[llvm] r304452 - [PartialInlining] Emit branch info and profile data as remarks

[Xinliang David Li via llvm-commits]

Author: davidxl
Date: Thu Jun  1 13:58:50 2017
New Revision: 304452

URL: http://llvm.org/viewvc/llvm-project?rev=304452&view=rev
Log:
[PartialInlining] Emit branch info and profile data as remarks

This allows us to collect profile statistics to tune static 
branch prediction.

Differential Revision: http://reviews.llvm.org/D33746

Modified:
    llvm/trunk/lib/Transforms/Instrumentation/PGOInstrumentation.cpp
    llvm/trunk/test/Transforms/PGOProfile/branch1.ll

Modified: llvm/trunk/lib/Transforms/Instrumentation/PGOInstrumentation.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Instrumentation/PGOInstrumentation.cpp?rev=304452&r1=304451&r2=304452&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Instrumentation/PGOInstrumentation.cpp (original)
+++ llvm/trunk/lib/Transforms/Instrumentation/PGOInstrumentation.cpp Thu Jun  1 13:58:50 2017
@@ -182,6 +182,14 @@ static cl::opt<bool>
                   cl::desc("Use this option to turn on/off "
                            "memory intrinsic size profiling."));
 
+// Emit branch probability as optimization remarks.
+static cl::opt<bool>
+    EmitBranchProbability("pgo-emit-branch-prob", cl::init(false), cl::Hidden,
+                          cl::desc("When this option is on, the annotated "
+                                   "branch probability will be emitted as "
+                                   " optimization remarks: -Rpass-analysis="
+                                   "pgo-instr-use"));
+
 // Command line option to turn on CFG dot dump after profile annotation.
 // Defined in Analysis/BlockFrequencyInfo.cpp:  -pgo-view-counts
 extern cl::opt<bool> PGOViewCounts;
@@ -192,6 +200,39 @@ extern cl::opt<std::string> ViewBlockFre
 
 namespace {
 
+// Return a string describing the branch condition that can be
+// used in static branch probability heuristics:
+std::string getBranchCondString(Instruction *TI) {
+  BranchInst *BI = dyn_cast<BranchInst>(TI);
+  if (!BI || !BI->isConditional())
+    return std::string();
+
+  Value *Cond = BI->getCondition();
+  ICmpInst *CI = dyn_cast<ICmpInst>(Cond);
+  if (!CI)
+    return std::string();
+
+  std::string result;
+  raw_string_ostream OS(result);
+  OS << CmpInst::getPredicateName(CI->getPredicate()) << "_";
+  CI->getOperand(0)->getType()->print(OS, true);
+
+  Value *RHS = CI->getOperand(1);
+  ConstantInt *CV = dyn_cast<ConstantInt>(RHS);
+  if (CV) {
+    if (CV->isZero())
+      OS << "_Zero";
+    else if (CV->isOne())
+      OS << "_One";
+    else if (CV->isAllOnesValue())
+      OS << "_MinusOne";
+    else
+      OS << "_Const";
+  }
+  OS.flush();
+  return result;
+}
+
 /// The select instruction visitor plays three roles specified
 /// by the mode. In \c VM_counting mode, it simply counts the number of
 /// select instructions. In \c VM_instrument mode, it inserts code to count
@@ -1424,6 +1465,29 @@ void setProfMetadata(Module *M, Instruct
         for (const auto &W : Weights) { dbgs() << W << " "; }
         dbgs() << "\n";);
   TI->setMetadata(llvm::LLVMContext::MD_prof, MDB.createBranchWeights(Weights));
+  if (EmitBranchProbability) {
+    std::string BrCondStr = getBranchCondString(TI);
+    if (BrCondStr.empty())
+      return;
+
+    unsigned WSum =
+        std::accumulate(Weights.begin(), Weights.end(), 0,
+                        [](unsigned w1, unsigned w2) { return w1 + w2; });
+    uint64_t TotalCount =
+        std::accumulate(EdgeCounts.begin(), EdgeCounts.end(), 0,
+                        [](uint64_t c1, uint64_t c2) { return c1 + c2; });
+    BranchProbability BP(Weights[0], WSum);
+    std::string BranchProbStr;
+    raw_string_ostream OS(BranchProbStr);
+    OS << BP;
+    OS << " (total count : " << TotalCount << ")";
+    OS.flush();
+    Function *F = TI->getParent()->getParent();
+    emitOptimizationRemarkAnalysis(
+        F->getContext(), "pgo-use-annot", *F, TI->getDebugLoc(),
+        Twine(BrCondStr) +
+            " is true with probability : " + Twine(BranchProbStr));
+  }
 }
 
 template <> struct GraphTraits<PGOUseFunc *> {

Modified: llvm/trunk/test/Transforms/PGOProfile/branch1.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/PGOProfile/branch1.ll?rev=304452&r1=304451&r2=304452&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/PGOProfile/branch1.ll (original)
+++ llvm/trunk/test/Transforms/PGOProfile/branch1.ll Thu Jun  1 13:58:50 2017
@@ -15,6 +15,9 @@
 ; RUN: opt < %s -passes=pgo-instr-use -pgo-test-profile-file=%t.profdata -S | FileCheck %s --check-prefix=USE
 ; RUN: opt < %s -passes=pgo-instr-use -pgo-test-profile-file=%t.l.profdata -S | FileCheck %s --check-prefix=USE-LARGE
 
+; RUN: opt < %s -pgo-instr-use -pgo-test-profile-file=%t.profdata -pass-remarks-analysis=pgo-use-annot -pgo-emit-branch-prob -S 2>&1| FileCheck %s --check-prefix=ANALYSIS
+; RUN: opt < %s -passes=pgo-instr-use -pgo-test-profile-file=%t.profdata -pass-remarks-analysis=pgo-use-annot -pgo-emit-branch-prob -S 2>&1| FileCheck %s --check-prefix=ANALYSIS
+
 target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
 target triple = "x86_64-unknown-linux-gnu"
 ; GEN-DARWIN-LINKONCE: target triple = "x86_64-apple-darwin"
@@ -54,3 +57,5 @@ if.end:
 ; USE-DAG: {{![0-9]+}} = !{i32 1, !"ProfileSummary", {{![0-9]+}}}
 ; USE-DAG: {{![0-9]+}} = !{!"DetailedSummary", {{![0-9]+}}}
 ; USE-DAG: ![[FUNC_ENTRY_COUNT]] = !{!"function_entry_count", i64 3}
+
+; ANALYSIS:remark: <unknown>:0:0: sgt_i32_Zero {{.*}}66.67% (total count : 3)