[PATCH] D122336: [InstrProfiling] No runtime hook for unused funcs

[Gulfem Savrun Yeniceri via Phabricator via cfe-commits]

gulfem created this revision.
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CoverageMappingModuleGen generates a coverage mapping record
even for unused functions with internal linkage, e.g.
static int foo() { return 100; }
Clang frontend eliminates such functions, but InstrProfiling pass
still pulls in profile runtime since there is a coverage record.
Fuchsia uses runtime counter relocation, and pulling in profile
runtime for unused functions causes a linker error:
undefined hidden symbol: __llvm_profile_counter_bias.
Since 389dc94d4be7 <https://reviews.llvm.org/rG389dc94d4be7a75c243528981a25260c1c7a6103>, we do not hook profile runtime for the binaries
that none of its translation units have been instrumented in Fuchsia.
This patch extends that for the instrumented binaries that
consist of only unused functions.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D122336

Files:
  clang/test/CoverageMapping/unused_function_no_runtime_hook.cpp
  llvm/lib/Transforms/Instrumentation/InstrProfiling.cpp


Index: llvm/lib/Transforms/Instrumentation/InstrProfiling.cpp
===================================================================
--- llvm/lib/Transforms/Instrumentation/InstrProfiling.cpp
+++ llvm/lib/Transforms/Instrumentation/InstrProfiling.cpp
@@ -558,16 +558,20 @@
   TT = Triple(M.getTargetTriple());
 
   bool MadeChange = false;
-
-  // Emit the runtime hook even if no counters are present.
-  if (needsRuntimeHookUnconditionally(TT))
+  bool NeedsRuntimeHook = needsRuntimeHookUnconditionally(TT);
+  if (NeedsRuntimeHook)
     MadeChange = emitRuntimeHook();
 
   // Improve compile time by avoiding linear scans when there is no work.
   GlobalVariable *CoverageNamesVar =
       M.getNamedGlobal(getCoverageUnusedNamesVarName());
-  if (!containsProfilingIntrinsics(M) && !CoverageNamesVar)
-    return MadeChange;
+  if (!containsProfilingIntrinsics(M)) {
+    if (!CoverageNamesVar) {
+      return MadeChange;
+    } else if (!NeedsRuntimeHook) {
+      return MadeChange;
+    }
+  }
 
   // We did not know how many value sites there would be inside
   // the instrumented function. This is counting the number of instrumented
Index: clang/test/CoverageMapping/unused_function_no_runtime_hook.cpp
===================================================================
--- /dev/null
+++ clang/test/CoverageMapping/unused_function_no_runtime_hook.cpp
@@ -0,0 +1,6 @@
+// RUN: %clang -target x86_64-unknown-fuchsia -fprofile-instr-generate -fcoverage-mapping -emit-llvm -S %s -o - | FileCheck %s
+
+// CHECK-NOT: @__llvm_profile_runtime
+static int f0() {
+  return 100;
+}


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