[AArch64] fall back to SDAG for instructions with emulated TLS variables

[sschaller]

Fixes #126200
At the moment, GlobalISel is missing an implementation for emulated TLS variables.
I fixed the issue by falling back to SDAG in this case, as I currently don't have the knowledge to implement it myself.

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[llvmbot]

@llvm/pr-subscribers-llvm-globalisel

@llvm/pr-subscribers-backend-aarch64

Author: Sebastian Schaller (sschaller)

Changes

Fixes #126200
At the moment, GlobalISel is missing an implementation for emulated TLS variables.
I fixed the issue by falling back to SDAG in this case, as I currently don't have the knowledge to implement it myself.

---

Full diff: https://github.com/llvm/llvm-project/pull/129215.diff

1 Files Affected:

• (modified) llvm/lib/Target/AArch64/GISel/AArch64InstructionSelector.cpp (+5-1)

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);
     }
 

[davemgreen]

Can you add a test case? Thanks

[sschaller]

Added. I chose to make it a separate file to test the fallback itself. Feel free to suggest another location.

[davemgreen]

Thanks. Looks great, with a minor comment about the test.

LGTM

[davemgreen]

Can remove --check-prefix=CHECK as it is the default.

[sschaller]

Thanks! I made the change and squashed the commits. Could you merge for me? I don't think I have the rights to.

[davemgreen]

Thanks. LGTM

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