[llvm] [CodeGen] Use first EHLabel as a stop gate for live range shrinking (PR #114195)

[via llvm-commits]

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@@ -135,6 +137,13 @@ bool LiveRangeShrink::runOnMachineFunction(MachineFunction &MF) {
         continue;
       if (MI.mayStore())
         SawStore = true;
+      if (IsEHPad && !SawEHLabel && MI.isEHLabel() && Next != MBB.end()) {
+        // If MI is the first EHLabel of an EHPad, it should become a
+        // barrier for code motion. IOM is rebuild from the next instruction
+        // to prevent later instructions from being moved before this MI.
+        SawEHLabel = true;
+        BuildInstOrderMap(Next, IOM);
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MuellerMP wrote:

Ah yes - I think I get what you were hinting at now =)
So i cant SkipPHIsLabelsAndDebug in every case since we will miss the optimization in the [original test](https://github.com/llvm/llvm-project/blob/main/llvm/test/CodeGen/X86/lrshrink.ll) which relies on moving uses of phis to their defs.
But we should be able to utilize the skip in the EHPad case since the assumption of ehlabels being the first non phi should still hold.

https://github.com/llvm/llvm-project/pull/114195