[BOLT] Support pre-aggregated returns

bolt/include/bolt/Profile/DataAggregator.h

@@ -109,6 +109,7 @@ class DataAggregator : public DataReader {
     static constexpr const uint64_t BR_ONLY = -1ULL;
     static constexpr const uint64_t FT_ONLY = -1ULL;
     static constexpr const uint64_t FT_EXTERNAL_ORIGIN = -2ULL;
+    static constexpr const uint64_t BR_EXTERNAL_RETURN = -3ULL;
 
     uint64_t Branch;
     uint64_t From;
@@ -388,7 +389,7 @@ class DataAggregator : public DataReader {
   /// File format syntax:
   /// E <event>
   /// S <start> <count>
-  /// T <start> <end> <ft_end> <count>
+  /// [TR] <start> <end> <ft_end> <count>
   /// B <start> <end> <count> <mispred_count>
   /// [Ff] <start> <end> <count>
   ///
@@ -403,6 +404,7 @@ class DataAggregator : public DataReader {
   ///       jump to the block
   /// T - an aggregated trace: branch from <start> to <end> with a fall-through
   ///       to <ft_end>
+  /// R - an aggregated trace originating at a return
   ///
   /// <id> - build id of the object containing the address. We can skip it for
   /// the main binary and use "X" for an unknown object. This will save some
@@ -532,6 +534,9 @@ inline raw_ostream &operator<<(raw_ostream &OS,
   case DataAggregator::Trace::FT_ONLY:
   case DataAggregator::Trace::FT_EXTERNAL_ORIGIN:
     break;
+  case DataAggregator::Trace::BR_EXTERNAL_RETURN:
+    OS << "0 -> ";
+    break;
   default:
     OS << Twine::utohexstr(T.Branch) << " -> ";
   }

bolt/lib/Profile/DataAggregator.cpp

@@ -1204,6 +1204,7 @@ std::error_code DataAggregator::parseAggregatedLBREntry() {
     INVALID = 0,
     EVENT_NAME,        // E
     TRACE,             // T
+    RETURN,            // R
     SAMPLE,            // S
     BRANCH,            // B
     FT,                // F
@@ -1235,6 +1236,7 @@ std::error_code DataAggregator::parseAggregatedLBREntry() {
 
     Type = StringSwitch<AggregatedLBREntry>(Str)
                .Case("T", TRACE)
+               .Case("R", RETURN)
                .Case("S", SAMPLE)
                .Case("E", EVENT_NAME)
                .Case("B", BRANCH)
@@ -1248,7 +1250,7 @@ std::error_code DataAggregator::parseAggregatedLBREntry() {
     }
 
     using SSI = StringSwitch<int>;
-    AddrNum = SSI(Str).Case("T", 3).Case("S", 1).Case("E", 0).Default(2);
+    AddrNum = SSI(Str).Cases("T", "R", 3).Case("S", 1).Case("E", 0).Default(2);
     CounterNum = SSI(Str).Case("B", 2).Case("E", 0).Default(1);
   }
 
@@ -1314,8 +1316,13 @@ std::error_code DataAggregator::parseAggregatedLBREntry() {
   }
 
   /// For legacy branch type, mark Trace To to differentite from a full trace.
-  if (Type == BRANCH) {
+  if (Type == BRANCH)
     Addr[2] = Location(Trace::BR_ONLY);
+
+  if (Type == RETURN) {
+    if (!Addr[0]->Offset)
+      Addr[0]->Offset = Trace::BR_EXTERNAL_RETURN;
+    Returns.emplace(Addr[0]->Offset);
   }
 
   /// Record a trace.

bolt/test/X86/callcont-fallthru.s

@@ -10,6 +10,8 @@
 # RUN: link_fdata %s %t %t.pa-ret PREAGG-RET
 # Trace from an external location to a landing pad/entry point call continuation
 # RUN: link_fdata %s %t %t.pa-ext PREAGG-EXT
+# Return trace to a landing pad/entry point call continuation
+# RUN: link_fdata %s %t %t.pa-pret PREAGG-PRET
 # RUN-DISABLED: link_fdata %s %t %t.pa-plt PREAGG-PLT
 
 # RUN: llvm-strip --strip-unneeded %t -o %t.strip
@@ -38,6 +40,15 @@
 # RUN: llvm-bolt %t.strip --pa -p %t.pa-ext -o %t.out \
 # RUN:   --print-cfg --print-only=main | FileCheck %s --check-prefix=CHECK-SKIP
 
+## Check pre-aggregated return traces from external location attach call
+## continuation fallthrough count to secondary entry point (unstripped)
+# RUN: llvm-bolt %t --pa -p %t.pa-pret -o %t.out \
+# RUN:   --print-cfg --print-only=main | FileCheck %s --check-prefix=CHECK-ATTACH
+## Check pre-aggregated return traces from external location attach call
+## continuation fallthrough count to landing pad (stripped, landing pad)
+# RUN: llvm-bolt %t.strip --pa -p %t.pa-pret -o %t.out \
+# RUN:   --print-cfg --print-only=main | FileCheck %s --check-prefix=CHECK-ATTACH
+
 ## Check pre-aggregated traces don't report zero-sized PLT fall-through as
 ## invalid trace
 # RUN-DISABLED: llvm-bolt %t.strip --pa -p %t.pa-plt -o %t.out | FileCheck %s \
@@ -92,6 +103,8 @@ Ltmp4_br:
 # PREAGG-RET: T #Lfoo_ret# #Ltmp3# #Ltmp3_br# 1
 ## Target is a secondary entry point (unstripped) or a landing pad (stripped)
 # PREAGG-EXT: T X:0 #Ltmp3# #Ltmp3_br# 1
+## Pre-aggregated return trace
+# PREAGG-PRET: R X:0 #Ltmp3# #Ltmp3_br# 1
 
 # CHECK-ATTACH:      callq foo
 # CHECK-ATTACH-NEXT: count: 1

bolt/test/link_fdata.py

@@ -36,9 +36,9 @@
 fdata_pat = re.compile(r"([01].*) (?P<mispred>\d+) (?P<exec>\d+)")
 
 # Pre-aggregated profile:
-# {T|S|E|B|F|f} <start> [<end>] [<ft_end>] <count> [<mispred_count>]
+# {T|R|S|E|B|F|f} <start> [<end>] [<ft_end>] <count> [<mispred_count>]
 # <loc>: [<id>:]<offset>
-preagg_pat = re.compile(r"(?P<type>[TSBFf]) (?P<offsets_count>.*)")
+preagg_pat = re.compile(r"(?P<type>[TRSBFf]) (?P<offsets_count>.*)")
 
 # No-LBR profile:
 # <is symbol?> <closest elf symbol or DSO name> <relative address> <count>