[PATCH] D122819: [FuncSpec] Cache code metrics for analyzed functions.

[Alexandros Lamprineas via Phabricator via llvm-commits]

labrinea created this revision.
labrinea added reviewers: ChuanqiXu, SjoerdMeijer.
Herald added subscribers: snehasish, ormris, hiraditya.
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This isn't expected to reduce compilation times as `max-iters` is set to one by default, but it helps with recursive functions that require higher iteration counts.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D122819

Files:
  llvm/lib/Transforms/IPO/FunctionSpecialization.cpp


Index: llvm/lib/Transforms/IPO/FunctionSpecialization.cpp
===================================================================
--- llvm/lib/Transforms/IPO/FunctionSpecialization.cpp
+++ llvm/lib/Transforms/IPO/FunctionSpecialization.cpp
@@ -21,8 +21,6 @@
 //   but that's off by default under an option.
 // - The cost-model could be further looked into (it mainly focuses on inlining
 //   benefits),
-// - We are not yet caching analysis results, but profiling and checking where
-//   extra compile time is spent didn't suggest this to be a problem.
 //
 // Ideas:
 // - With a function specialization attribute for arguments, we could have
@@ -281,6 +279,7 @@
   SmallPtrSet<Function *, 4> SpecializedFuncs;
   SmallPtrSet<Function *, 4> FullySpecialized;
   SmallVector<Instruction *> ReplacedWithConstant;
+  DenseMap<Function *, CodeMetrics> FunctionMetrics;
 
 public:
   FunctionSpecializer(SCCPSolver &Solver,
@@ -390,6 +389,19 @@
   // also in the cost model.
   unsigned NbFunctionsSpecialized = 0;
 
+  // Cache the CodeMetrics for function \p F.
+  void analyzeFunction(Function *F) {
+    SmallPtrSet<const Value *, 32> EphValues;
+    CodeMetrics::collectEphemeralValues(F, &(GetAC)(*F), EphValues);
+    CodeMetrics &Metrics = FunctionMetrics[F];
+    for (BasicBlock &BB : *F)
+      Metrics.analyzeBasicBlock(&BB, (GetTTI)(*F), EphValues);
+
+    LLVM_DEBUG(dbgs() << "FnSpecialization: Code size of function "
+                      << F->getName() << " is " << Metrics.NumInsts
+                      << " instructions\n");
+  }
+
   /// Clone the function \p F and remove the ssa_copy intrinsics added by
   /// the SCCPSolver in the cloned version.
   Function *cloneCandidateFunction(Function *F, ValueToValueMapTy &Mappings) {
@@ -528,12 +540,10 @@
 
   /// Compute and return the cost of specializing function \p F.
   InstructionCost getSpecializationCost(Function *F) {
-    // Compute the code metrics for the function.
-    SmallPtrSet<const Value *, 32> EphValues;
-    CodeMetrics::collectEphemeralValues(F, &(GetAC)(*F), EphValues);
-    CodeMetrics Metrics;
-    for (BasicBlock &BB : *F)
-      Metrics.analyzeBasicBlock(&BB, (GetTTI)(*F), EphValues);
+    auto I = FunctionMetrics.insert({F, CodeMetrics()});
+    CodeMetrics &Metrics = I.first->second;
+    if (I.second)
+      analyzeFunction(F);
 
     // If the code metrics reveal that we shouldn't duplicate the function, we
     // shouldn't specialize it. Set the specialization cost to Invalid.


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