[llvm] [IR][TLI] Cache getLibFunc() result on Function (NFC) (PR #72867)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-analysis

Author: Nikita Popov (nikic)

<details>
<summary>Changes</summary>

Cache the result of the TLI libfunc lookup in the Function object. This only caches the actual lookup of the LibFunc in the TLI map, but not the prototype validation, as that might differ between different TLI instances.

This uses the existing mechanism for invalidating the intrinsic ID when the function name changes. The libfunc will be invalidated in that case as well.

This results in a small compile-time improvement: http://llvm-compile-time-tracker.com/compare.php?from=a2e1de193477e7d92ec5c0a2ecd17a622cbf7aed&to=125c1c7aa60d73a3b041e9a011ff1d41c3d6194b&stat=instructions:u

I don't believe this increases the size of Function on 64bit (which currently has a trailing `bool` member), and I don't think we would particularly care if it did, as Functions are uncommon as Values go.

---
Full diff: https://github.com/llvm/llvm-project/pull/72867.diff


3 Files Affected:

- (modified) llvm/include/llvm/IR/Function.h (+9) 
- (modified) llvm/lib/Analysis/TargetLibraryInfo.cpp (+9-2) 
- (modified) llvm/lib/IR/Function.cpp (+1) 


``````````diff
diff --git a/llvm/include/llvm/IR/Function.h b/llvm/include/llvm/IR/Function.h
index 955a4fca6f86f7e..0089fd7d5d8788d 100644
--- a/llvm/include/llvm/IR/Function.h
+++ b/llvm/include/llvm/IR/Function.h
@@ -48,9 +48,11 @@ class AssemblyAnnotationWriter;
 class Constant;
 struct DenormalMode;
 class DISubprogram;
+enum LibFunc : unsigned;
 class LLVMContext;
 class Module;
 class raw_ostream;
+class TargetLibraryInfoImpl;
 class Type;
 class User;
 class BranchProbabilityInfo;
@@ -120,6 +122,13 @@ class LLVM_EXTERNAL_VISIBILITY Function : public GlobalObject,
   void setIsNewDbgInfoFormat(bool NewVal);
 
 private:
+  friend class TargetLibraryInfoImpl;
+
+  /// Cache for TLI::getLibFunc() result without prototype validation.
+  /// -1 if uninitialized. NotLibFunc if definitely not lib func.
+  /// Otherwise may be libfunc if prototype validation passes.
+  mutable LibFunc LibFuncCache = LibFunc(-1);
+
   void CheckLazyArguments() const {
     if (hasLazyArguments())
       BuildLazyArguments();
diff --git a/llvm/lib/Analysis/TargetLibraryInfo.cpp b/llvm/lib/Analysis/TargetLibraryInfo.cpp
index 7b38583e9bc75f0..1037368169bbaad 100644
--- a/llvm/lib/Analysis/TargetLibraryInfo.cpp
+++ b/llvm/lib/Analysis/TargetLibraryInfo.cpp
@@ -1138,8 +1138,15 @@ bool TargetLibraryInfoImpl::getLibFunc(const Function &FDecl,
   const Module *M = FDecl.getParent();
   assert(M && "Expecting FDecl to be connected to a Module.");
 
-  return getLibFunc(FDecl.getName(), F) &&
-         isValidProtoForLibFunc(*FDecl.getFunctionType(), F, *M);
+  if (FDecl.LibFuncCache == LibFunc(-1))
+    if (!getLibFunc(FDecl.getName(), FDecl.LibFuncCache))
+      FDecl.LibFuncCache = NotLibFunc;
+
+  if (FDecl.LibFuncCache == NotLibFunc)
+    return false;
+
+  F = FDecl.LibFuncCache;
+  return isValidProtoForLibFunc(*FDecl.getFunctionType(), F, *M);
 }
 
 void TargetLibraryInfoImpl::disableAllFunctions() {
diff --git a/llvm/lib/IR/Function.cpp b/llvm/lib/IR/Function.cpp
index 49e0c1c5883c265..bff36b02c20246f 100644
--- a/llvm/lib/IR/Function.cpp
+++ b/llvm/lib/IR/Function.cpp
@@ -913,6 +913,7 @@ Intrinsic::ID Function::lookupIntrinsicID(StringRef Name) {
 }
 
 void Function::recalculateIntrinsicID() {
+  LibFuncCache = LibFunc(-1);
   StringRef Name = getName();
   if (!Name.startswith("llvm.")) {
     HasLLVMReservedName = false;

``````````

</details>


https://github.com/llvm/llvm-project/pull/72867