From 17c023383b8fbb2c2d2ad17e1d0f74c1eb27ff7a Mon Sep 17 00:00:00 2001
From: Forest Belton <forest@homolo.gy>
Date: Wed, 15 Sep 2021 14:26:43 -0400
Subject: [PATCH] Build interference graph

---
 lib/data/graph.ts                       |  6 +++
 lib/regalloc.ts                         | 63 +++++++++++++++++++++++++
 test/{live.spec.ts => regalloc.spec.ts} | 18 ++++++-
 3 files changed, 86 insertions(+), 1 deletion(-)
 create mode 100644 lib/regalloc.ts
 rename test/{live.spec.ts => regalloc.spec.ts} (65%)

diff --git a/lib/data/graph.ts b/lib/data/graph.ts
index 804d1a8..ada175a 100644
--- a/lib/data/graph.ts
+++ b/lib/data/graph.ts
@@ -18,6 +18,10 @@ export const createGraph = <V>(cons: (v: AddVertex<V>, e: AddEdge) => void): Gra
     const g: Graph<V> = { numVertices: 0, numEdges: 0, vertices: {}, edges: {} }
 
     const addVertex = (name: string, v: V) => {
+        if (typeof g.vertices[name] !== "undefined") {
+            return
+        }
+
         g.vertices[name] = v
         g.edges[name] = new Set()
         g.numVertices++
@@ -50,6 +54,8 @@ export const neighbors = <V>(g: Graph<V>, name: string): Set<string> => {
 
 export const vertices = <V>(g: Graph<V>): Set<string> => new Set(Object.keys(g.vertices))
 
+export const edgeConnects = <V>(g: Graph<V>, v1: string, v2: string): boolean => g.edges[v1].has(v2)
+
 export const maxCardinalitySearch = <V>(g: Graph<V>): Array<string> => {
     const weights: { [s: string]: number } = {}
     const ordering: Array<string> = []
diff --git a/lib/regalloc.ts b/lib/regalloc.ts
new file mode 100644
index 0000000..c108df3
--- /dev/null
+++ b/lib/regalloc.ts
@@ -0,0 +1,63 @@
+import { createGraph, Graph } from "./data/graph"
+
+import type { Loc } from "./ir/loc"
+import type { SSA } from "./ir/ssa"
+
+export type LivenessInfo = Array<Set<Loc>>
+
+export const liveness = (block: Array<SSA>): LivenessInfo => {
+    const info: LivenessInfo = []
+
+    info[block.length] = new Set()
+    for (let i = block.length - 1; i >= 0; --i) {
+        const insn = block[i]
+        const last = info[i + 1]
+
+        info[i] = new Set()
+
+        if (typeof insn.source !== "number") {
+            info[i].add(insn.source)
+        }
+
+        if ("source1" in insn && typeof insn.source1 !== "number") {
+            info[i].add(insn.source1)
+        }
+
+        last.forEach(loc => {
+            if (loc.toString() === insn.dest.toString()) {
+                return
+            }
+
+            info[i].add(loc)
+        })
+    }
+
+    return info
+}
+
+export const locations = (block: Array<SSA>): Set<Loc> => {
+    const ls: Set<Loc> = new Set()
+
+    block.forEach(ssa => {
+        if ("source1" in ssa && typeof ssa.source1 !== "number") {
+            ls.add(ssa.source1)
+        } else if (typeof ssa.source !== "number") {
+            ls.add(ssa.source)
+        }
+    })
+
+    return ls
+}
+
+export const interference = (block: Array<SSA>, live: LivenessInfo): Graph<Loc> =>
+    createGraph((v, e) => {
+        block.forEach((ssa, i) =>
+            live[i + 1].forEach(u => {
+                if (ssa.dest.toString() !== u.toString()) {
+                    v(ssa.dest.toString(), ssa.dest)
+                    v(u.toString(), u)
+                    e(ssa.dest.toString(), u.toString())
+                }
+            })
+        )
+    })
diff --git a/test/live.spec.ts b/test/regalloc.spec.ts
similarity index 65%
rename from test/live.spec.ts
rename to test/regalloc.spec.ts
index f998cdc..8e684f1 100644
--- a/test/live.spec.ts
+++ b/test/regalloc.spec.ts
@@ -1,8 +1,9 @@
 import { expect } from "chai"
+import { edgeConnects } from "../lib/data/graph"
 
 import { Loc } from "../lib/ir/loc"
 import type { SSA } from "../lib/ir/ssa"
-import { liveness } from "../lib/live"
+import { interference, liveness } from "../lib/regalloc"
 
 describe("liveness", () => {
     it("computes liveness", () => {
@@ -26,3 +27,18 @@ describe("liveness", () => {
         expect(info[4]).to.deep.equal(new Set([y[0], x[2]]))
     })
 })
+
+describe("interference", () => {
+    it("computes interference", () => {
+        const block: Array<SSA> = [
+            { dest: Loc.vari("a"), source: 7 },
+            { dest: Loc.vari("b"), source: 3 },
+            { dest: Loc.vari("x"), source: Loc.vari("a") }
+        ]
+
+        const info = liveness(block)
+        const g = interference(block, info)
+
+        expect(edgeConnects(g, "a", "b")).to.be.true
+    })
+})