[DebugInfo][JumpThreading] Fix missing debug location updates for br instructions (#96889)

Fix #96885 .

Author: Apochens

llvm/lib/Transforms/Scalar/JumpThreading.cpp

@@ -1038,7 +1038,8 @@ bool JumpThreadingPass::processBlock(BasicBlock *BB) {
 
     LLVM_DEBUG(dbgs() << "  In block '" << BB->getName()
                       << "' folding undef terminator: " << *BBTerm << '\n');
-    BranchInst::Create(BBTerm->getSuccessor(BestSucc), BBTerm->getIterator());
+    Instruction *NewBI = BranchInst::Create(BBTerm->getSuccessor(BestSucc), BBTerm->getIterator());
+    NewBI->setDebugLoc(BBTerm->getDebugLoc());
     ++NumFolds;
     BBTerm->eraseFromParent();
     DTU->applyUpdatesPermissive(Updates);
@@ -1657,7 +1658,8 @@ bool JumpThreadingPass::processThreadableEdges(Value *Cond, BasicBlock *BB,
 
       // Finally update the terminator.
       Instruction *Term = BB->getTerminator();
-      BranchInst::Create(OnlyDest, Term->getIterator());
+      Instruction *NewBI = BranchInst::Create(OnlyDest, Term->getIterator());
+      NewBI->setDebugLoc(Term->getDebugLoc());
       ++NumFolds;
       Term->eraseFromParent();
       DTU->applyUpdatesPermissive(Updates);

llvm/test/Transforms/JumpThreading/preserving-debugloc-br.ll

@@ -0,0 +1,114 @@
+; RUN: opt -S -passes=jump-threading < %s | FileCheck %s
+
+; @process_block_branch checks that JumpThreading's processBlock() propagates 
+; the debug location to the new branch instruction.
+
+; @process_threadable_edges_branch checks that JumpThreading's processThreadableEdges()
+; propagates the debug location to the new branch instruction.
+
+define i32 @process_block_branch(i32 %action) #0 !dbg !5 {
+; CHECK-LABEL: define i32 @process_block_branch(
+; CHECK:       for.cond:
+; CHECK-NEXT:    br label %for.cond, !dbg [[DBG10:![0-9]+]]
+;
+entry:
+  switch i32 %action, label %lor.rhs [
+  i32 1, label %if.then
+  i32 0, label %lor.end
+  ], !dbg !8
+
+if.then:                                          ; preds = %for.cond, %lor.end, %entry
+  ret i32 undef, !dbg !9
+
+lor.rhs:                                          ; preds = %entry
+  br label %lor.end, !dbg !10
+
+lor.end:                                          ; preds = %lor.rhs, %entry
+  %cmp103 = xor i1 undef, undef, !dbg !11
+  br i1 %cmp103, label %for.cond, label %if.then, !dbg !12
+
+for.cond:                                         ; preds = %for.body, %lor.end
+  br i1 undef, label %if.then, label %for.body, !dbg !13
+
+for.body:                                         ; preds = %for.cond
+  br label %for.cond, !dbg !14
+}
+
+define void @process_threadable_edges_branch(i32 %value) #0 !dbg !15 {
+; CHECK-LABEL: define void @process_threadable_edges_branch(
+; CHECK:    L0:
+; CHECK:      br label %L2, !dbg [[DBG17:![0-9]+]]
+;
+entry:
+  %cmp = icmp eq i32 %value, 32, !dbg !16
+  %add = add i32 %value, 64, !dbg !17
+  br i1 %cmp, label %L0, label %L2, !dbg !18
+
+L0:                                               ; preds = %entry
+  %0 = call i32 @f2(), !dbg !19
+  %1 = call i32 @f2(), !dbg !20
+  switch i32 %add, label %L3 [
+  i32 32, label %L1
+  i32 96, label %L2
+  ], !dbg !21
+
+L1:                                               ; preds = %L0
+  call void @f3(), !dbg !22
+  ret void, !dbg !23
+
+L2:                                               ; preds = %L0, %entry
+  call void @f4(i32 %add), !dbg !24
+  ret void, !dbg !25
+
+L3:                                               ; preds = %L0
+  call void @f3(), !dbg !26
+  ret void, !dbg !27
+}
+
+declare i32 @f1()
+
+declare i32 @f2()
+
+declare void @f3()
+
+declare void @f4(i32)
+
+attributes #0 = { nounwind }
+
+!llvm.dbg.cu = !{!0}
+!llvm.debugify = !{!2, !3}
+!llvm.module.flags = !{!4}
+
+;.
+; CHECK: [[DBG10]] = !DILocation(line: 6,
+; CHECK: [[DBG17]] = !DILocation(line: 13,
+;.
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C, file: !1, producer: "debugify", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug)
+!1 = !DIFile(filename: "temp.ll", directory: "/")
+!2 = !{i32 30}
+!3 = !{i32 0}
+!4 = !{i32 2, !"Debug Info Version", i32 3}
+!5 = distinct !DISubprogram(name: "process_block_branch", linkageName: "process_block_branch", 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 = distinct !DISubprogram(name: "process_threadable_edges_branch", linkageName: "process_threadable_edges_branch", scope: null, file: !1, line: 8, type: !6, scopeLine: 8, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0)
+!16 = !DILocation(line: 8, column: 1, scope: !15)
+!17 = !DILocation(line: 9, column: 1, scope: !15)
+!18 = !DILocation(line: 10, column: 1, scope: !15)
+!19 = !DILocation(line: 11, column: 1, scope: !15)
+!20 = !DILocation(line: 12, column: 1, scope: !15)
+!21 = !DILocation(line: 13, column: 1, scope: !15)
+!22 = !DILocation(line: 14, column: 1, scope: !15)
+!23 = !DILocation(line: 15, column: 1, scope: !15)
+!24 = !DILocation(line: 16, column: 1, scope: !15)
+!25 = !DILocation(line: 17, column: 1, scope: !15)
+!26 = !DILocation(line: 18, column: 1, scope: !15)
+!27 = !DILocation(line: 19, column: 1, scope: !15)