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C backend: avoid branching multiple times on AIR tag

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for cmp_eq and cmp_neq.
This commit is contained in:
Andrew Kelley 2021-11-23 13:54:08 -07:00
parent 2e15a404e2
commit 7ee02b5e70
1 changed files with 12 additions and 8 deletions
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20
src/codegen/c.zig
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@ -1162,12 +1162,13 @@ fn genBody(f: *Function, body: []const Air.Inst.Index) error{ AnalysisFail, OutO
.slice => try airSlice(f, inst),
.cmp_eq => try airEquality(f, inst, .cmp_eq),
.cmp_gt => try airBinOp(f, inst, " > "),
.cmp_gte => try airBinOp(f, inst, " >= "),
.cmp_lt => try airBinOp(f, inst, " < "),
.cmp_lte => try airBinOp(f, inst, " <= "),
.cmp_neq => try airEquality(f, inst, .cmp_neq),
.cmp_eq => try airEquality(f, inst, "((", "=="),
.cmp_neq => try airEquality(f, inst, "!((", "!="),
// bool_and and bool_or are non-short-circuit operations
.bool_and => try airBinOp(f, inst, " & "),
@ -1908,9 +1909,13 @@ fn airBinOp(f: *Function, inst: Air.Inst.Index, operator: [*:0]const u8) !CValue
return local;
}
fn airEquality(f: *Function, inst: Air.Inst.Index, op: Air.Inst.Tag) !CValue {
if (f.liveness.isUnused(inst))
return CValue.none;
fn airEquality(
f: *Function,
inst: Air.Inst.Index,
negate_prefix: []const u8,
eq_op_str: []const u8,
) !CValue {
if (f.liveness.isUnused(inst)) return CValue.none;
const bin_op = f.air.instructions.items(.data)[inst].bin_op;
const lhs = try f.resolveInst(bin_op.lhs);
@ -1927,7 +1932,7 @@ fn airEquality(f: *Function, inst: Air.Inst.Index, op: Air.Inst.Tag) !CValue {
// (A && B) || (C && (A == B))
// A = lhs.is_null ; B = rhs.is_null ; C = rhs.payload == lhs.payload
try writer.writeAll(if (op == .cmp_eq) "((" else "!((");
try writer.writeAll(negate_prefix);
try f.writeCValue(writer, lhs);
try writer.writeAll(".is_null && ");
try f.writeCValue(writer, rhs);
@ -1944,9 +1949,8 @@ fn airEquality(f: *Function, inst: Air.Inst.Index, op: Air.Inst.Tag) !CValue {
return local;
}
const operator = if (op == .cmp_eq) "==" else "!=";
try f.writeCValue(writer, lhs);
try writer.print("{s}", .{operator});
try writer.writeAll(eq_op_str);
try f.writeCValue(writer, rhs);
try writer.writeAll(";\n");