[CSSPGO][llvm-profgen] Ignore LBR records after interrupt transition

If we have seen an inwards transition from external code to internal code, but not a following outwards transition, the inwards transition is likely due to interrupt which is usually unpaired. Ignore current  and subsequent entries since they are likely from an unrelated pre-interrupt context.

LBR records from different interrupt context are unrelated and they should not be mixed together. Currenlty the OS does this for task-scheduling interrupt but not for all interrupts.

Reviewed By: wenlei, wlei

Differential Revision: https://reviews.llvm.org/D104276

test/tools/llvm-profgen/Inputs/cs-interrupt.perfscript

@@ -0,0 +1,16 @@
+PERF_RECORD_MMAP2 2854748/2854748: [0x400000(0x1000) @ 0 00:1d 123291722 526021]: r-xp /home/noinline-cs-noprobe.perfbin
+
+	          4005dc
+	          400634
+	          400684
+	    7f68c5788793
+ 0x4005c8/0x4005dc/P/-/-/0  0x40062f/0x4005b0/P/-/-/0  0x400645/0x4005ff/P/-/-/0  0x400637/0x400645/P/-/-/0  0x4005e9/0x400634/P/-/-/0  0x4005d7/0x4005e5/P/-/-/0  0x40062f/0x4005b0/P/-/-/0  0x400645/0x4005ff/P/-/-/0  0x400637/0x400645/P/-/-/0  0x4005e9/0x400634/P/-/-/0  0x4005d7/0x4005e5/P/-/-/0  0x40062f/0x4005b0/P/-/-/0  0x400645/0x4005ff/P/-/-/0  0x400637/0x400645/P/-/-/0  0xffffffff81c009d0/0x400634/P/-/-/0  0x40048a/0x40048e/P/-/-/0
+
+
+	          4005dc
+	          400634
+	          400684
+	    7f68c5788793
+ 0x4005c8/0x4005dc/P/-/-/0  0x40062f/0x4005b0/P/-/-/0  0x400645/0x4005ff/P/-/-/0  0x400637/0x400645/P/-/-/0  0x4005e9/0x400634/P/-/-/0  0x4005d7/0x4005e5/P/-/-/0  0x40062f/0x4005b0/P/-/-/0  0x400645/0x4005ff/P/-/-/0  0x400637/0x400645/P/-/-/0  0x4005e9/0x400634/P/-/-/0  0x4005d7/0x4005e5/P/-/-/0  0x400634/0xffffffff81c009d0/P/-/-/0 0x40062f/0x4005b0/P/-/-/0  0x400645/0x4005ff/P/-/-/0  0x400637/0x400645/P/-/-/0  0x40048a/0x40048e/P/-/-/0
+
+// Transition 0xffffffff81c009d0/0x400634 is due to interrupt. Records after it, i.e, 0x40048a/0x40048e, should be ignored to avoid bogus instruction ranges.

test/tools/llvm-profgen/cs-interrupt.test

@@ -0,0 +1,56 @@
+; RUN: llvm-profgen --format=text --perfscript=%S/Inputs/cs-interrupt.perfscript --binary=%S/Inputs/noinline-cs-noprobe.perfbin --output=%t --show-unwinder-output --profile-summary-cold-count=0 | FileCheck %s --check-prefix=CHECK-UNWINDER
+; RUN: FileCheck %s --input-file %t
+
+; CHECK:[main:1 @ foo]:88:0
+; CHECK: 2: 5
+; CHECK: 3: 5 bar:5
+; CHECK:[main:1 @ foo:3 @ bar]:74:5
+; CHECK: 0: 5
+; CHECK: 1: 5
+; CHECK: 2: 3
+; CHECK: 5: 4
+
+; CHECK-UNWINDER: Binary(noinline-cs-noprobe.perfbin)'s Range Counter:
+; CHECK-UNWINDER: main:1 @ foo
+; CHECK-UNWINDER:   (5ff, 62f): 5
+; CHECK-UNWINDER:   (634, 637): 4
+; CHECK-UNWINDER:   (645, 645): 5
+; CHECK-UNWINDER: main:1 @ foo:3 @ bar
+; CHECK-UNWINDER:   (5b0, 5c8): 2
+; CHECK-UNWINDER:   (5b0, 5d7): 3
+; CHECK-UNWINDER:   (5e5, 5e9): 4
+
+; CHECK-UNWINDER: Binary(noinline-cs-noprobe.perfbin)'s Branch Counter:
+; CHECK-UNWINDER: main:1 @ foo
+; CHECK-UNWINDER:   (62f, 5b0): 5
+; CHECK-UNWINDER:   (637, 645): 5
+; CHECK-UNWINDER:   (645, 5ff): 5
+; CHECK-UNWINDER: main:1 @ foo:3 @ bar
+; CHECK-UNWINDER:   (5c8, 5dc): 2
+; CHECK-UNWINDER:   (5d7, 5e5): 4
+; CHECK-UNWINDER:   (5e9, 634): 4
+
+
+
+; original code:
+; clang -O0 -g test.c -o a.out
+#include <stdio.h>
+
+int bar(int x, int y) {
+  if (x % 3) {
+    return x - y;
+  }
+  return x + y;
+}
+
+void foo() {
+  int s, i = 0;
+  while (i++ < 4000 * 4000)
+    if (i % 91) s = bar(i, s); else s += 30;
+  printf("sum is %d\n", s);
+}
+
+int main() {
+  foo();
+  return 0;
+}

tools/llvm-profgen/PerfReader.cpp

@@ -444,27 +444,47 @@ bool PerfReader::extractLBRStack(TraceStream &TraceIt,
 
     bool SrcIsInternal = Binary->addressIsCode(Src);
     bool DstIsInternal = Binary->addressIsCode(Dst);
+    bool IsExternal = !SrcIsInternal && !DstIsInternal;
+    bool IsIncoming = !SrcIsInternal && DstIsInternal;
+    bool IsOutgoing = SrcIsInternal && !DstIsInternal;
     bool IsArtificial = false;
+
     // Ignore branches outside the current binary.
-    if (!SrcIsInternal && !DstIsInternal)
+    if (IsExternal)
       continue;
-    if (!SrcIsInternal && DstIsInternal) {
+
-      // For transition from external code (such as dynamic libraries) to
+    if (IsOutgoing) {
-      // the current binary, keep track of the branch target which will be
+      if (!PrevTrDst) {
-      // grouped with the Source of the last transition from the current
+        // This is unpaired outgoing jump which is likely due to interrupt or
-      // binary.
+        // incomplete LBR trace. Ignore current and subsequent entries since
-      PrevTrDst = Dst;
+        // they are likely in different contexts.
-      continue;
+        break;
-    }
+      }
-    if (SrcIsInternal && !DstIsInternal) {
       // For transition to external code, group the Source with the next
       // availabe transition target.
-      if (!PrevTrDst)
-        continue;
       Dst = PrevTrDst;
       PrevTrDst = 0;
       IsArtificial = true;
+    } else {
+      if (PrevTrDst) {
+        // If we have seen an incoming transition from external code to internal
+        // code, but not a following outgoing transition, the incoming
+        // transition is likely due to interrupt which is usually unpaired.
+        // Ignore current and subsequent entries since they are likely in
+        // different contexts.
+        break;
+      }
+
+      if (IsIncoming) {
+        // For transition from external code (such as dynamic libraries) to
+        // the current binary, keep track of the branch target which will be
+        // grouped with the Source of the last transition from the current
+        // binary.
+        PrevTrDst = Dst;
+        continue;
+      }
     }
+
     // TODO: filter out buggy duplicate branches on Skylake
 
     LBRStack.emplace_back(LBREntry(Src, Dst, IsArtificial));