[clang] [llvm] [clang backend] In AArch64's DataLayout, specify a minimum function alignment of 4. (PR #90702)

[Doug Wyatt via llvm-commits]

https://github.com/dougsonos created https://github.com/llvm/llvm-project/pull/90702

This addresses an issue where the explicit alignment of 2 (for C++ ABI reasons) was being propagated to the back end and causing under-aligned functions (in special sections). (#90358)

This is an alternate approach suggested by @efriedma-quic in PR #90415.

(There are a few failing tests. One I looked at was checking for the explicit alignment of 2, which no longer appears in AArch64 due to this change.)


>From 4c312af7af5d0e419269c5b2304b0f898363bb85 Mon Sep 17 00:00:00 2001
From: Doug Wyatt <dwyatt at apple.com>
Date: Tue, 30 Apr 2024 21:43:16 -0700
Subject: [PATCH] In AArch64's DataLayout, specify a minimum function alignment
 of 4. This addresses an issue where the explicit alignment of 2 (for C++ ABI
 reasons) was being propagated to the back end and causing under-aligned
 functions (in special sections). (#90358)

---
 clang/lib/Basic/Targets/AArch64.cpp              | 12 ++++++------
 llvm/lib/IR/AutoUpgrade.cpp                      |  8 ++++++++
 llvm/lib/Target/AArch64/AArch64TargetMachine.cpp |  8 ++++----
 3 files changed, 18 insertions(+), 10 deletions(-)

diff --git a/clang/lib/Basic/Targets/AArch64.cpp b/clang/lib/Basic/Targets/AArch64.cpp
index c8d243a8fb7aea..a5dd803f636b90 100644
--- a/clang/lib/Basic/Targets/AArch64.cpp
+++ b/clang/lib/Basic/Targets/AArch64.cpp
@@ -1480,11 +1480,11 @@ AArch64leTargetInfo::AArch64leTargetInfo(const llvm::Triple &Triple,
 void AArch64leTargetInfo::setDataLayout() {
   if (getTriple().isOSBinFormatMachO()) {
     if(getTriple().isArch32Bit())
-      resetDataLayout("e-m:o-p:32:32-i64:64-i128:128-n32:64-S128", "_");
+      resetDataLayout("e-m:o-p:32:32-Fn32-i64:64-i128:128-n32:64-S128", "_");
     else
-      resetDataLayout("e-m:o-i64:64-i128:128-n32:64-S128", "_");
+      resetDataLayout("e-m:o-Fn32-i64:64-i128:128-n32:64-S128", "_");
   } else
-    resetDataLayout("e-m:e-i8:8:32-i16:16:32-i64:64-i128:128-n32:64-S128");
+    resetDataLayout("e-m:e-Fn32-i8:8:32-i16:16:32-i64:64-i128:128-n32:64-S128");
 }
 
 void AArch64leTargetInfo::getTargetDefines(const LangOptions &Opts,
@@ -1507,7 +1507,7 @@ void AArch64beTargetInfo::getTargetDefines(const LangOptions &Opts,
 
 void AArch64beTargetInfo::setDataLayout() {
   assert(!getTriple().isOSBinFormatMachO());
-  resetDataLayout("E-m:e-i8:8:32-i16:16:32-i64:64-i128:128-n32:64-S128");
+  resetDataLayout("E-m:e-Fn32-i8:8:32-i16:16:32-i64:64-i128:128-n32:64-S128");
 }
 
 WindowsARM64TargetInfo::WindowsARM64TargetInfo(const llvm::Triple &Triple,
@@ -1530,8 +1530,8 @@ WindowsARM64TargetInfo::WindowsARM64TargetInfo(const llvm::Triple &Triple,
 
 void WindowsARM64TargetInfo::setDataLayout() {
   resetDataLayout(Triple.isOSBinFormatMachO()
-                      ? "e-m:o-i64:64-i128:128-n32:64-S128"
-                      : "e-m:w-p:64:64-i32:32-i64:64-i128:128-n32:64-S128",
+                      ? "e-m:o-Fn32-i64:64-i128:128-n32:64-S128"
+                      : "e-m:w-p:64:64-Fn32-i32:32-i64:64-i128:128-n32:64-S128",
                   Triple.isOSBinFormatMachO() ? "_" : "");
 }
 
diff --git a/llvm/lib/IR/AutoUpgrade.cpp b/llvm/lib/IR/AutoUpgrade.cpp
index 634b2dd5119e8d..eed946dc36580e 100644
--- a/llvm/lib/IR/AutoUpgrade.cpp
+++ b/llvm/lib/IR/AutoUpgrade.cpp
@@ -5387,6 +5387,14 @@ std::string llvm::UpgradeDataLayoutString(StringRef DL, StringRef TT) {
     return Res;
   }
 
+  // AArch64 data layout upgrades.
+  if (T.isAArch64()) {
+    // Add "-Fn32"
+    if (!DL.contains("-Fn32"))
+      Res.append("-Fn32");
+    return Res;
+  }
+
   if (!T.isX86())
     return Res;
 
diff --git a/llvm/lib/Target/AArch64/AArch64TargetMachine.cpp b/llvm/lib/Target/AArch64/AArch64TargetMachine.cpp
index 7ef78cbba352a5..4ff5fb94162a93 100644
--- a/llvm/lib/Target/AArch64/AArch64TargetMachine.cpp
+++ b/llvm/lib/Target/AArch64/AArch64TargetMachine.cpp
@@ -275,15 +275,15 @@ static std::string computeDataLayout(const Triple &TT,
                                      bool LittleEndian) {
   if (TT.isOSBinFormatMachO()) {
     if (TT.getArch() == Triple::aarch64_32)
-      return "e-m:o-p:32:32-i64:64-i128:128-n32:64-S128";
-    return "e-m:o-i64:64-i128:128-n32:64-S128";
+      return "e-m:o-p:32:32-Fn32-i64:64-i128:128-n32:64-S128";
+    return "e-m:o-Fn32-i64:64-i128:128-n32:64-S128";
   }
   if (TT.isOSBinFormatCOFF())
-    return "e-m:w-p:64:64-i32:32-i64:64-i128:128-n32:64-S128";
+    return "e-m:w-p:64:64-Fn32-i32:32-i64:64-i128:128-n32:64-S128";
   std::string Endian = LittleEndian ? "e" : "E";
   std::string Ptr32 = TT.getEnvironment() == Triple::GNUILP32 ? "-p:32:32" : "";
   return Endian + "-m:e" + Ptr32 +
-         "-i8:8:32-i16:16:32-i64:64-i128:128-n32:64-S128";
+         "-Fn32-i8:8:32-i16:16:32-i64:64-i128:128-n32:64-S128";
 }
 
 static StringRef computeDefaultCPU(const Triple &TT, StringRef CPU) {