Regard unreachable function as a possible devirtualizable target
patch.cherry: true
patch.metadata.original_sha: 830c0d493aee2f86a4e8e0e6711df93f53399364
patch.platforms: chromiumos
patch.version_range.from: 547379
patch.version_range.until: 555655
BUG=b:362469536
TEST=built llvm with this, then chrome. chrome no longer incorrectly
TEST=contains the direct call in the referenced bug
Change-Id: I1e34222f1c9115da03ae5e60b93f6b8f859e6807
diff --git a/llvm/lib/Transforms/IPO/WholeProgramDevirt.cpp b/llvm/lib/Transforms/IPO/WholeProgramDevirt.cpp
index 19bc841..9c56e38 100644
--- a/llvm/lib/Transforms/IPO/WholeProgramDevirt.cpp
+++ b/llvm/lib/Transforms/IPO/WholeProgramDevirt.cpp
@@ -168,6 +168,18 @@
cl::desc("Prevent function(s) from being devirtualized"),
cl::Hidden, cl::CommaSeparated);
+/// A function is unreachable if its entry block ends with 'unreachable' IR
+/// instruction. In some cases, the program intends to run such functions and
+/// terminate, for instance, a unit test may run a death test. A non-test
+/// program might (or allowed to) invoke such functions to report failures
+/// (whether/when it's a good practice or not is a different topic). Regard
+/// unreachable function as possible devirtualize targets to keep the program
+/// behavior.
+static cl::opt<bool> WholeProgramDevirtKeepUnreachableFunction(
+ "wholeprogramdevirt-keep-unreachable-function",
+ cl::desc("Regard unreachable functions as possible devirtualize targets."),
+ cl::Hidden, cl::init(true));
+
/// Mechanism to add runtime checking of devirtualization decisions, optionally
/// trapping or falling back to indirect call on any that are not correct.
/// Trapping mode is useful for debugging undefined behavior leading to failures
@@ -376,6 +388,9 @@
// 2) All function summaries indicate it's unreachable
// 3) There is no non-function with the same GUID (which is rare)
static bool mustBeUnreachableFunction(ValueInfo TheFnVI) {
+ if (WholeProgramDevirtKeepUnreachableFunction)
+ return false;
+
if ((!TheFnVI) || TheFnVI.getSummaryList().empty()) {
// Returns false if ValueInfo is absent, or the summary list is empty
// (e.g., function declarations).
@@ -2223,6 +2238,8 @@
bool DevirtModule::mustBeUnreachableFunction(
Function *const F, ModuleSummaryIndex *ExportSummary) {
+ if (WholeProgramDevirtKeepUnreachableFunction)
+ return false;
// First, learn unreachability by analyzing function IR.
if (!F->isDeclaration()) {
// A function must be unreachable if its entry block ends with an
diff --git a/llvm/test/Transforms/WholeProgramDevirt/devirt_single_after_filtering_unreachable_function.ll b/llvm/test/Transforms/WholeProgramDevirt/devirt_single_after_filtering_unreachable_function.ll
index 457120b..599d329 100644
--- a/llvm/test/Transforms/WholeProgramDevirt/devirt_single_after_filtering_unreachable_function.ll
+++ b/llvm/test/Transforms/WholeProgramDevirt/devirt_single_after_filtering_unreachable_function.ll
@@ -1,11 +1,15 @@
+; Test that static devirtualization doesn't happen because there are two
+; devirtualizable targets. Unreachable functions are kept in the devirtualizable
+; target set by default.
+; RUN: opt -S -passes=wholeprogramdevirt -whole-program-visibility -pass-remarks=wholeprogramdevirt %s 2>&1 | FileCheck %s --implicit-check-not="single-impl"
+
; Test that regular LTO will analyze IR, detect unreachable functions and discard unreachable functions
; when finding virtual call targets.
; In this test case, the unreachable function is the virtual deleting destructor of an abstract class.
+; RUN: opt -S -passes=wholeprogramdevirt -whole-program-visibility -pass-remarks=wholeprogramdevirt -wholeprogramdevirt-keep-unreachable-function=false %s 2>&1 | FileCheck %s --check-prefix=DEVIRT
-; RUN: opt -S -passes=wholeprogramdevirt -whole-program-visibility -pass-remarks=wholeprogramdevirt %s 2>&1 | FileCheck %s
-
-; CHECK: remark: tmp.cc:21:3: single-impl: devirtualized a call to _ZN7DerivedD0Ev
-; CHECK: remark: <unknown>:0:0: devirtualized _ZN7DerivedD0Ev
+; DEVIRT: remark: tmp.cc:21:3: single-impl: devirtualized a call to _ZN7DerivedD0Ev
+; DEVIRT: remark: <unknown>:0:0: devirtualized _ZN7DerivedD0Ev
source_filename = "tmp.cc"
target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
