[DebugInfo] Prefer to use setKillLocation rather than replacing operands with undef

[Orlando]

Summary

NFC-ish. There is a functional change but the outputs are semantically identical. Where we might've before replaced one operand with undef (which means "this is a kill location marker") the use of setKillLocation will replace all location operands with undef (which also means "this is a kill location marker").

Related to https://discourse.llvm.org/t/auto-undef-debug-uses-of-a-deleted-value

[StephenTozer]

Simple and good, LGTM.

llvm/test/DebugInfo/NVPTX/debug-info.ll

109

Meaningful, or just whitespace sneaking in?

[Orlando]

llvm/test/DebugInfo/NVPTX/debug-info.ll

109

Whoops, it snuck in and I forgot to change it back before committing. Worth fixing in post commit?

llvm/lib/Transforms/Utils/Local.cpp

while (!DeadInsts.empty()) {
 
     I->eraseFromParent();
   }
 }
 
 bool llvm::replaceDbgUsesWithUndef(Instruction *I) {
   SmallVector<DbgVariableIntrinsic *, 1> DbgUsers;
   findDbgUsers(DbgUsers, I);
-  for (auto *DII : DbgUsers) {
-    Value *Undef = UndefValue::get(I->getType());
-    DII->replaceVariableLocationOp(I, Undef);
-  }
+  for (auto *DII : DbgUsers)
+    DII->setKillLocation();
   return !DbgUsers.empty();
 }
 
 /// areAllUsesEqual - Check whether the uses of a value are all the same.
 /// This is similar to Instruction::hasOneUse() except this will also return
 /// true when there are no uses or multiple uses that all refer to the same
 /// value.
 static bool areAllUsesEqual(Instruction *I) {
if (AdditionalValues.empty() && IsValidSalvageExpr) {
                    MaxDebugArgs) {
       DII->addVariableLocationOps(AdditionalValues, SalvagedExpr);
     } else {
       // Do not salvage using DIArgList for dbg.addr/dbg.declare, as it is
       // currently only valid for stack value expressions. Do not salvage
       // using DIArgList for dbg.assign yet. FIXME: support this.
       // Also do not salvage if the resulting DIArgList would contain an
       // unreasonably large number of values.
-      Value *Undef = UndefValue::get(I.getOperand(0)->getType());
-      DII->replaceVariableLocationOp(I.getOperand(0), Undef);
+      DII->setKillLocation();
     }
     LLVM_DEBUG(dbgs() << "SALVAGE: " << *DII << '\n');
     Salvaged = true;
   }
 
   if (Salvaged)
     return;
 
-  for (auto *DII : DbgUsers) {
-    Value *Undef = UndefValue::get(I.getType());
-    DII->replaceVariableLocationOp(&I, Undef);
-  }
+  for (auto *DII : DbgUsers)
+    DII->setKillLocation();
 }
 
 Value *getSalvageOpsForGEP(GetElementPtrInst *GEP, const DataLayout &DL,
                            uint64_t CurrentLocOps,
                            SmallVectorImpl<uint64_t> &Opcodes,
                            SmallVectorImpl<Value *> &AdditionalValues) {
   unsigned BitWidth = DL.getIndexSizeInBits(GEP->getPointerAddressSpace());
   // Rewrite a GEP into a DIExpression.

llvm/test/DebugInfo/NVPTX/debug-info.ll

 ; CHECK-DAG: .file {{[0-9]+}} "{{.*}}/usr/include{{/|\\\\}}stdlib-bsearch.h"
 ; CHECK-DAG: .file {{[0-9]+}} "{{.*}}clang/include{{/|\\\\}}stddef.h"
 ; CHECK-DAG: .file {{[0-9]+}} "{{.*}}/usr/local/cuda/include{{/|\\\\}}math_functions.hpp"
 ; CHECK-DAG: .file {{[0-9]+}} "{{.*}}clang/include{{/|\\\\}}__clang_cuda_cmath.h"
 ; CHECK-DAG: .file {{[0-9]+}} "{{.*}}/usr/local/cuda/include{{/|\\\\}}device_functions.hpp"
 ; CHECK-DAG: .file [[DEBUG_INFO_CU]] "{{.*}}debug-info.cu"
 ; CHECK-DAG: .file [[BUILTUIN_VARS_H]] "{{.*}}clang/include{{/|\\\\}}__clang_cuda_builtin_vars.h"
 
-; CHECK:  .section  .debug_abbrev
+; CHECK:    .section  .debug_abbrev
 ; CHECK-NEXT: {
 ; CHECK-NEXT:.b8 1                                   // Abbreviation Code
 ; CHECK-NEXT:.b8 17                                  // DW_TAG_compile_unit
 ; CHECK-NEXT:.b8 1                                   // DW_CHILDREN_yes
 ; CHECK-NEXT:.b8 37                                  // DW_AT_producer
 ; CHECK-NEXT:.b8 8                                   // DW_FORM_string
 ; CHECK-NEXT:.b8 19                                  // DW_AT_language
 ; CHECK-NEXT:.b8 5                                   // DW_FORM_data2

 ; CHECK-NEXT:.b8 49                                  // DW_AT_abstract_origin
 ; CHECK-NEXT:.b8 19                                  // DW_FORM_ref4
 ; CHECK-NEXT:.b8 0                                   // EOM(1)
 ; CHECK-NEXT:.b8 0                                   // EOM(2)
 ; CHECK-NEXT:.b8 0                                   // EOM(3)
 ; CHECK-NEXT: }
 ; CHECK-NEXT: .section  .debug_info
 ; CHECK-NEXT: {
-; CHECK-NEXT:.b32 10029                              // Length of Unit
+; CHECK-NEXT:.b32 10034                              // Length of Unit
 ; CHECK-NEXT:.b8 2                                   // DWARF version number
 ; CHECK-NEXT:.b8 0
 ; CHECK-NEXT:.b32 .debug_abbrev                      // Offset Into Abbrev. Section
 ; CHECK-NEXT:.b8 8                                   // Address Size (in bytes)
-; CHECK-NEXT:.b8 1                                   // Abbrev [1] 0xb:0x2726 DW_TAG_compile_unit
+; CHECK-NEXT:.b8 1                                   // Abbrev [1] 0xb:0x272b DW_TAG_compile_unit
 ; CHECK-NEXT:.b8 0                                   // DW_AT_producer
 ; CHECK-NEXT:.b8 4                                   // DW_AT_language
 ; CHECK-NEXT:.b8 0
 ; CHECK-NEXT:.b8 100                                 // DW_AT_name
 ; CHECK-NEXT:.b8 101
 ; CHECK-NEXT:.b8 98
 ; CHECK-NEXT:.b8 117
 ; CHECK-NEXT:.b8 103

 ; CHECK-NEXT:.b8 114                                 // DW_AT_name
 ; CHECK-NEXT:.b8 101
 ; CHECK-NEXT:.b8 115
 ; CHECK-NEXT:.b8 0
 ; CHECK-NEXT:.b8 12                                  // DW_AT_decl_file
 ; CHECK-NEXT:.b8 3                                   // DW_AT_decl_line
 ; CHECK-NEXT:.b32 3345                               // DW_AT_type
 ; CHECK-NEXT:.b8 0                                   // End Of Children Mark
-; CHECK-NEXT:.b8 40                                  // Abbrev [40] 0x2671:0xbf DW_TAG_subprogram
+; CHECK-NEXT:.b8 40                                  // Abbrev [40] 0x2671:0xc4 DW_TAG_subprogram
 ; CHECK-NEXT:.b64 $L__func_begin0                    // DW_AT_low_pc
 ; CHECK-NEXT:.b64 $L__func_end0                      // DW_AT_high_pc
 ; CHECK-NEXT:.b8 1                                   // DW_AT_frame_base
 ; CHECK-NEXT:.b8 156
 ; CHECK-NEXT:.b8 95                                  // DW_AT_MIPS_linkage_name
 ; CHECK-NEXT:.b8 90
 ; CHECK-NEXT:.b8 53
 ; CHECK-NEXT:.b8 115

 ; CHECK-NEXT:.b8 24                                  // DW_AT_call_column
 ; CHECK-NEXT:.b8 42                                  // Abbrev [42] 0x26f9:0x18 DW_TAG_inlined_subroutine
 ; CHECK-NEXT:.b32 9785                               // DW_AT_abstract_origin
 ; CHECK-NEXT:.b64 $L__tmp2                           // DW_AT_low_pc
 ; CHECK-NEXT:.b64 $L__tmp3                           // DW_AT_high_pc
 ; CHECK-NEXT:.b8 12                                  // DW_AT_call_file
 ; CHECK-NEXT:.b8 6                                   // DW_AT_call_line
 ; CHECK-NEXT:.b8 37                                  // DW_AT_call_column
-; CHECK-NEXT:.b8 43                                  // Abbrev [43] 0x2711:0x1e DW_TAG_inlined_subroutine
+; CHECK-NEXT:.b8 43                                  // Abbrev [43] 0x2711:0x23 DW_TAG_inlined_subroutine
 ; CHECK-NEXT:.b32 9791                               // DW_AT_abstract_origin
 ; CHECK-NEXT:.b64 $L__tmp9                           // DW_AT_low_pc
 ; CHECK-NEXT:.b64 $L__tmp10                          // DW_AT_high_pc
 ; CHECK-NEXT:.b8 12                                  // DW_AT_call_file
 ; CHECK-NEXT:.b8 8                                   // DW_AT_call_line
 ; CHECK-NEXT:.b8 5                                   // DW_AT_call_column
 ; CHECK-NEXT:.b8 44                                  // Abbrev [44] 0x2729:0x5 DW_TAG_formal_parameter
 ; CHECK-NEXT:.b32 9820                               // DW_AT_abstract_origin
+; CHECK-NEXT:.b8 44                                  // Abbrev [44] 0x272e:0x5 DW_TAG_formal_parameter
+; CHECK-NEXT:.b32 9829                               // DW_AT_abstract_origin
 ; CHECK-NEXT:.b8 0                                   // End Of Children Mark
 ; CHECK-NEXT:.b8 0                                   // End Of Children Mark
 ; CHECK-NEXT:.b8 0                                   // End Of Children Mark
 ; CHECK-NEXT: }
 ; CHECK-NEXT: .section  .debug_loc  { }
 ; CHECK-NOT: debug_
 
 ; Function Attrs: nounwind readnone