[BasicBlockUtils] Remove redundant llvm.dbg instructions after blocks

have been merged.

When compiling with the "-g" and enabling loop-unroll optimization, the
redundant "llvm.dbg" instructions sometimes will be generated. It has
a significant impact on compilation time in some cases.

Fixes #89073.

Author: coderchenlin

llvm/lib/Transforms/Utils/BasicBlockUtils.cpp

@@ -333,6 +333,10 @@ bool llvm::MergeBlockIntoPredecessor(BasicBlock *BB, DomTreeUpdater *DTU,
   // Finally, erase the old block and update dominator info.
   DeleteDeadBlock(BB, DTU);
 
+  // Remove redundant "llvm.dbg" instrunctions after blocks have been merged.
+  if (PredBB->getParent()->getSubprogram())
+    RemoveRedundantDbgInstrs(PredBB);
+
   return true;
 }
 

llvm/test/Transforms/SimplifyCFG/hoist-dbgvalue-inlined.ll

@@ -9,7 +9,6 @@ init:
 
 ; CHECK:  %vala = load i64, ptr %ptr
 ; CHECK-NEXT:  call void @llvm.dbg.value(metadata i64 %vala, metadata [[MD:![0-9]*]]
-; CHECK-NEXT:  call void @llvm.dbg.value(metadata i64 %vala, metadata [[MD]]
 ; CHECK-NEXT:  %valbmasked = and i64 %vala, 1
 
 a:                                              ; preds = %init

llvm/test/Transforms/SimplifyCFG/hoist-dbgvalue.ll

@@ -47,7 +47,6 @@ define i1 @hoist_with_debug2(i32 %x) !dbg !22 {
 ; CHECK-NEXT:  entry:
 ; CHECK-NEXT:    [[TOBOOL_NOT:%.*]] = icmp ugt i32 [[X:%.*]], 2
 ; CHECK-NEXT:    call void @llvm.dbg.value(metadata i32 [[X]], metadata [[META21:![0-9]+]], metadata !DIExpression()), !dbg [[DBG23:![0-9]+]]
-; CHECK-NEXT:    call void @llvm.dbg.value(metadata i32 [[X]], metadata [[META21]], metadata !DIExpression()), !dbg [[DBG23]]
 ; CHECK-NEXT:    [[DOT:%.*]] = select i1 [[TOBOOL_NOT]], i1 false, i1 true
 ; CHECK-NEXT:    ret i1 [[DOT]]
 ;