[clang] Revert "[CodeGen] Emit vtable assumptions without requiring -fstrict-vtable-pointers" (PR #91900)

[via cfe-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang

Author: AtariDreams (AtariDreams)

<details>
<summary>Changes</summary>

This was supposed to be a temporary measure, but unfortunately as things tend to go in software development, temporary measures become permanent.

In the 9 years since then, we have greatly improved the way InstCombine works with assumes.

So, let's not make assumption loads require -fstrict-vtable-pointers.

---
Full diff: https://github.com/llvm/llvm-project/pull/91900.diff


2 Files Affected:

- (modified) clang/lib/CodeGen/CGClass.cpp (+1-4) 
- (modified) clang/test/CodeGenCXX/vtable-assume-load.cpp (+2-3) 


``````````diff
diff --git a/clang/lib/CodeGen/CGClass.cpp b/clang/lib/CodeGen/CGClass.cpp
index b3077292f4a20..70f57ff8688f7 100644
--- a/clang/lib/CodeGen/CGClass.cpp
+++ b/clang/lib/CodeGen/CGClass.cpp
@@ -2258,12 +2258,9 @@ void CodeGenFunction::EmitCXXConstructorCall(const CXXConstructorDecl *D,
   // FIXME: If vtable is used by ctor/dtor, or if vtable is external and we are
   // sure that definition of vtable is not hidden,
   // then we are always safe to refer to it.
-  // FIXME: It looks like InstCombine is very inefficient on dealing with
-  // assumes. Make assumption loads require -fstrict-vtable-pointers temporarily.
   if (CGM.getCodeGenOpts().OptimizationLevel > 0 &&
       ClassDecl->isDynamicClass() && Type != Ctor_Base &&
-      CGM.getCXXABI().canSpeculativelyEmitVTable(ClassDecl) &&
-      CGM.getCodeGenOpts().StrictVTablePointers)
+      CGM.getCXXABI().canSpeculativelyEmitVTable(ClassDecl))
     EmitVTableAssumptionLoads(ClassDecl, This);
 }
 
diff --git a/clang/test/CodeGenCXX/vtable-assume-load.cpp b/clang/test/CodeGenCXX/vtable-assume-load.cpp
index 6ce07d0db1b15..c48fc71ccea87 100644
--- a/clang/test/CodeGenCXX/vtable-assume-load.cpp
+++ b/clang/test/CodeGenCXX/vtable-assume-load.cpp
@@ -1,6 +1,5 @@
-// RUN: %clang_cc1 %s -triple x86_64-apple-darwin10 -emit-llvm -o %t.ll -O1 -disable-llvm-passes -fms-extensions -fstrict-vtable-pointers
-// RUN: %clang_cc1 %s -triple i686-pc-win32 -emit-llvm -o %t.ms.ll -O1 -disable-llvm-passes -fms-extensions -fstrict-vtable-pointers
-// FIXME: Assume load should not require -fstrict-vtable-pointers
+// RUN: %clang_cc1 %s -triple x86_64-apple-darwin10 -emit-llvm -o %t.ll -O1 -disable-llvm-passes -fms-extensions
+// RUN: %clang_cc1 %s -triple i686-pc-win32 -emit-llvm -o %t.ms.ll -O1 -disable-llvm-passes -fms-extensions
 
 // RUN: FileCheck --check-prefix=CHECK1 --input-file=%t.ll %s
 // RUN: FileCheck --check-prefix=CHECK2 --input-file=%t.ll %s

``````````

</details>


https://github.com/llvm/llvm-project/pull/91900