internal/shader: optimization: remove unnecessary local variables

Updates #2034
Updates #2188

internal/shader/expr.go

@@ -534,32 +534,12 @@ func (cs *compileState) parseExpr(block *block, expr ast.Expr, markLocalVariable
 				return nil, nil, nil, false
 			}
 
-			idx := block.totalLocalVariableNum()
-			block.vars = append(block.vars, variable{
-				typ: t,
-			})
-
-			// Calling the function should be done eariler to treat out-params correctly.
-			stmts = append(stmts, shaderir.Stmt{
-				Type: shaderir.Assign,
-				Exprs: []shaderir.Expr{
-					{
-						Type:  shaderir.LocalVariable,
-						Index: idx,
-					},
-					{
-						Type:  shaderir.Call,
-						Exprs: append([]shaderir.Expr{callee}, args...),
-					},
-				},
-			})
-
 			// The actual expression here is just a local variable that includes the result of the
 			// function call.
 			return []shaderir.Expr{
 				{
-					Type:  shaderir.LocalVariable,
-					Index: idx,
+					Type:  shaderir.Call,
+					Exprs: append([]shaderir.Expr{callee}, args...),
 				},
 			}, []shaderir.Type{t}, stmts, true
 		}

internal/shader/testdata/call.expected.vs

@@ -2,9 +2,7 @@ vec2 F0(in vec2 l0);
 vec2 F1(in vec2 l0);
 
 vec2 F0(in vec2 l0) {
-	vec2 l1 = vec2(0);
-	l1 = F1(l0);
-	return l1;
+	return F1(l0);
 }
 
 vec2 F1(in vec2 l0) {

internal/shader/testdata/const4.expected.vs

@@ -12,13 +12,9 @@ float F1(in float l0) {
 }
 
 int F2(void) {
-	int l0 = 0;
-	l0 = F0(1);
-	return l0;
+	return F0(1);
 }
 
 float F3(void) {
-	float l0 = float(0);
-	l0 = F1(1.0);
-	return l0;
+	return F1(1.0);
 }

internal/shader/testdata/define2.expected.vs

@@ -4,13 +4,9 @@ vec2 F1(void);
 vec2 F0(void) {
 	vec2 l0 = vec2(0);
 	vec2 l1 = vec2(0);
-	vec2 l2 = vec2(0);
-	vec2 l3 = vec2(0);
-	l0 = F1();
-	l1 = (1.0) * (l0);
-	l2 = F1();
-	l3 = (l2) * (1.0);
-	return l1;
+	l0 = (1.0) * (F1());
+	l1 = (F1()) * (1.0);
+	return l0;
 }
 
 vec2 F1(void) {

internal/shader/testdata/for4.expected.vs

@@ -11,10 +11,8 @@ int F1(void) {
 	l0 = 0;
 	for (int l1 = 0; l1 < 10; l1++) {
 		int l2 = 0;
-		int l3 = 0;
 		l2 = F0(l1);
-		l3 = l2;
-		l0 = (l0) + (l3);
+		l0 = (l0) + (l2);
 	}
 	l2 = 0;
 	l0 = (l0) + (l2);

internal/shader/testdata/for5.expected.fs

@@ -14,16 +14,12 @@ void main(void) {
 	l0 = 0;
 	for (int l1 = 0; l1 < 10; l1++) {
 		int l2 = 0;
-		int l3 = 0;
 		l2 = F0(l1);
-		l3 = l2;
-		l0 = (l0) + (l3);
-		for (int l4 = 0; l4 < 10; l4++) {
-			int l5 = 0;
-			int l6 = 0;
-			l5 = F0(l4);
-			l6 = l5;
-			l0 = (l0) + (l6);
+		l0 = (l0) + (l2);
+		for (int l3 = 0; l3 < 10; l3++) {
+			int l4 = 0;
+			l4 = F0(l3);
+			l0 = (l0) + (l4);
 		}
 	}
 	l2 = 0;

internal/shader/testdata/for5.expected.vs

@@ -15,16 +15,12 @@ void main(void) {
 	l0 = 0;
 	for (int l1 = 0; l1 < 10; l1++) {
 		int l2 = 0;
-		int l3 = 0;
 		l2 = F0(l1);
-		l3 = l2;
-		l0 = (l0) + (l3);
-		for (int l4 = 0; l4 < 10; l4++) {
-			int l5 = 0;
-			int l6 = 0;
-			l5 = F0(l4);
-			l6 = l5;
-			l0 = (l0) + (l6);
+		l0 = (l0) + (l2);
+		for (int l3 = 0; l3 < 10; l3++) {
+			int l4 = 0;
+			l4 = F0(l3);
+			l0 = (l0) + (l4);
 		}
 	}
 	l2 = 0;

internal/shader/testdata/number.expected.vs

@@ -8,25 +8,17 @@ void F5(void);
 vec2 F0(void) {
 	float l0 = float(0);
 	float l1 = float(0);
-	float l2 = float(0);
-	float l3 = float(0);
-	l0 = F2();
-	l1 = (l0) * (1.0);
-	l2 = F2();
-	l3 = (1.0) * (l2);
-	return vec2(l1, l3);
+	l0 = (F2()) * (1.0);
+	l1 = (1.0) * (F2());
+	return vec2(l0, l1);
 }
 
 vec2 F1(void) {
 	float l0 = float(0);
 	float l1 = float(0);
-	float l2 = float(0);
-	float l3 = float(0);
-	l0 = F2();
-	l1 = (l0) * (1.0);
-	l2 = F2();
-	l3 = (1.0) * (l2);
-	return vec2(l1, l3);
+	l0 = (F2()) * (1.0);
+	l1 = (1.0) * (F2());
+	return vec2(l0, l1);
 }
 
 float F2(void) {