Reduce bytecode impact of mixed requirement views

When mixing optional and required views we used to skip storing into the 'id' local for optional views.

    id = R.id.one;
    View one = root.findViewById(id);
    if (one == null) break missingId;

    View two = root.findViewById(R.id.two);

This uses separate registers for R.id.one and R.id.two requiring one more register in total for the method.

    .registers 4

    const v0, 0x102001a

    .line 19
    invoke-virtual {p0, v0}, Landroid/view/View;->findViewById(I)Landroid/view/View;

    move-result-object v1

    if-nez v1, :cond_a

    goto :goto_1f

    :cond_a
    const v2, 0x102003c

    .line 22
    invoke-virtual {p0, v2}, Landroid/view/View;->findViewById(I)Landroid/view/View;

When the 'id' local is present, unconditionally storing the next ID into that local allows the register to be reused.

    id = R.id.one;
    View one = root.findViewById(id);
    if (one == null) break missingId;

    id = R.id.two;
    View two = root.findViewById(id);

Produces:

    .registers 3

    const v0, 0x102001a

    .line 19
    invoke-virtual {p0, v0}, Landroid/view/View;->findViewById(I)Landroid/view/View;

    move-result-object v1

    if-nez v1, :cond_a

    goto :goto_1f

    :cond_a
    const v0, 0x102003c

    .line 22
    invoke-virtual {p0, v0}, Landroid/view/View;->findViewById(I)Landroid/view/View;

Bug: 128314294
Test: ../base/bazel/bazel test //tools/base/build-system/integration-test/databinding:tests //tools/data-binding/...
Change-Id: I6408d214ba549c443d3743151636eef391083d26

1 files changed, 6 insertions, 2 deletions

diff --git a/compilerCommon/src/main/kotlin/android/databinding/tool/writer/ViewBinderGenerateJava.kt b/compilerCommon/src/main/kotlin/android/databinding/tool/writer/ViewBinderGenerateJava.kt
index ca545132..a6492e54 100644
--- a/compilerCommon/src/main/kotlin/android/databinding/tool/writer/ViewBinderGenerateJava.kt
+++ b/compilerCommon/src/main/kotlin/android/databinding/tool/writer/ViewBinderGenerateJava.kt
@@ -246,7 +246,8 @@ private class JavaFileGenerator(
         /** Non-null when error-handling is being generated. */
         val id: String?
 
-        if (nonRootBindings.any { it.isRequired }) {
+        val hasRequiredBindings = nonRootBindings.any { it.isRequired }
+        if (hasRequiredBindings) {
             addComment("The body of this method is generated in a way you would not otherwise write.")
             addComment("This is done to optimize the compiled bytecode for size and performance.")
 
@@ -274,8 +275,11 @@ private class JavaFileGenerator(
             val viewInitializer = if (binding === rootBinding) {
                 // If this corresponds to the root binding, we can re-use the input View argument.
                 rootParam.asViewReference(viewType)
-            } else if (binding.isRequired) {
+            } else if (hasRequiredBindings) {
                 // Place the id value first into the local in case it's needed for error handling.
+                // We do this unconditionally (even for optional bindings) so that the Dalvik
+                // bytecode re-uses the same register rather than using one for optional IDs and
+                // one for required IDs.
                 addStatement("$id = $L", binding.id.asCode())
                 CodeBlock.of("$N.findViewById($id)", rootParam)
             } else {