[llvm] [LLT] mark the CFI jumptable naked on Windows (PR #170371)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-transforms

Author: Mircea Trofin (mtrofin)

<details>
<summary>Changes</summary>

We were not marking the `.cfi.jumptable`​ functions as `naked`​ on windows. The referenced bug (https://llvm.org/bugs/show_bug.cgi?id=28641#c3) appears to be fixed:

```bash
build/bin/opt -S -passes=lowertypetests -mtriple=i686-pc-win32 llvm/test/Transforms/LowerTypeTests/function.ll | build/bin/llc -O0
```

```
L_.cfi.jumptable:                       # @.cfi.jumptable
# %bb.0:                                # %entry
        #APP
        jmp     _f.cfi@<!-- -->PLT
        int3
        int3
        int3

        #NO_APP
        #APP
        jmp     _g.cfi@<!-- -->PLT
        int3
        int3
        int3

        #NO_APP
                                        # -- End function
        .section        .rdata,"dr"
        .p2align        4, 0x0                          # @<!-- -->0

```

Not seeing the spilled registers described in the bug anymore, no assertions are raised either.

---
Full diff: https://github.com/llvm/llvm-project/pull/170371.diff


2 Files Affected:

- (modified) llvm/lib/Transforms/IPO/LowerTypeTests.cpp (+1-6) 
- (modified) llvm/test/Transforms/LowerTypeTests/function.ll (+1-1) 


``````````diff
diff --git a/llvm/lib/Transforms/IPO/LowerTypeTests.cpp b/llvm/lib/Transforms/IPO/LowerTypeTests.cpp
index fa35eef2c00f5..f7aeda95e41b3 100644
--- a/llvm/lib/Transforms/IPO/LowerTypeTests.cpp
+++ b/llvm/lib/Transforms/IPO/LowerTypeTests.cpp
@@ -1554,12 +1554,7 @@ void LowerTypeTestsModule::createJumpTable(
 
   // Align the whole table by entry size.
   F->setAlignment(Align(getJumpTableEntrySize(JumpTableArch)));
-  // Skip prologue.
-  // Disabled on win32 due to https://llvm.org/bugs/show_bug.cgi?id=28641#c3.
-  // Luckily, this function does not get any prologue even without the
-  // attribute.
-  if (OS != Triple::Win32)
-    F->addFnAttr(Attribute::Naked);
+  F->addFnAttr(Attribute::Naked);
   if (JumpTableArch == Triple::arm)
     F->addFnAttr("target-features", "-thumb-mode");
   if (JumpTableArch == Triple::thumb) {
diff --git a/llvm/test/Transforms/LowerTypeTests/function.ll b/llvm/test/Transforms/LowerTypeTests/function.ll
index ab3cfb6acccf8..e654da656362f 100644
--- a/llvm/test/Transforms/LowerTypeTests/function.ll
+++ b/llvm/test/Transforms/LowerTypeTests/function.ll
@@ -115,7 +115,7 @@ define i1 @foo(ptr %p) {
 ; NATIVE-SAME: "s"(ptr @g.cfi)
 
 ; X86-LINUX: attributes #[[ATTR]] = { naked nocf_check noinline }
-; X86-WIN32: attributes #[[ATTR]] = { nocf_check noinline }
+; X86-WIN32: attributes #[[ATTR]] = { naked nocf_check noinline }
 ; ARM: attributes #[[ATTR]] = { naked noinline
 ; THUMB: attributes #[[ATTR]] = { naked noinline "target-cpu"="cortex-a8" "target-features"="+thumb-mode" }
 ; THUMBV6M: attributes #[[ATTR]] = { naked noinline "target-features"="+thumb-mode" }

``````````

</details>


https://github.com/llvm/llvm-project/pull/170371