LoopSink: Don't sink into EH pads (PR38462)

[hans]

Summary

In the PR, LoopSink was trying to sink into a catchswitch block, which doesn't have a valid insertion point.

This isn't very elegant, but should stop the bug at least.

[rnk]

lib/Transforms/Scalar/LoopSink.cpp

157

This will return true for landingpads and cleanuppads, which we can probably sink into just fine. We can limit this to catchswitches, as they are the only blocks that have no insertion point. I guess the most generic way to test would be:

if (BB->getFirstInsertionPt() == BB->end())

[hans]

Do the general thing: check for the block not having an insertion point.

[rnk]

lgtm, thanks for following up on the bug!

lib/Transforms/Scalar/LoopSink.cpp

if (adjustedSumFreq(BBsDominatedByColdestBB, BFI) >
         BFI.getBlockFreq(ColdestBB)) {
       for (BasicBlock *DominatedBB : BBsDominatedByColdestBB) {
         BBsToSinkInto.erase(DominatedBB);
       }
       BBsToSinkInto.insert(ColdestBB);
     }
   }
 
+  // Can't sink into exception handling blocks.
+  for (BasicBlock *BB : BBsToSinkInto) {
+    if (BB->isEHPad()) {
+      BBsToSinkInto.clear();
+      break;
+    }
+  }
+
   // If the total frequency of BBsToSinkInto is larger than preheader frequency,
   // do not sink.
   if (adjustedSumFreq(BBsToSinkInto, BFI) >
       BFI.getBlockFreq(L.getLoopPreheader()))
     BBsToSinkInto.clear();
   return BBsToSinkInto;
 }
 

test/Transforms/LICM/loopsink-pr38462.ll

+; RUN: opt -S -loop-sink < %s | FileCheck %s
+
+target datalayout = "e-m:w-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-pc-windows-msvc19.13.26128"
+
+%struct.FontInfoData = type { i32 (...)** }
+%struct.S = type { i8 }
+
+; CHECK: @pr38462
+; Make sure not to assert by trying to sink into catch.dispatch.
+
+define void @pr38462(%struct.FontInfoData* %this) personality i8* bitcast (i32 (...)* @__C_specific_handler to i8*) !prof !1 {
+entry:
+  %s = alloca %struct.S
+  %call6 = call i32 @f()
+  %tobool7 = icmp eq i32 %call6, 0
+  br i1 %tobool7, label %for.body.lr.ph, label %for.cond.cleanup
+
+for.body.lr.ph:
+  %0 = getelementptr inbounds %struct.S, %struct.S* %s, i64 0, i32 0
+  br label %for.body
+
+for.cond.cleanup.loopexit:
+  br label %for.cond.cleanup
+
+for.cond.cleanup:
+  ret void
+
+for.body:
+  %call2 = invoke i32 @f() to label %__try.cont unwind label %catch.dispatch
+
+catch.dispatch:
+  %1 = catchswitch within none [label %__except] unwind to caller
+
+__except:
+  %2 = catchpad within %1 [i8* null]
+  catchret from %2 to label %__except3
+
+__except3:
+  call void @llvm.lifetime.start.p0i8(i64 1, i8* nonnull %0)
+  %call.i = call zeroext i1 @g(%struct.S* nonnull %s)
+  br i1 %call.i, label %if.then.i, label %exit
+
+if.then.i:
+  %call2.i = call i32 @f()
+  br label %exit
+
+exit:
+  call void @llvm.lifetime.end.p0i8(i64 1, i8* nonnull %0)
+  br label %__try.cont
+
+__try.cont:
+  %call = call i32 @f()
+  %tobool = icmp eq i32 %call, 0
+  br i1 %tobool, label %for.body, label %for.cond.cleanup.loopexit
+}
+
+declare i32 @__C_specific_handler(...)
+declare i32 @f()
+declare zeroext i1 @g(%struct.S*)
+declare void @llvm.lifetime.start.p0i8(i64, i8* nocapture)
+declare void @llvm.lifetime.end.p0i8(i64, i8* nocapture)
+
+!1 = !{!"function_entry_count", i64 1}
+