From c9f71e7ca60860344eea2256deb7d1624db05a59 Mon Sep 17 00:00:00 2001
From: Xinliang David Li <davidxl@google.com>
Date: Thu, 30 Nov 2017 19:16:25 +0000
Subject: [PATCH] [PGO] Skip counter promotion for infinite loops

Differential Revision: http://reviews.llvm.org/D40662

llvm-svn: 319462
---
 .../Instrumentation/InstrProfiling.cpp        |  3 +++
 test/Transforms/PGOProfile/infinite_loop.ll   | 21 +++++++++++++++++++
 2 files changed, 24 insertions(+)
 create mode 100644 test/Transforms/PGOProfile/infinite_loop.ll

diff --git a/lib/Transforms/Instrumentation/InstrProfiling.cpp b/lib/Transforms/Instrumentation/InstrProfiling.cpp
index db8fa897794..787afc32dfb 100644
--- a/lib/Transforms/Instrumentation/InstrProfiling.cpp
+++ b/lib/Transforms/Instrumentation/InstrProfiling.cpp
@@ -245,6 +245,9 @@ public:
   }
 
   bool run(int64_t *NumPromoted) {
+    // Skip 'infinite' loops:
+    if (ExitBlocks.size() == 0)
+      return false;
     unsigned MaxProm = getMaxNumOfPromotionsInLoop(&L);
     if (MaxProm == 0)
       return false;
diff --git a/test/Transforms/PGOProfile/infinite_loop.ll b/test/Transforms/PGOProfile/infinite_loop.ll
new file mode 100644
index 00000000000..68e9873f092
--- /dev/null
+++ b/test/Transforms/PGOProfile/infinite_loop.ll
@@ -0,0 +1,21 @@
+; RUN: opt < %s -instrprof -S -o - -do-counter-promotion=1  | FileCheck %s
+; CHECK: store
+
+@__profn_foo = private constant [3 x i8] c"foo"
+
+define void @foo() {
+entry:
+  br label %while.body
+
+  while.body:                                       ; preds = %entry, %while.body
+    call void @llvm.instrprof.increment(i8* getelementptr inbounds ([3 x i8], [3 x i8]* @__profn_foo, i32 0, i32 0), i64 14813359968, i32 1, i32 0)
+    call void (...) @bar() #2
+    br label %while.body
+}
+
+declare void @bar(...)
+
+declare void @llvm.instrprof.increment(i8*, i64, i32, i32) #0
+
+attributes #0 = { nounwind }
+