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Allow spilling of EBB arguments.

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When the spiller needs to make a register available for a conditional
branch instruction, it can be necessary to spill some of the EBB
arguments on the branch instruction. This is ok because EBB argument
values belong to the same virtual register as the corresponding EBB
parameter and we spill the whole virtreg to the same slot.

Also make sure free_regs() can handle values that are killed by the
current instruction *and* spilled.
This commit is contained in:
Jakob Stoklund Olesen
2017-12-14 10:57:10 -06:00
parent d617d5e0f3
commit febe8e0e51
2 changed files with 38 additions and 3 deletions
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24
cranelift/filetests/regalloc/spill.cton
View File

@@ -145,6 +145,30 @@ ebb1(v10: i32, v11: i32, v12: i32, v13: i32, v14: i32, v15: i32, v16: i32, v17:
return v33
}
; Spilling an EBB argument to make room for a branch operand.
function %brargs(i32) -> i32 {
ebb0(v1: i32):
; check: $v1 = spill
v2 = iconst.i32 1
brnz v1, ebb1(v2, v2, v2, v2, v2, v2, v2, v2, v2, v2, v2, v2)
return v1
ebb1(v10: i32, v11: i32, v12: i32, v13: i32, v14: i32, v15: i32, v16: i32, v17: i32, v18: i32, v19: i32, v20: i32, v21: i32):
v22 = iadd v10, v11
v23 = iadd v22, v12
v24 = iadd v23, v13
v25 = iadd v24, v14
v26 = iadd v25, v15
v27 = iadd v26, v16
v28 = iadd v27, v17
v29 = iadd v28, v18
v30 = iadd v29, v19
v31 = iadd v30, v20
v32 = iadd v31, v21
v33 = iadd v32, v1
return v33
}
; In straight-line code, the first value defined is spilled.
; That is in order:
; 1. The argument v1.

17
lib/cretonne/src/regalloc/spilling.rs
View File

@@ -155,8 +155,10 @@ impl<'a> Context<'a> {
fn free_regs(&mut self, kills: &[LiveValue]) {
for lv in kills {
if let Affinity::Reg(rci) = lv.affinity {
let rc = self.reginfo.rc(rci);
self.pressure.free(rc);
if !self.spills.contains(&lv.value) {
let rc = self.reginfo.rc(rci);
self.pressure.free(rc);
}
}
}
}
@@ -402,8 +404,17 @@ impl<'a> Context<'a> {
dbg!("Copy of {} reg causes spill", rc);
// Spill a live register that is *not* used by the current instruction.
// Spilling a use wouldn't help.
//
// Do allow spilling of EBB arguments on branches. This is safe since we spill
// the whole virtual register which includes the matching EBB parameter value
// at the branch destination. It is also necessary since there can be
// arbitrarily many EBB arguments.
match {
let args = self.cur.func.dfg.inst_args(inst);
let args = if self.cur.func.dfg[inst].opcode().is_branch() {
self.cur.func.dfg.inst_fixed_args(inst)
} else {
self.cur.func.dfg.inst_args(inst)
};
self.spill_candidate(
mask,
tracker.live().iter().filter(|lv| !args.contains(&lv.value)),