[ThinLTO] Record calls to aliases

Summary:
When there is a call to an alias in the same module, we were not
adding a call edge. So we could incorrectly think that the alias
was dead if it was inlined in that function, despite having a
reference imported elsewhere. This resulted in unsats at link time.

Add a call edge when the call is to an alias.

Reviewers: davide, mehdi_amini

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D25384

llvm-svn: 283664

2 files changed, 40 insertions, 1 deletions

diff --git a/llvm/lib/Analysis/ModuleSummaryAnalysis.cpp b/llvm/lib/Analysis/ModuleSummaryAnalysis.cpp
index 5a9d9a6604f..c107deb0a6e 100644
--- a/llvm/lib/Analysis/ModuleSummaryAnalysis.cpp
+++ b/llvm/lib/Analysis/ModuleSummaryAnalysis.cpp
@@ -101,15 +101,26 @@ static void computeFunctionSummary(ModuleSummaryIndex &Index, const Module &M,
       auto CS = ImmutableCallSite(&I);
       if (!CS)
         continue;
+      auto *CalledValue = CS.getCalledValue();
       auto *CalledFunction = CS.getCalledFunction();
+      // Check if this is an alias to a function. If so, get the
+      // called aliasee for the checks below.
+      if (auto *GA = dyn_cast<GlobalAlias>(CalledValue)) {
+        assert(!CalledFunction && "Expected null called function in callsite for alias");
+        CalledFunction = dyn_cast<Function>(GA->getBaseObject());
+      }
       // Check if this is a direct call to a known function.
       if (CalledFunction) {
         // Skip nameless and intrinsics.
         if (!CalledFunction->hasName() || CalledFunction->isIntrinsic())
           continue;
         auto ScaledCount = BFI ? BFI->getBlockProfileCount(&BB) : None;
+        // Use the original CalledValue, in case it was an alias. We want
+        // to record the call edge to the alias in that case. Eventually
+        // an alias summary will be created to associate the alias and
+        // aliasee.
         auto *CalleeId =
-            M.getValueSymbolTable().lookup(CalledFunction->getName());
+            M.getValueSymbolTable().lookup(CalledValue->getName());
 
         auto Hotness = ScaledCount ? getHotness(ScaledCount.getValue(), PSI)
                                    : CalleeInfo::HotnessType::Unknown;
diff --git a/llvm/test/Bitcode/thinlto-alias2.ll b/llvm/test/Bitcode/thinlto-alias2.ll
new file mode 100644
index 00000000000..d2b7f723fa4
--- /dev/null
+++ b/llvm/test/Bitcode/thinlto-alias2.ll
@@ -0,0 +1,28 @@
+; Test to check the callgraph for call to alias in module.
+; RUN: opt -module-summary %s -o %t.o
+; RUN: llvm-bcanalyzer -dump %t.o | FileCheck %s
+
+; CHECK:       <GLOBALVAL_SUMMARY_BLOCK
+; CHECK-NEXT:    <VERSION
+; CHECK-NEXT:    <PERMODULE {{.*}} op3=0 op4=[[ALIASID:[0-9]+]]/>
+; CHECK-NEXT:    <PERMODULE {{.*}} op0=[[ALIASEEID:[0-9]+]]
+; CHECK-NEXT:    <ALIAS {{.*}} op0=[[ALIASID]] {{.*}} op2=[[ALIASEEID]]/>
+; CHECK-NEXT:  </GLOBALVAL_SUMMARY_BLOCK>
+
+; ModuleID = 'thinlto-alias2.ll'
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+define i32 @main() {
+entry:
+    call void (...) @analias()
+    ret i32 0
+}
+
+@analias = alias void (...), bitcast (void ()* @aliasee to void (...)*)
+
+define void @aliasee() #0 {
+entry:
+    ret void
+}
+