[PGO] Remove redundant VP instrumentation

LLVM optimization passes may reduce a profiled target expression
to a constant. Removing runtime calls at such instrumentation points
would help speedup the runtime of the instrumented program.

llvm-svn: 266229

2 files changed, 35 insertions, 0 deletions

diff --git a/llvm/lib/Transforms/Scalar/ADCE.cpp b/llvm/lib/Transforms/Scalar/ADCE.cpp
index d94f83d66c4..579e60f76da 100644
--- a/llvm/lib/Transforms/Scalar/ADCE.cpp
+++ b/llvm/lib/Transforms/Scalar/ADCE.cpp
@@ -27,6 +27,7 @@
 #include "llvm/IR/Instructions.h"
 #include "llvm/IR/IntrinsicInst.h"
 #include "llvm/Pass.h"
+#include "llvm/ProfileData/InstrProf.h"
 #include "llvm/Transforms/Scalar.h"
 using namespace llvm;
 
@@ -61,6 +62,17 @@ static void collectLiveScopes(const DILocation &DL,
     collectLiveScopes(*IA, AliveScopes);
 }
 
+// Check if this instruction is a runtime call for value profiling and
+// if it's instrumenting a constant.
+static bool isInstrumentsConstant(Instruction &I) {
+  if (CallInst *CI = dyn_cast<CallInst>(&I))
+    if (Function *Callee = CI->getCalledFunction())
+      if (Callee->getName().equals(getInstrProfValueProfFuncName()))
+        if (isa<Constant>(CI->getArgOperand(0)))
+          return true;
+  return false;
+}
+
 static bool aggressiveDCE(Function& F) {
   SmallPtrSet<Instruction*, 32> Alive;
   SmallVector<Instruction*, 128> Worklist;
@@ -68,6 +80,10 @@ static bool aggressiveDCE(Function& F) {
   // Collect the set of "root" instructions that are known live.
   for (Instruction &I : instructions(F)) {
     if (isa<TerminatorInst>(I) || I.isEHPad() || I.mayHaveSideEffects()) {
+      // Skip any value profile instrumentation calls if they are
+      // instrumenting constants.
+      if (isInstrumentsConstant(I))
+        continue;
       Alive.insert(&I);
       Worklist.push_back(&I);
     }
diff --git a/llvm/test/Transforms/ADCE/delete-profiling-calls-to-constant.ll b/llvm/test/Transforms/ADCE/delete-profiling-calls-to-constant.ll
new file mode 100644
index 00000000000..a61e8f8cacc
--- /dev/null
+++ b/llvm/test/Transforms/ADCE/delete-profiling-calls-to-constant.ll
@@ -0,0 +1,19 @@
+; RUN: opt < %s -adce | FileCheck %s
+; RUN: opt < %s -passes=adce | FileCheck %s
+
+; Verify that a call to instrument a constant is deleted.
+
+@__profc_foo = private global [1 x i64] zeroinitializer, section "__llvm_prf_cnts", align 8
+@__profd_foo = private global { i64, i64, i64*, i8*, i8*, i32, [1 x i16] } { i64 6699318081062747564, i64 0, i64* getelementptr inbounds ([1 x i64], [1 x i64]* @__profc_foo, i32 0, i32 0), i8* bitcast (i32 ()* @foo to i8*), i8* null, i32 1, [1 x i16] [i16 1] }, section "__llvm_prf_data", align 8
+
+define i32 @foo() {
+; CHECK-NOT: __llvm_profile_instrument_target
+entry:
+  tail call void @__llvm_profile_instrument_target(i64 ptrtoint (i32 (i32)* @bar to i64), i8* bitcast ({ i64, i64, i64*, i8*, i8*, i32, [1 x i16] }* @__profd_foo to i8*), i32 0)
+  %call = tail call i32 @bar(i32 21)
+  ret i32 %call
+}
+
+declare i32 @bar(i32)
+
+declare void @__llvm_profile_instrument_target(i64, i8*, i32)