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aarch64: fix reg/imm sub insts that read SP, not the zero register.

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On AArch64, the zero register (xzr) and the stack pointer (xsp) are
alternately named by the same index `31` in machine code depending on
context. In particular, in the reg-reg-immediate ALU instruction form,
add/subtract will use the stack pointer, not the zero register, if index
31 is given for the first (register) source arg.

In a few places, we were emitting subtract instructions with the zero
register as an argument and a reg/immediate as the second argument. When
an immediate could be incorporated directly (we have the `iconst`
definition visible), this would result in incorrect code being
generated.

This issue was found in `ineg` and in the sequence for vector
right-shifts.

Reported by Ian Cullinan; thanks!
This commit is contained in:
Chris Fallin
2021-01-05 15:48:07 -08:00
parent 2b325a1878
commit aac3751025
2 changed files with 41 additions and 4 deletions
Download Patch File Download Diff File Expand all files Collapse all files

13
cranelift/codegen/src/isa/aarch64/lower_inst.rs
View File

@@ -215,9 +215,9 @@ pub(crate) fn lower_insn_to_regs<C: LowerCtx<I = Inst>>(
let ty = ty.unwrap();
if !ty.is_vector() {
let rn = zero_reg();
let rm = put_input_in_rse_imm12(ctx, inputs[0], NarrowValueMode::None);
let rm = put_input_in_reg(ctx, inputs[0], NarrowValueMode::None);
let alu_op = choose_32_64(ty, ALUOp::Sub32, ALUOp::Sub64);
ctx.emit(alu_inst_imm12(alu_op, rd, rn, rm));
ctx.emit(Inst::AluRRR { alu_op, rd, rn, rm });
} else {
let rn = put_input_in_reg(ctx, inputs[0], NarrowValueMode::None);
ctx.emit(Inst::VecMisc {
@@ -693,9 +693,14 @@ pub(crate) fn lower_insn_to_regs<C: LowerCtx<I = Inst>>(
let rm = if is_right_shift {
// Right shifts are implemented with a negative left shift.
let tmp = ctx.alloc_tmp(RegClass::I64, I32);
let rm = put_input_in_rse_imm12(ctx, inputs[1], NarrowValueMode::None);
let rm = put_input_in_reg(ctx, inputs[1], NarrowValueMode::None);
let rn = zero_reg();
ctx.emit(alu_inst_imm12(ALUOp::Sub32, tmp, rn, rm));
ctx.emit(Inst::AluRRR {
alu_op: ALUOp::Sub32,
rd: tmp,
rn,
rm,
});
tmp.to_reg()
} else {
put_input_in_reg(ctx, inputs[1], NarrowValueMode::None)