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site/frontend/src/pages/compare/compile/common.ts

@@ -245,13 +245,12 @@ export function transformDataForBackendComparison(
     }
   }
 
-  const transformed = [];
-  benchmarkMap.forEach((entry) => {
+  return Array.from(benchmarkMap, ([_, entry]) => {
     const comparison: CompileBenchmarkComparison = {
       benchmark: entry.benchmark,
       profile: entry.profile,
       scenario: entry.scenario,
-      // Treat the backend as LLVM
+      // Treat LLVM as the baseline
       backend: "llvm",
       comparison: {
         statistics: [entry.llvm, entry.cranelift],
@@ -260,8 +259,6 @@ export function transformDataForBackendComparison(
         significance_threshold: 1.0,
       },
     };
-    transformed.push(comparison);
+    return comparison;
   });
-
-  return transformed;
 }

site/frontend/src/pages/compare/compile/compile-page.vue

@@ -216,22 +216,28 @@ const quickLinksKey = ref(0);
 const filter = ref(loadFilterFromUrl(urlParams, defaultCompileFilter));
 
 // Should we use the backend as the source of before/after data?
-const selfCompareBackend = computed(
-  () => comparesIdenticalCommits.value && filter.value.selfCompareBackend
-);
+const selfCompareBackend = computed(() => {
+  const hasMultipleBackends =
+    new Set(props.data.compile_comparisons.map((c) => c.backend)).size > 1;
+  return (
+    comparesIdenticalCommits.value &&
+    filter.value.selfCompareBackend &&
+    hasMultipleBackends
+  );
+});
 
 function exportData() {
   exportToMarkdown(comparisons.value, filter.value.showRawData);
 }
 
-// Are we currently comparing the same commit against each other?
+// Are we currently comparing the same commit in the before/after toolchains?
 const comparesIdenticalCommits = computed(() => {
   return props.data.a.commit === props.data.b.commit;
 });
 const benchmarkMap = createCompileBenchmarkMap(props.data);
 
-// Artificially restructure the data to create a comparison between backends
 const compileComparisons = computed(() => {
+  // If requested, artificially restructure the data to create a comparison between backends
   if (selfCompareBackend.value) {
     return transformDataForBackendComparison(props.data.compile_comparisons);
   } else {
@@ -258,8 +264,11 @@ const filteredSummary = computed(() => computeSummary(comparisons.value));
     :selected-metric="selector.stat"
     :metrics="benchmarkInfo.compile_metrics"
   />
-  <div v-if="comparesIdenticalCommits">
-    Self-compare backend:
+  <div
+    v-if="comparesIdenticalCommits"
+    :title="`Compare codegen backends for commit '${props.data.a.commit}'`"
+  >
+    Compare codegen backends for this commit:
     <input
       type="checkbox"
       :checked="selfCompareBackend"
@@ -275,7 +284,8 @@ const filteredSummary = computed(() => computeSummary(comparisons.value));
   <OverallSummary :summary="filteredSummary" />
   <Aggregations :cases="comparisons" />
   <div class="warning" v-if="selfCompareBackend">
-    Comparing Cranelift against LLVM baseline!
+    Note: comparing results of the baseline LLVM backend to the Cranelift
+    backend.
   </div>
   <Benchmarks
     :data="data"