Warn when LLVM IR doesn't appear to generate symbols

Author: shepmaster

ui/frontend/.prettierignore

@@ -20,10 +20,12 @@ node_modules
 !HelpExample.tsx
 !Notifications.tsx
 !Output/Assembly.tsx
+!Output/LlvmIr.tsx
 !Output/OutputPrism.tsx
 !Output/PaneWithCode.tsx
 !Output/PaneWithMir.tsx
 !Output/SimplePane.tsx
+!Output/WarnAboutNoSymbols.tsx
 !PopButton.tsx
 !Prism.tsx
 !Stdin.tsx

ui/frontend/Output.tsx

@@ -14,6 +14,7 @@ import { useAppDispatch, useAppSelector } from './hooks';
 
 import * as styles from './Output.module.css';
 import Stdin from './Stdin';
+import LlvmIr from './Output/LlvmIr';
 
 const Tab: React.FC<TabProps> = ({ kind, focus, label, onClick, tabProps }) => {
   if (selectors.hasProperties(tabProps)) {
@@ -75,7 +76,7 @@ const Output: React.FC = () => {
           {focus === Focus.Miri && <SimplePane {...miri} kind="miri" />}
           {focus === Focus.MacroExpansion && <SimplePane {...macroExpansion} kind="macro-expansion" />}
           {focus === Focus.Asm && <Assembly />}
-          {focus === Focus.LlvmIr && <PaneWithCode {...llvmIr} kind="llvm-ir" />}
+          {focus === Focus.LlvmIr && <LlvmIr />}
           {focus === Focus.Mir && <PaneWithMir {...mir} kind="mir" />}
           {focus === Focus.Hir && <PaneWithMir {...hir} kind="hir" />}
           {focus === Focus.Wasm && <PaneWithCode {...wasm} kind="wasm" />}

ui/frontend/Output/Assembly.tsx

@@ -3,28 +3,20 @@ import React from 'react';
 import { useAppSelector } from '../hooks';
 import * as selectors from '../selectors';
 import PaneWithCode from './PaneWithCode';
-import Section from './Section';
+import WarnAboutNoSymbols from './WarnAboutNoSymbols';
 
 const Assembly: React.FC = () => {
   const assembly = useAppSelector((state) => state.output.assembly);
   const isAssemblyInProgress = useAppSelector(selectors.isAssemblyInProgressSelector);
   const hasAssemblySymbols = useAppSelector(selectors.hasAssemblySymbolsSelector);
 
-  const warnAboutNoSymbols = !isAssemblyInProgress && !hasAssemblySymbols;
-
   return (
     <PaneWithCode {...assembly} kind="asm">
-      {warnAboutNoSymbols ? (
-        <Section kind="warning" label="Warnings">
-          No symbols detected — they may have been optimized away.
-          {'\n'}
-          Add the <code>#[unsafe(no_mangle)]</code> attribute to
-          {'\n'}
-          functions you want to see assembly for. Generic functions
-          {'\n'}
-          only generate assembly when concrete types are provided.
-        </Section>
-      ) : null}
+      <WarnAboutNoSymbols
+        isInProgress={isAssemblyInProgress}
+        hasSymbols={hasAssemblySymbols}
+        name="assembly"
+      />
     </PaneWithCode>
   );
 };

ui/frontend/Output/LlvmIr.tsx

@@ -0,0 +1,24 @@
+import React from 'react';
+
+import { useAppSelector } from '../hooks';
+import * as selectors from '../selectors';
+import PaneWithCode from './PaneWithCode';
+import WarnAboutNoSymbols from './WarnAboutNoSymbols';
+
+const LlvmIr: React.FC = () => {
+  const llvmIr = useAppSelector((state) => state.output.llvmIr);
+  const isLlvmIrInProgress = useAppSelector(selectors.isLlvmIrInProgressSelector);
+  const hasLlvmIrSymbols = useAppSelector(selectors.hasLlvmIrSymbolsSelector);
+
+  return (
+    <PaneWithCode {...llvmIr} kind="llvm-ir">
+      <WarnAboutNoSymbols
+        isInProgress={isLlvmIrInProgress}
+        hasSymbols={hasLlvmIrSymbols}
+        name="LLVM IR"
+      />
+    </PaneWithCode>
+  );
+};
+
+export default LlvmIr;

ui/frontend/Output/WarnAboutNoSymbols.tsx

@@ -0,0 +1,35 @@
+import React from 'react';
+
+import Section from './Section';
+
+export interface WarnAboutNoSymbolsProps {
+  isInProgress: boolean;
+  hasSymbols: boolean;
+  name: string;
+}
+
+const WarnAboutNoSymbols: React.FC<WarnAboutNoSymbolsProps> = ({
+  isInProgress,
+  hasSymbols,
+  name,
+}) => {
+  const warnAboutNoSymbols = !isInProgress && !hasSymbols;
+
+  if (!warnAboutNoSymbols) {
+    return null;
+  }
+
+  return (
+    <Section kind="warning" label="Warnings">
+      No symbols detected — they may have been optimized away.
+      {'\n'}
+      Add the <code>#[unsafe(no_mangle)]</code> attribute to
+      {'\n'}
+      functions you want to see {name} for. Generic functions
+      {'\n'}
+      only generate {name} when concrete types are provided.
+    </Section>
+  );
+};
+
+export default WarnAboutNoSymbols;

ui/frontend/selectors/index.spec.ts

@@ -1,6 +1,10 @@
 import reducer from '../reducers';
 import { editCode } from '../reducers/code';
-import { hasAssemblySymbolsSelector, hasMainFunctionSelector } from './index';
+import {
+  hasAssemblySymbolsSelector,
+  hasLlvmIrSymbolsSelector,
+  hasMainFunctionSelector,
+} from './index';
 
 const buildState = (code: string) => reducer(undefined, editCode(code));
 
@@ -112,3 +116,30 @@ describe('checking for symbols in assembly output', () => {
     );
   });
 });
+
+const doHasLlvmIrSymbolsSelector = (code: string) => {
+  const state = reducer({ output: { llvmIr: { code, requestsInProgress: 0 } } }, { type: 'test' });
+  return hasLlvmIrSymbolsSelector(state);
+};
+
+describe('checking for symbols in LLVM IR output', () => {
+  test('empty code has no symbols', () => {
+    expect(doHasLlvmIrSymbolsSelector('')).toBe(false);
+  });
+
+  test('metadata is not a symbol', () => {
+    expect(
+      doHasLlvmIrSymbolsSelector('source_filename = "playground.d1ee58e2761c15fe-cgu.0"'),
+    ).toBe(false);
+    expect(doHasLlvmIrSymbolsSelector('!llvm.ident = !{!1}')).toBe(false);
+    expect(
+      doHasLlvmIrSymbolsSelector('!1 = !{!"rustc version 1.90.0-nightly (3048886e5 2025-07-30)"}'),
+    ).toBe(false);
+  });
+
+  test('a symbol is a symbol', () => {
+    expect(
+      doHasLlvmIrSymbolsSelector('define noundef i32 @add(i32 noundef %v) unnamed_addr #0 {'),
+    ).toBe(true);
+  });
+});

ui/frontend/selectors/index.ts

@@ -530,6 +530,18 @@ export const hasAssemblySymbolsSelector = createSelector(
   asm => !!asm.code?.match(ASSEMBLY_SYMBOLS_RE),
 );
 
+export const isLlvmIrInProgressSelector = createSelector(
+  (state: State) => state.output.llvmIr,
+  llvmIr => llvmIr.requestsInProgress > 0,
+);
+
+const LLVMIR_SYMBOLS_RE = /^define.*@.*{/m;
+
+export const hasLlvmIrSymbolsSelector = createSelector(
+  (state: State) => state.output.llvmIr,
+  llvmIr => !!llvmIr.code?.match(LLVMIR_SYMBOLS_RE),
+);
+
 export const themeSelector = createSelector(
   (state: State) => state,
   (state) => state.configuration.theme,