[InitUndef] handleSubReg should skip artificial subregs. #116248
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When enabling subreg liveness tracking for AArch64, this pass fails because it tries to get the register class for the artificial subreg `sub_32_hi` of a 64-bit GPR. It tries to create an INIT_UNDEF instruction for the top 32-bits of the 64-bit GPR, which are not directly addressable, so getSubRegisterClass() returns a nullptr, crashing this pass. It should instead just avoid trying to create the INIT_UNDEF instruction.
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@llvm/pr-subscribers-backend-aarch64 Author: Sander de Smalen (sdesmalen-arm) ChangesWhen enabling subreg liveness tracking for AArch64, this pass fails because it tries to get the register class for the artificial subreg It should instead just avoid trying to create the INIT_UNDEF instruction. Full diff: https://github.com/llvm/llvm-project/pull/116248.diff 2 Files Affected:
diff --git a/llvm/lib/CodeGen/InitUndef.cpp b/llvm/lib/CodeGen/InitUndef.cpp
index d4ac131a32a959..7b00611b63b7bf 100644
--- a/llvm/lib/CodeGen/InitUndef.cpp
+++ b/llvm/lib/CodeGen/InitUndef.cpp
@@ -164,6 +164,15 @@ bool InitUndef::handleSubReg(MachineFunction &MF, MachineInstr &MI,
TRI->getCoveringSubRegIndexes(*MRI, TargetRegClass, NeedDef,
SubRegIndexNeedInsert);
+ // It's not possible to create the INIT_UNDEF when there is no register
+ // class associated for the subreg. This may happen for artificial subregs
+ // that are not directly addressable.
+ if (any_of(SubRegIndexNeedInsert,
+ [&TRI = TRI, &TargetRegClass](unsigned ind) -> bool {
+ return !TRI->getSubRegisterClass(TargetRegClass, ind);
+ }))
+ continue;
+
Register LatestReg = Reg;
for (auto ind : SubRegIndexNeedInsert) {
Changed = true;
diff --git a/llvm/test/CodeGen/AArch64/init-undef.mir b/llvm/test/CodeGen/AArch64/init-undef.mir
index 7935c09d7df5ec..c9d23006d35234 100644
--- a/llvm/test/CodeGen/AArch64/init-undef.mir
+++ b/llvm/test/CodeGen/AArch64/init-undef.mir
@@ -1,5 +1,6 @@
# NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py UTC_ARGS: --version 5
-# RUN: llc -mtriple=aarch64-- -run-pass=init-undef -o - %s | FileCheck %s
+# RUN: llc -mtriple=aarch64-- -aarch64-enable-subreg-liveness-tracking=false -run-pass=init-undef -o - %s | FileCheck %s
+# RUN: llc -mtriple=aarch64-- -aarch64-enable-subreg-liveness-tracking=true -run-pass=init-undef -o - %s | FileCheck %s
---
name: test_stxp_undef
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nikic
approved these changes
Nov 14, 2024
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Thank you for the prompt reviews! |
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✅ With the latest revision this PR passed the C/C++ code formatter. |
Co-authored-by: Nikita Popov <[email protected]>
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When enabling subreg liveness tracking for AArch64, this pass fails because it tries to get the register class for the artificial subreg
sub_32_hiof a 64-bit GPR. It tries to create an INIT_UNDEF instruction for the top 32-bits of the 64-bit GPR, which are not directly addressable, so getSubRegisterClass() returns a nullptr, crashing this pass.It should instead just avoid trying to create the INIT_UNDEF instruction.