[llvm] [AArch64] fall back to SDAG for instructions with emulated TLS variables (PR #129215)

[Sebastian Schaller via llvm-commits]

https://github.com/sschaller updated https://github.com/llvm/llvm-project/pull/129215

>From d07d6b516e0fd2c8bc0f35afe61d082a6634a6a5 Mon Sep 17 00:00:00 2001
From: "Schaller, Sebastian" <sebastian.schaller at dentsplysirona.com>
Date: Wed, 26 Feb 2025 10:12:50 +0100
Subject: [PATCH] [AArch64] Fall back to SDAG for instructions with emulated
 TLS variables

---
 .../GISel/AArch64InstructionSelector.cpp      |  6 +++-
 .../AArch64/GlobalISel/emutls-fallback.ll     | 29 +++++++++++++++++++
 2 files changed, 34 insertions(+), 1 deletion(-)
 create mode 100644 llvm/test/CodeGen/AArch64/GlobalISel/emutls-fallback.ll

diff --git a/llvm/lib/Target/AArch64/GISel/AArch64InstructionSelector.cpp b/llvm/lib/Target/AArch64/GISel/AArch64InstructionSelector.cpp
index 467094e9befef..1cc7480e44eae 100644
--- a/llvm/lib/Target/AArch64/GISel/AArch64InstructionSelector.cpp
+++ b/llvm/lib/Target/AArch64/GISel/AArch64InstructionSelector.cpp
@@ -2960,8 +2960,12 @@ bool AArch64InstructionSelector::select(MachineInstr &I) {
       assert(OpFlags == AArch64II::MO_GOT);
     } else {
       GV = I.getOperand(1).getGlobal();
-      if (GV->isThreadLocal())
+      if (GV->isThreadLocal()) {
+        // We don't support instructions with emulated TLS variables yet
+        if (TM.useEmulatedTLS())
+          return false;
         return selectTLSGlobalValue(I, MRI);
+      }
       OpFlags = STI.ClassifyGlobalReference(GV, TM);
     }
 
diff --git a/llvm/test/CodeGen/AArch64/GlobalISel/emutls-fallback.ll b/llvm/test/CodeGen/AArch64/GlobalISel/emutls-fallback.ll
new file mode 100644
index 0000000000000..e90b3e2d05afa
--- /dev/null
+++ b/llvm/test/CodeGen/AArch64/GlobalISel/emutls-fallback.ll
@@ -0,0 +1,29 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py UTC_ARGS: --version 5
+; RUN: llc -emulated-tls -mtriple aarch64-apple-darwin -global-isel -global-isel-abort=2 %s -o - 2>&1 | FileCheck %s
+
+; This file checks that the fallback path for instructions with emulated TLS variables to selection dag works.
+
+; CHECK:        warning: Instruction selection used fallback path for main
+
+ at x = thread_local global i32 42, align 4
+
+define i32 @main(i32 %argc, ptr %argv) {
+; CHECK-LABEL: main:
+; CHECK:       ; %bb.0: ; %entry
+; CHECK-NEXT:    stp x29, x30, [sp, #-16]! ; 16-byte Folded Spill
+; CHECK-NEXT:    .cfi_def_cfa_offset 16
+; CHECK-NEXT:    .cfi_offset w30, -8
+; CHECK-NEXT:    .cfi_offset w29, -16
+; CHECK-NEXT:  Lloh0:
+; CHECK-NEXT:    adrp x0, ___emutls_v.x at PAGE
+; CHECK-NEXT:  Lloh1:
+; CHECK-NEXT:    add x0, x0, ___emutls_v.x at PAGEOFF
+; CHECK-NEXT:    bl ___emutls_get_address
+; CHECK-NEXT:    ldr w0, [x0]
+; CHECK-NEXT:    ldp x29, x30, [sp], #16 ; 16-byte Folded Reload
+; CHECK-NEXT:    ret
+; CHECK-NEXT:    .loh AdrpAdd Lloh0, Lloh1
+entry:
+  %0 = load i32, ptr @x, align 4
+  ret i32 %0
+}