[llvm] [BOLT] Avoid EH trampolines for PIEs/DSOs (PR #117106)

[Davide Italiano via llvm-commits]

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@@ -901,8 +901,42 @@ void SplitFunctions::splitFunction(BinaryFunction &BF, SplitStrategy &S) {
   // have to be placed in the same fragment. When we split them, create
   // trampoline landing pads that will redirect the execution to real LPs.
   TrampolineSetType Trampolines;
-  if (!BC.HasFixedLoadAddress && BF.hasEHRanges() && BF.isSplit())
-    Trampolines = createEHTrampolines(BF);
+  if (!BC.HasFixedLoadAddress && BF.hasEHRanges() && BF.isSplit()) {
+    // If all landing pads for this fragment are grouped in one (potentially
+    // different) fragment, we can set LPStart to the start of that fragment
+    // and avoid trampoline code.
+    bool NeedsTrampolines = false;
+    for (FunctionFragment &FF : BF.getLayout().fragments()) {
+      // Vector of fragments that contain landing pads for this fragment.
+      SmallVector<FragmentNum, 4> LandingPadFragments;
+      for (const BinaryBasicBlock *BB : FF)
+        for (const BinaryBasicBlock *LPB : BB->landing_pads())
+          LandingPadFragments.push_back(LPB->getFragmentNum());
+
+      llvm::sort(LandingPadFragments);
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dcci wrote:

Would be useful to add a comment on why this sorting is needed

https://github.com/llvm/llvm-project/pull/117106