[Instrumentation] Remove -pgo-instr-old-cfg-hashing (llvm#77357)

It's been more than 3 years since -pgo-instr-old-cfg-hashing was
introduced by:

  commit 120e66b
  Author: Hiroshi Yamauchi <yamauchi@google.com>
  Date:   Tue Jul 28 10:09:49 2020 -0700

I don't think anyone really cares about the ability to use the old CFG
hashing at this point.

llvm/lib/Transforms/Instrumentation/PGOInstrumentation.cpp

@@ -330,10 +330,6 @@ extern cl::opt<std::string> ViewBlockFreqFuncName;
 extern cl::opt<InstrProfCorrelator::ProfCorrelatorKind> ProfileCorrelate;
 } // namespace llvm
 
-static cl::opt<bool>
-    PGOOldCFGHashing("pgo-instr-old-cfg-hashing", cl::init(false), cl::Hidden,
-                     cl::desc("Use the old CFG function hashing"));
-
 // Return a string describing the branch condition that can be
 // used in static branch probability heuristics:
 static std::string getBranchCondString(Instruction *TI) {
@@ -635,34 +631,25 @@ void FuncPGOInstrumentation<Edge, BBInfo>::computeCFGHash() {
   JC.update(Indexes);
 
   JamCRC JCH;
-  if (PGOOldCFGHashing) {
-    // Hash format for context sensitive profile. Reserve 4 bits for other
-    // information.
-    FunctionHash = (uint64_t)SIVisitor.getNumOfSelectInsts() << 56 |
-                   (uint64_t)ValueSites[IPVK_IndirectCallTarget].size() << 48 |
-                   //(uint64_t)ValueSites[IPVK_MemOPSize].size() << 40 |
-                   (uint64_t)MST.numEdges() << 32 | JC.getCRC();
+  // The higher 32 bits.
+  auto updateJCH = [&JCH](uint64_t Num) {
+    uint8_t Data[8];
+    support::endian::write64le(Data, Num);
+    JCH.update(Data);
+  };
+  updateJCH((uint64_t)SIVisitor.getNumOfSelectInsts());
+  updateJCH((uint64_t)ValueSites[IPVK_IndirectCallTarget].size());
+  updateJCH((uint64_t)ValueSites[IPVK_MemOPSize].size());
+  if (BCI) {
+    updateJCH(BCI->getInstrumentedBlocksHash());
   } else {
-    // The higher 32 bits.
-    auto updateJCH = [&JCH](uint64_t Num) {
-      uint8_t Data[8];
-      support::endian::write64le(Data, Num);
-      JCH.update(Data);
-    };
-    updateJCH((uint64_t)SIVisitor.getNumOfSelectInsts());
-    updateJCH((uint64_t)ValueSites[IPVK_IndirectCallTarget].size());
-    updateJCH((uint64_t)ValueSites[IPVK_MemOPSize].size());
-    if (BCI) {
-      updateJCH(BCI->getInstrumentedBlocksHash());
-    } else {
-      updateJCH((uint64_t)MST.numEdges());
-    }
-
-    // Hash format for context sensitive profile. Reserve 4 bits for other
-    // information.
-    FunctionHash = (((uint64_t)JCH.getCRC()) << 28) + JC.getCRC();
+    updateJCH((uint64_t)MST.numEdges());
   }
 
+  // Hash format for context sensitive profile. Reserve 4 bits for other
+  // information.
+  FunctionHash = (((uint64_t)JCH.getCRC()) << 28) + JC.getCRC();
+
   // Reserve bit 60-63 for other information purpose.
   FunctionHash &= 0x0FFFFFFFFFFFFFFF;
   if (IsCS)
@@ -672,10 +659,8 @@ void FuncPGOInstrumentation<Edge, BBInfo>::computeCFGHash() {
                     << ", Selects = " << SIVisitor.getNumOfSelectInsts()
                     << ", Edges = " << MST.numEdges() << ", ICSites = "
                     << ValueSites[IPVK_IndirectCallTarget].size());
-  if (!PGOOldCFGHashing) {
-    LLVM_DEBUG(dbgs() << ", Memops = " << ValueSites[IPVK_MemOPSize].size()
-                      << ", High32 CRC = " << JCH.getCRC());
-  }
+  LLVM_DEBUG(dbgs() << ", Memops = " << ValueSites[IPVK_MemOPSize].size()
+                    << ", High32 CRC = " << JCH.getCRC());
   LLVM_DEBUG(dbgs() << ", Hash = " << FunctionHash << "\n";);
 
   if (PGOTraceFuncHash != "-" && F.getName().contains(PGOTraceFuncHash))

llvm/test/Transforms/PGOProfile/Inputs/multiple_hash_profile.proftext

@@ -9,16 +9,6 @@ _Z3fooi
 18
 12
 
-# For -pgo-instr-old-cfg-hashing=true
-_Z3fooi
-# Func Hash:
-72057606922829823
-# Num Counters:
-2
-# Counter Values:
-18
-6
-
 _Z3fooi
 # Func Hash:
 12884901887
@@ -36,29 +26,10 @@ _Z3bari
 0
 0
 
-# For -pgo-instr-old-cfg-hashing=true
-_Z3bari
-# Func Hash:
-72057606922829823
-# Num Counters:
-2
-# Counter Values:
-0
-0
-
 _Z4m2f1v
 # Func Hash:
 742261418966908927
 # Num Counters:
 1
 # Counter Values:
 1
-
-# For -pgo-instr-old-cfg-hashing=true
-_Z4m2f1v
-# Func Hash:
-12884901887
-# Num Counters:
-1
-# Counter Values:
-1

llvm/test/Transforms/PGOProfile/multiple_hash_profile.ll

@@ -1,6 +1,5 @@
 ; RUN: llvm-profdata merge %S/Inputs/multiple_hash_profile.proftext -o %t.profdata
 ; RUN: opt < %s -passes=pgo-instr-use -pgo-test-profile-file=%t.profdata -S | FileCheck %s
-; RUN: opt < %s -passes=pgo-instr-use -pgo-test-profile-file=%t.profdata -pgo-instr-old-cfg-hashing=true -S | FileCheck -check-prefix=CHECKOLDHASH %s
 target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
 target triple = "x86_64-unknown-linux-gnu"
 
@@ -29,9 +28,6 @@ entry:
 ; CHECK: %mul.i = select i1 %cmp.i, i32 1, i32 %i
 ; CHECK-SAME: !prof ![[BW:[0-9]+]]
 ; CHECK: ![[BW]] = !{!"branch_weights", i32 12, i32 6}
-; CHECKOLDHASH: %mul.i = select i1 %cmp.i, i32 1, i32 %i
-; CHECKOLDHASH-SAME: !prof ![[BW:[0-9]+]]
-; CHECKOLDHASH: ![[BW]] = !{!"branch_weights", i32 6, i32 12}
   %retval.0.i = mul nsw i32 %mul.i, %i
   ret i32 %retval.0.i
 }