From f1395dcd90bcdb27f8d796cf34ac9abba36d98c2 Mon Sep 17 00:00:00 2001
From: "Ben L. Titzer" <ben.titzer@gmail.com>
Date: Mon, 23 Sep 2024 12:39:58 -0400
Subject: [PATCH] [opt] Improve load elimination and SsaOptimizer (#276)

---
 aeneas/src/ir/SsaNormalizer.v3     |  6 ++++++
 aeneas/src/main/Version.v3         |  2 +-
 aeneas/src/ssa/SsaOptimizer.v3     | 28 ++++++++++++++++++++++------
 aeneas/test/SsaInstrReducerTest.v3 |  1 +
 test/core/opt_load12.v3            | 10 ++++++++++
 5 files changed, 40 insertions(+), 7 deletions(-)
 create mode 100644 test/core/opt_load12.v3

diff --git a/aeneas/src/ir/SsaNormalizer.v3 b/aeneas/src/ir/SsaNormalizer.v3
index fd92991f5..95f6e2ff7 100644
--- a/aeneas/src/ir/SsaNormalizer.v3
+++ b/aeneas/src/ir/SsaNormalizer.v3
@@ -28,6 +28,12 @@ class SsaRaNormalizer extends SsaRebuilder {
 			var opt = SsaOptimizer.new(context);
 			opt.optGraph();
 			context.printSsa("Norm Optimized");
+			if (context.compiler.LoadOptimize) {
+				// Perform load elimination.
+				if (SsaLoadOptimizer.new(context).optimize()) {
+					context.printSsa("Load Optimized");
+				}
+			}
 //TODO			SsaGraphVerifier.new(context).verify();
 		}
 	}
diff --git a/aeneas/src/main/Version.v3 b/aeneas/src/main/Version.v3
index 59cc613a8..c1379f9de 100644
--- a/aeneas/src/main/Version.v3
+++ b/aeneas/src/main/Version.v3
@@ -3,6 +3,6 @@
 
 // Updated by VCS scripts. DO NOT EDIT.
 component Version {
-	def version: string = "III-7.1760";
+	def version: string = "III-7.1761";
 	var buildData: string;
 }
diff --git a/aeneas/src/ssa/SsaOptimizer.v3 b/aeneas/src/ssa/SsaOptimizer.v3
index 66e546a44..55a3b0188 100644
--- a/aeneas/src/ssa/SsaOptimizer.v3
+++ b/aeneas/src/ssa/SsaOptimizer.v3
@@ -280,6 +280,7 @@ class SsaInstrReducer(context: SsaContext) extends SsaInstrMatcher {
 	var optimize_nullchecks = true;		// activates null check elimination
 	var optimize_inits = false;		// activates init elimination
 	var optimize_bounds = true;
+	var remove_pure_ops = true;
 	var graph: SsaGraph;
 	var prev: SsaLink;  			// instruction before the current instruction
 	var next: SsaLink;			// instruction after the current instruction
@@ -375,6 +376,7 @@ class SsaInstrReducer(context: SsaContext) extends SsaInstrMatcher {
 		def PURE_LOAD = Fact.O_NO_NULL_CHECK | Fact.O_PURE;
 		def ZERO_NON_ZERO = Fact.V_ZERO | Fact.V_NON_ZERO;
 		def ABOVE_BELOW_ZERO = Fact.V_NON_ZERO | Fact.V_NON_NEGATIVE | Fact.V_BELOW_ZERO;
+		if (remove_pure_ops && i.facts.O_PURE && i.useList == null) return killUnused(i);
 		match (i.op.opcode) {
 			BoolEq,
 			IntEq,
@@ -730,6 +732,7 @@ class SsaInstrReducer(context: SsaContext) extends SsaInstrMatcher {
 					}
 					i.setFactIf(Fact.O_NO_NULL_CHECK, Fact.O_PURE);
 					i.facts |= Fact.F_VALUE;
+					if (remove_pure_ops && i.facts.O_PURE && i.useList == null) return killUnused(i);
 					return lookupField(i, receiver, field);
 				}
 			}
@@ -1232,6 +1235,11 @@ class SsaInstrReducer(context: SsaContext) extends SsaInstrMatcher {
 		prev = i;
 		return i;
 	}
+	def killUnused(i_old: SsaInstr) -> SsaInstr {
+		i_old.kill();
+		i_old.remove();
+		return graph.nop();
+	}
 }
 
 // Performs control flow optimizations on a completed SsaGraph.
@@ -1911,15 +1919,23 @@ class SsaLoadOptimizer(context: SsaContext) {
 		pure.length = 0;
 		impure.length = 0;
 		var i = block.next;
+		for (i = block.next; SsaInstr.?(i); ()) {
+			var next = i.next;
+			match (i) {
+				instr: SsaApplyOp => {
+					var repl = optInstr(instr);
+					if (repl != null) {
+						any = true;
+						instr.replace(repl);
+						instr.remove();
+					}
+				}
+			}
+			i = next;
+		}
 		while (SsaApplyOp.?(i)) {
 			var instr = SsaApplyOp.!(i);
 			var next = instr.next;
-			var repl = optInstr(instr);
-			if (repl != null) {
-				any = true;
-				instr.replace(repl);
-				instr.remove();
-			}
 			i = next;
 		}
 	}
diff --git a/aeneas/test/SsaInstrReducerTest.v3 b/aeneas/test/SsaInstrReducerTest.v3
index 61a04db74..1ead48012 100644
--- a/aeneas/test/SsaInstrReducerTest.v3
+++ b/aeneas/test/SsaInstrReducerTest.v3
@@ -199,6 +199,7 @@ private class SsaInstrReducerTester(t: Tester) {
 		opt.optimize_nullchecks = optimize_nullchecks;
 		opt.optimize_inits = optimize_inits;
 		opt.optimize_bounds = optimize_bounds;
+		opt.remove_pure_ops = false; // TODO: test with removal of pure operations
 		return opt;
 	}
 	def recordConst(rtype: Type, vals: Array<Val>) -> SsaConst {
diff --git a/test/core/opt_load12.v3 b/test/core/opt_load12.v3
new file mode 100644
index 000000000..5ae48c416
--- /dev/null
+++ b/test/core/opt_load12.v3
@@ -0,0 +1,10 @@
+//@execute -1=33; 2=55
+class Foo(x: (int, int)) { }
+
+var f1 = Foo.new(33, 44);
+var f2 = Foo.new(55, 66);
+
+def main(a: int) -> int {
+	var f = if(a < 0, f1, f2);
+	return f.x.0;
+}