[ThinLTO] Disallow importing for functions with indir branch to block address

We don't allowing inlining for functions with blockaddress with uses other than strictly callbr. This is because if the blockaddress escapes the function via a global variable, inlining may lead to an invalid cross-function reference.

We check against such cases during inlining, however the check can fail for ThinLTO post-link because CFG simplification can incorrectly removes blocks based on wrong block reachability.

When we import a function with blockaddress taken in a global variable but without importing that variable, we won't go through value mapping to reflect the real address-taken-ness of the cloned blocks. For the imported clone, this leads to blocks reachable from indirect branch through global variable being incorrectly treated as unreachable and removed by SimplifyCFG.

Since inlining for such cases shouldn't be allowed in the first place, I'm marking them as ineligible for importing during pre-link to save the problem of missing address-taken-ness of imported clone as well as bad DCE and inlining.

Differential Revision: https://reviews.llvm.org/D106930

llvm/lib/Analysis/ModuleSummaryAnalysis.cpp

@@ -264,7 +264,20 @@ static void computeFunctionSummary(
   std::vector<const Instruction *> NonVolatileStores;
 
   bool HasInlineAsmMaybeReferencingInternal = false;
-  for (const BasicBlock &BB : F)
+  bool HasIndirBranchToBlockAddress = false;
+  for (const BasicBlock &BB : F) {
+    // We don't allow inlining of function with indirect branch to blockaddress.
+    // If the blockaddress escapes the function, e.g., via a global variable,
+    // inlining may lead to an invalid cross-function reference. So we shouldn't
+    // import such function either.
+    if (BB.hasAddressTaken()) {
+      for (User *U : BlockAddress::get(const_cast<BasicBlock *>(&BB))->users())
+        if (!isa<CallBrInst>(*U)) {
+          HasIndirBranchToBlockAddress = true;
+          break;
+        }
+    }
+
     for (const Instruction &I : BB) {
       if (isa<DbgInfoIntrinsic>(I))
         continue;
@@ -386,6 +399,7 @@ static void computeFunctionSummary(
               .updateHotness(getHotness(Candidate.Count, PSI));
       }
     }
+  }
   Index.addBlockCount(F.size());
 
   std::vector<ValueInfo> Refs;
@@ -452,8 +466,9 @@ static void computeFunctionSummary(
             : CalleeInfo::HotnessType::Critical);
 
   bool NonRenamableLocal = isNonRenamableLocal(F);
-  bool NotEligibleForImport =
-      NonRenamableLocal || HasInlineAsmMaybeReferencingInternal;
+  bool NotEligibleForImport = NonRenamableLocal ||
+                              HasInlineAsmMaybeReferencingInternal ||
+                              HasIndirBranchToBlockAddress;
   GlobalValueSummary::GVFlags Flags(
       F.getLinkage(), F.getVisibility(), NotEligibleForImport,
       /* Live = */ false, F.isDSOLocal(),

llvm/test/ThinLTO/X86/Inputs/globals-import-blockaddr.ll

@@ -1,10 +1,15 @@
 target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
 target triple = "x86_64-unknown-linux-gnu"
 
-@label_addr = internal constant [1 x i8*] [i8* blockaddress(@foo, %lb)], align 8
+@label_addr = internal constant [1 x i8*] [i8* blockaddress(@bar, %lb)], align 8
 
 ; Function Attrs: noinline norecurse nounwind optnone uwtable
 define dso_local [1 x i8*]* @foo() {
+  ret [1 x i8*]* @label_addr
+}
+
+; Function Attrs: noinline norecurse nounwind optnone uwtable
+define dso_local [1 x i8*]* @bar() {
   br label %lb
 
 lb:

llvm/test/ThinLTO/X86/globals-import-blockaddr.ll

@@ -1,18 +1,26 @@
 ; RUN: opt -module-summary %s -o %t1.bc
 ; RUN: opt -module-summary %p/Inputs/globals-import-blockaddr.ll -o %t2.bc
-; RUN: llvm-lto2 run -save-temps %t1.bc -r=%t1.bc,foo,l -r=%t1.bc,main,pl %t2.bc -r=%t2.bc,foo,pl -o %t3
+; RUN: llvm-lto2 run -save-temps %t1.bc -r=%t1.bc,foo,l -r=%t1.bc,bar,l -r=%t1.bc,main,pl %t2.bc -r=%t2.bc,foo,pl -r=%t2.bc,bar,pl -o %t3
 ; RUN: llvm-dis %t3.1.3.import.bc -o - | FileCheck %s
 
 ; Verify that we haven't imported GV containing blockaddress
 ; CHECK: @label_addr.llvm.0 = external hidden constant
+; Verify that bar is not imported since it has address-taken block that is target of indirect branch
+; CHECK: declare [1 x i8*]* @bar()
+; Verify that foo is imported
+; CHECK: available_externally [1 x i8*]* @foo
 
 target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
 target triple = "x86_64-unknown-linux-gnu"
 
 declare dso_local [1 x i8*]* @foo();
+declare dso_local [1 x i8*]* @bar();
 
 define dso_local i32 @main() {
-  %p = call [1 x i8*]* @foo()
-  %v = ptrtoint [1 x i8*]* %p to i32
-  ret i32 %v
+  %p1 = call [1 x i8*]* @foo()
+  %p2 = call [1 x i8*]* @bar()
+  %v1 = ptrtoint [1 x i8*]* %p1 to i32
+  %v2 = ptrtoint [1 x i8*]* %p2 to i32
+  %v3 = add i32 %v1, %v2
+  ret i32 %v3
 }