bjoernager/rust
bjoernager/rust
1
Fork 0
Code Activity

Use br instead of conditional when branching on constant

Browse source
This commit is contained in:
clubby789 2024-02-05 16:15:47 +00:00
parent 397937d812
commit 7159aed51e
2 changed files with 80 additions and 5 deletions
Download patch file Download diff file Expand all files Collapse all files

18
compiler/rustc_codegen_ssa/src/mir/block.rs
View file

@ -319,7 +319,15 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
targets: &SwitchTargets,
) {
let discr = self.codegen_operand(bx, discr);
let discr_value = discr.immediate();
let switch_ty = discr.layout.ty;
// If our discriminant is a constant we can branch directly
if let Some(const_discr) = bx.const_to_opt_u128(discr_value, false) {
let target = targets.target_for_value(const_discr);
bx.br(helper.llbb_with_cleanup(self, target));
return;
};
let mut target_iter = targets.iter();
if target_iter.len() == 1 {
// If there are two targets (one conditional, one fallback), emit `br` instead of
@ -330,14 +338,14 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
if switch_ty == bx.tcx().types.bool {
// Don't generate trivial icmps when switching on bool.
match test_value {
0 => bx.cond_br(discr.immediate(), llfalse, lltrue),
1 => bx.cond_br(discr.immediate(), lltrue, llfalse),
0 => bx.cond_br(discr_value, llfalse, lltrue),
1 => bx.cond_br(discr_value, lltrue, llfalse),
_ => bug!(),
}
} else {
let switch_llty = bx.immediate_backend_type(bx.layout_of(switch_ty));
let llval = bx.const_uint_big(switch_llty, test_value);
let cmp = bx.icmp(IntPredicate::IntEQ, discr.immediate(), llval);
let cmp = bx.icmp(IntPredicate::IntEQ, discr_value, llval);
bx.cond_br(cmp, lltrue, llfalse);
}
} else if self.cx.sess().opts.optimize == OptLevel::No
@ -362,11 +370,11 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
let ll2 = helper.llbb_with_cleanup(self, target2);
let switch_llty = bx.immediate_backend_type(bx.layout_of(switch_ty));
let llval = bx.const_uint_big(switch_llty, test_value1);
let cmp = bx.icmp(IntPredicate::IntEQ, discr.immediate(), llval);
let cmp = bx.icmp(IntPredicate::IntEQ, discr_value, llval);
bx.cond_br(cmp, ll1, ll2);
} else {
bx.switch(
discr.immediate(),
discr_value,
helper.llbb_with_cleanup(self, targets.otherwise()),
target_iter.map(|(value, target)| (value, helper.llbb_with_cleanup(self, target))),
);