_br(discr.immediate(), lltrue, llfalse);
}
} else {
assert_eq!(&values[..], &[1]);
bx.cond_br(discr.immediate(), lltrue, llfalse);
let switch_llty = bx.cx.layout_of(switch_ty).immediate_llvm_type(bx.cx);
let llval = C_uint_big(switch_llty, values[0]);
let cmp = bx.icmp(llvm::IntEQ, discr.immediate(), llval);
bx.cond_br(cmp, lltrue, llfalse);
}
} else {
let (otherwise, targets) = targets.split_last().unwrap();