[DebugInfo][TailCallElim] Drop the debug location of AccRecInstrNew

[Apochens]

Fix #95731 .

[llvmbot]

@llvm/pr-subscribers-debuginfo

@llvm/pr-subscribers-llvm-transforms

Author: Shan Huang (Apochens)

Changes

Fix #95731 .

---

Full diff: https://github.com/llvm/llvm-project/pull/95742.diff

2 Files Affected:

• (modified) llvm/lib/Transforms/Scalar/TailRecursionElimination.cpp (+2)
• (added) llvm/test/Transforms/TailCallElim/dropping_debugloc_acc_rec_inst_rnew.ll (+109)

diff --git a/llvm/lib/Transforms/Scalar/TailRecursionElimination.cpp b/llvm/lib/Transforms/Scalar/TailRecursionElimination.cpp
index bc4b6de2f07f1..f413e4e1c15ac 100644
--- a/llvm/lib/Transforms/Scalar/TailRecursionElimination.cpp
+++ b/llvm/lib/Transforms/Scalar/TailRecursionElimination.cpp
@@ -779,6 +779,7 @@ void TailRecursionEliminator::cleanupAndFinalize() {
           AccRecInstrNew->setOperand(AccRecInstr->getOperand(0) == AccPN,
                                      RI->getOperand(0));
           AccRecInstrNew->insertBefore(RI);
+          AccRecInstrNew->dropLocation();
           RI->setOperand(0, AccRecInstrNew);
         }
       }
@@ -807,6 +808,7 @@ void TailRecursionEliminator::cleanupAndFinalize() {
           AccRecInstrNew->setOperand(AccRecInstr->getOperand(0) == AccPN,
                                      SI->getFalseValue());
           AccRecInstrNew->insertBefore(SI);
+          AccRecInstrNew->dropLocation();
           SI->setFalseValue(AccRecInstrNew);
         }
       }
diff --git a/llvm/test/Transforms/TailCallElim/dropping_debugloc_acc_rec_inst_rnew.ll b/llvm/test/Transforms/TailCallElim/dropping_debugloc_acc_rec_inst_rnew.ll
new file mode 100644
index 0000000000000..4028a472daba9
--- /dev/null
+++ b/llvm/test/Transforms/TailCallElim/dropping_debugloc_acc_rec_inst_rnew.ll
@@ -0,0 +1,109 @@
+; RUN: opt -S -passes=tailcallelim < %s | FileCheck %s
+
+; Check that TailCallElim's cleanupAndFinalize drops the debug location of `AccRecInstrNew`,
+; because it is cloned from `AccRecInstr` (`%accumulate*` in the following IR) with the 
+; debug location and inserted into the block of a different branch. 
+; @test6_multiple_returns tests that when RetSelects.empty() is false (no select instruction is inserted)
+; @test7_multiple_accumulators tests it when RetSelects.empty() is true
+
+define i32 @test6_multiple_returns(i32 %x, i32 %y) local_unnamed_addr !dbg !5 {
+; CHECK-LABEL: define i32 @test6_multiple_returns(
+; CHECK:  case0:
+; CHECK:    [[ACCUMULATOR_RET_TR2:%.*]] = add i32 %accumulator.tr, %helper{{$}}
+; CHECK:  case99:
+; CHECK:     [[ACCUMULATOR_RET_TR:%.*]] = add i32 %accumulator.tr, 18{{$}}
+; CHECK:  default:
+;
+entry:
+  switch i32 %x, label %default [
+    i32 0, label %case0
+    i32 99, label %case99
+  ], !dbg !8
+
+case0:                                            ; preds = %entry
+  %helper = call i32 @test6_helper(), !dbg !9
+  ret i32 %helper, !dbg !10
+
+case99:                                           ; preds = %entry
+  %sub1 = add i32 %x, -1, !dbg !11
+  %recurse1 = call i32 @test6_multiple_returns(i32 %sub1, i32 %y), !dbg !12
+  ret i32 18, !dbg !13
+
+default:                                          ; preds = %entry
+  %sub2 = add i32 %x, -1, !dbg !14
+  %recurse2 = call i32 @test6_multiple_returns(i32 %sub2, i32 %y), !dbg !15
+  %accumulate = add i32 %recurse2, %y, !dbg !16
+  ret i32 %accumulate, !dbg !17
+}
+
+declare i32 @test6_helper()
+
+define i32 @test7_multiple_accumulators(i32 %a) local_unnamed_addr !dbg !18 {
+; CHECK-LABEL: define i32 @test7_multiple_accumulators(
+; CHECK:  if.end3:
+; CHECK:    [[ACCUMULATOR_RET_TR:%.*]] = add nsw i32 %accumulator.tr, [[ACCUMULATE2:.*]]{{$}}
+; CHECK:  return:
+; CHECK:    [[ACCUMULATOR_RET_TR1:%.*]] = add nsw i32 %accumulator.tr, 0{{$}}
+;
+entry:
+  %tobool = icmp eq i32 %a, 0, !dbg !19
+  br i1 %tobool, label %return, label %if.end, !dbg !20
+
+if.end:                                           ; preds = %entry
+  %and = and i32 %a, 1, !dbg !21
+  %tobool1 = icmp eq i32 %and, 0, !dbg !22
+  %sub = add nsw i32 %a, -1, !dbg !23
+  br i1 %tobool1, label %if.end3, label %if.then2, !dbg !24
+
+if.then2:                                         ; preds = %if.end
+  %recurse1 = tail call i32 @test7_multiple_accumulators(i32 %sub), !dbg !25
+  %accumulate1 = add nsw i32 %recurse1, 1, !dbg !26
+  br label %return, !dbg !27
+
+if.end3:                                          ; preds = %if.end
+  %recurse2 = tail call i32 @test7_multiple_accumulators(i32 %sub), !dbg !28
+  %accumulate2 = mul nsw i32 %recurse2, 2, !dbg !29
+  br label %return, !dbg !30
+
+return:                                           ; preds = %if.end3, %if.then2, %entry
+  %retval.0 = phi i32 [ %accumulate1, %if.then2 ], [ %accumulate2, %if.end3 ], [ 0, %entry ], !dbg !31
+  ret i32 %retval.0, !dbg !32
+}
+
+!llvm.dbg.cu = !{!0}
+!llvm.debugify = !{!2, !3}
+!llvm.module.flags = !{!4}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C, file: !1, producer: "debugify", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug)
+!1 = !DIFile(filename: "all.ll", directory: "/")
+!2 = !{i32 24}
+!3 = !{i32 0}
+!4 = !{i32 2, !"Debug Info Version", i32 3}
+!5 = distinct !DISubprogram(name: "test6_multiple_returns", linkageName: "test6_multiple_returns", scope: null, file: !1, line: 1, type: !6, scopeLine: 1, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0)
+!6 = !DISubroutineType(types: !7)
+!7 = !{}
+!8 = !DILocation(line: 1, column: 1, scope: !5)
+!9 = !DILocation(line: 2, column: 1, scope: !5)
+!10 = !DILocation(line: 3, column: 1, scope: !5)
+!11 = !DILocation(line: 4, column: 1, scope: !5)
+!12 = !DILocation(line: 5, column: 1, scope: !5)
+!13 = !DILocation(line: 6, column: 1, scope: !5)
+!14 = !DILocation(line: 7, column: 1, scope: !5)
+!15 = !DILocation(line: 8, column: 1, scope: !5)
+!16 = !DILocation(line: 9, column: 1, scope: !5)
+!17 = !DILocation(line: 10, column: 1, scope: !5)
+!18 = distinct !DISubprogram(name: "test7_multiple_accumulators", linkageName: "test7_multiple_accumulators", scope: null, file: !1, line: 11, type: !6, scopeLine: 11, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0)
+!19 = !DILocation(line: 11, column: 1, scope: !18)
+!20 = !DILocation(line: 12, column: 1, scope: !18)
+!21 = !DILocation(line: 13, column: 1, scope: !18)
+!22 = !DILocation(line: 14, column: 1, scope: !18)
+!23 = !DILocation(line: 15, column: 1, scope: !18)
+!24 = !DILocation(line: 16, column: 1, scope: !18)
+!25 = !DILocation(line: 17, column: 1, scope: !18)
+!26 = !DILocation(line: 18, column: 1, scope: !18)
+!27 = !DILocation(line: 19, column: 1, scope: !18)
+!28 = !DILocation(line: 20, column: 1, scope: !18)
+!29 = !DILocation(line: 21, column: 1, scope: !18)
+!30 = !DILocation(line: 22, column: 1, scope: !18)
+!31 = !DILocation(line: 23, column: 1, scope: !18)
+!32 = !DILocation(line: 24, column: 1, scope: !18)

[OCHyams]

LGTM - looks like this patch prevents misleading bonus coverage

Thanks!