[LTT] Don't attempt to lower type tests used only by assumes

Type tests used only by assumes were original for devirtualization, but
are meant to be kept through the first invocation of LTT so that they
can be used for additional optimization. In the regular LTO case where
the IR is analyzed we may find a resolution for the type test and end up
rewriting the associated vtable global, which can have implications on
section splitting. Simply ignore these type tests.

Fixes PR48245.

Differential Revision: https://reviews.llvm.org/D96083

diff --git a/llvm/lib/Transforms/IPO/LowerTypeTests.cpp b/llvm/lib/Transforms/IPO/LowerTypeTests.cpp
index 8bd3036..adbf6e5 100644 (file)
--- a/llvm/lib/Transforms/IPO/LowerTypeTests.cpp
+++ b/llvm/lib/Transforms/IPO/LowerTypeTests.cpp
@@ -2058,6 +2058,24 @@ bool LowerTypeTestsModule::lower() {
   if (TypeTestFunc) {
     for (const Use &U : TypeTestFunc->uses()) {
       auto CI = cast<CallInst>(U.getUser());
+      // If this type test is only used by llvm.assume instructions, it
+      // was used for whole program devirtualization, and is being kept
+      // for use by other optimization passes. We do not need or want to
+      // lower it here. We also don't want to rewrite any associated globals
+      // unnecessarily. These will be removed by a subsequent LTT invocation
+      // with the DropTypeTests flag set.
+      bool OnlyAssumeUses = !CI->use_empty();
+      for (auto CIU = CI->use_begin(), CIUE = CI->use_end(); CIU != CIUE;) {
+        if (auto *AssumeCI = dyn_cast<CallInst>((*CIU++).getUser())) {
+          Function *F = AssumeCI->getCalledFunction();
+          if (F && F->getIntrinsicID() == Intrinsic::assume)
+            continue;
+        }
+        OnlyAssumeUses = false;
+        break;
+      }
+      if (OnlyAssumeUses)
+        continue;
 
       auto TypeIdMDVal = dyn_cast<MetadataAsValue>(CI->getArgOperand(1));
       if (!TypeIdMDVal)

diff --git a/llvm/test/Transforms/LowerTypeTests/pr48245.ll b/llvm/test/Transforms/LowerTypeTests/pr48245.ll
new file mode 100644 (file)
index 0000000..592ecee
--- /dev/null
+++ b/llvm/test/Transforms/LowerTypeTests/pr48245.ll
@@ -0,0 +1,48 @@
+; Test to ensure type tests that are only used in assumes are ignored by
+; LowerTypeTests (in the normal pass sequence they will be stripped out
+; by a subsequent special LTT invocation).
+
+; RUN: opt -S -passes=lowertypetests < %s | FileCheck %s
+
+; ModuleID = 'pr48245.o'
+source_filename = "pr48245.cpp"
+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"
+
+%struct.Foo = type { i32 (...)** }
+
+; Check that the vtable was not turned into an alias to a rewritten private
+; global.
+; CHECK: @_ZTV3Foo = dso_local unnamed_addr constant
+@_ZTV3Foo = dso_local unnamed_addr constant { [4 x i8*] } { [4 x i8*] [i8* null, i8* bitcast ({ i8*, i8* }* @_ZTI3Foo to i8*), i8* bitcast (i32 (%struct.Foo*)* @_ZN3Foo2f1Ev to i8*), i8* bitcast (i32 (%struct.Foo*)* @_ZN3Foo2f2Ev to i8*)] }, align 8, !type !0, !type !1, !type !2
+
+@_ZTVN10__cxxabiv117__class_type_infoE = external dso_local global i8*
+@_ZTS3Foo = dso_local constant [5 x i8] c"3Foo\00", align 1
+@_ZTI3Foo = dso_local constant { i8*, i8* } { i8* bitcast (i8** getelementptr inbounds (i8*, i8** @_ZTVN10__cxxabiv117__class_type_infoE, i64 2) to i8*), i8* getelementptr inbounds ([5 x i8], [5 x i8]* @_ZTS3Foo, i32 0, i32 0) }, align 8
+@b = dso_local local_unnamed_addr global %struct.Foo* null, align 8
+
+define dso_local i32 @main() local_unnamed_addr {
+entry:
+  %0 = load %struct.Foo*, %struct.Foo** @b, align 8
+  %1 = bitcast %struct.Foo* %0 to i32 (%struct.Foo*)***
+  %vtable.i = load i32 (%struct.Foo*)**, i32 (%struct.Foo*)*** %1, align 8
+  %2 = bitcast i32 (%struct.Foo*)** %vtable.i to i8*
+
+  ; Check that the type test was not lowered.
+  ; CHECK: tail call i1 @llvm.type.test
+  %3 = tail call i1 @llvm.type.test(i8* %2, metadata !"_ZTS3Foo")
+
+  tail call void @llvm.assume(i1 %3)
+  %4 = load i32 (%struct.Foo*)*, i32 (%struct.Foo*)** %vtable.i, align 8
+  %call.i = tail call i32 %4(%struct.Foo* nonnull dereferenceable(8) %0)
+  ret i32 %call.i
+}
+
+declare i1 @llvm.type.test(i8*, metadata)
+declare void @llvm.assume(i1 noundef)
+declare dso_local i32 @_ZN3Foo2f1Ev(%struct.Foo* nocapture nonnull readnone dereferenceable(8) %this) unnamed_addr
+declare dso_local i32 @_ZN3Foo2f2Ev(%struct.Foo* nocapture nonnull readnone dereferenceable(8) %this) unnamed_addr
+
+!0 = !{i64 16, !"_ZTS3Foo"}
+!1 = !{i64 16, !"_ZTSM3FooFivE.virtual"}
+!2 = !{i64 24, !"_ZTSM3FooFivE.virtual"}