[llvm] [DebugInfo][SimpleLoopUnswitch] Fix missing debug location updates (PR #97662)

[Shan Huang via llvm-commits]

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@@ -0,0 +1,75 @@
+; RUN: opt -passes='simple-loop-unswitch<nontrivial>' -S < %s | FileCheck %s
+
+define i32 @basic(i32 %N, i1 %cond, i32 %select_input) !dbg !5 {
+; CHECK-LABEL: define i32 @basic(
+
+; Check that SimpleLoopUnswitch's unswitchNontrivialInvariants() drops the
+; debug location of the hoisted terminator and doesn't give any debug location
+; to the new freeze, since it's inserted in a hoist block.
+; Also check that in unswitchNontrivialInvariants(), the new br instruction
+; inherits the debug location of the old terminator in the same block.
+
+; CHECK:       entry:
+; CHECK-NEXT:    [[COND_FR:%.*]] = freeze i1 [[COND:%.*]]{{$}}
+; CHECK-NEXT:    br i1 [[COND_FR]], label %[[ENTRY_SPLIT_US:.*]], label %[[ENTRY_SPLIT:.*]]{{$}}
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Apochens wrote:

Oh, I think we are talking about the same unconditional branch and I did not state it clearly. The conditional branch in the second code snippet just has the same number of `!dbg` with the unconditional branch in the first code snippet, i.e., `!dbg !8`. However, `!dbg !8` in the first snippet points to line 1 while it points to line 6 in the second snippet. So, the debug location of the unconditional branch did not get propagated to the conditional branch (they just have the same metadata number).

https://github.com/llvm/llvm-project/pull/97662