fix crash

Author: OCHyams

llvm/lib/CodeGen/BranchFolding.cpp

@@ -2098,6 +2098,11 @@ bool BranchFolder::HoistCommonCodeInSuccs(MachineBasicBlock *MBB) {
         MBB->insert(Loc, &*DI);
         return;
       }
+      // Deleting a DBG_PHI results in an undef at the referenced DBG_INSTR_REF.
+      if (DI->isDebugPHI()) {
+        DI->eraseFromParent();
+        return;
+      }
 
       DI->setDebugValueUndef();
       DI->moveBefore(&*Loc);

llvm/test/DebugInfo/X86/branch-folder-dbg.mir

@@ -6,6 +6,8 @@
 ##
 ## The MIR debug instructions have been modified by hand in order to check they
 ## can be killed.
+##
+## Check DBG_PHIs are deleted rather than hoisted.
 
 # CHECK: bb.0
 # CHECK:      CALL64pcrel32 @f, csr_64, implicit $rsp, implicit $ssp, implicit-def $rsp, implicit-def $ssp, implicit-def $rax
@@ -93,6 +95,8 @@ body:             |
 
   bb.1.if.then:
     successors: %bb.3(0x80000000)
+
+    DBG_PHI $esp, 3
     DBG_VALUE $esi, $noreg, !11, !DIExpression(),  debug-location !13
     $edi = MOV32r0 implicit-def dead $eflags, debug-instr-number 1, debug-location !14
     DBG_INSTR_REF !11, !DIExpression(DW_OP_LLVM_arg, 0), dbg-instr-ref(1, 0),  debug-location !13
@@ -103,6 +107,7 @@ body:             |
   bb.2.if.else:
     successors: %bb.3(0x80000000)
 
+    DBG_PHI $esp, 4
     DBG_VALUE $esp, $noreg, !11, !DIExpression(), debug-location !13
     $edi = MOV32r0 implicit-def dead $eflags, debug-instr-number 2, debug-location !16
     DBG_INSTR_REF !11, !DIExpression(DW_OP_LLVM_arg, 0), dbg-instr-ref(2, 0),  debug-location !13