[llvm] [CodeGen][NFC] Guard copy propagation in machine CSE against undefs (PR #97413)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-backend-amdgpu

Author: Vikram Hegde (vikramRH)

<details>
<summary>Changes</summary>



---
Full diff: https://github.com/llvm/llvm-project/pull/97413.diff


2 Files Affected:

- (modified) llvm/lib/CodeGen/MachineCSE.cpp (+1-1) 
- (added) llvm/test/CodeGen/AMDGPU/machine-cse-copyprop.mir (+21) 


``````````diff
diff --git a/llvm/lib/CodeGen/MachineCSE.cpp b/llvm/lib/CodeGen/MachineCSE.cpp
index 4e6101f875589..e39aae56bf116 100644
--- a/llvm/lib/CodeGen/MachineCSE.cpp
+++ b/llvm/lib/CodeGen/MachineCSE.cpp
@@ -184,7 +184,7 @@ bool MachineCSE::PerformTrivialCopyPropagation(MachineInstr *MI,
       continue;
     bool OnlyOneUse = MRI->hasOneNonDBGUse(Reg);
     MachineInstr *DefMI = MRI->getVRegDef(Reg);
-    if (!DefMI->isCopy())
+    if (!DefMI || !DefMI->isCopy())
       continue;
     Register SrcReg = DefMI->getOperand(1).getReg();
     if (!SrcReg.isVirtual())
diff --git a/llvm/test/CodeGen/AMDGPU/machine-cse-copyprop.mir b/llvm/test/CodeGen/AMDGPU/machine-cse-copyprop.mir
new file mode 100644
index 0000000000000..ab759657d5d7a
--- /dev/null
+++ b/llvm/test/CodeGen/AMDGPU/machine-cse-copyprop.mir
@@ -0,0 +1,21 @@
+# RUN: llc -mtriple=amdgcn -run-pass=machine-cse -verify-machineinstrs -o - %s | FileCheck %s
+
+# Test to ensure that this does not crash on undefs
+# CHECK-LABEL: name: machine-cse-copyprop
+# CHECK: IMPLICIT_DEF
+# CHECK-NOT: COPY
+# CHECK: S_ADD_I32
+---
+name: machine-cse-copyprop
+tracksRegLiveness: true
+body:               |
+  bb.0:
+    %0:sreg_32 = IMPLICIT_DEF
+    %1:sreg_32 = IMPLICIT_DEF
+    %2:sreg_32 = COPY %0
+    %3:sreg_32 = COPY %1
+    %4:sreg_64 = REG_SEQUENCE undef %10:sreg_32, %subreg.sub0, %2:sreg_32, %subreg.sub1
+    %5:sreg_64 = REG_SEQUENCE undef %11:sreg_32, %subreg.sub0, %3:sreg_32, %subreg.sub1
+    %6:sreg_32 = S_ADD_I32 %4.sub1:sreg_64, %5.sub1:sreg_64, implicit-def $scc
+
+...

``````````

</details>


https://github.com/llvm/llvm-project/pull/97413