<div dir="ltr"><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Thu, Apr 29, 2021 at 12:01 AM Roman Lebedev via llvm-commits <<a href="mailto:llvm-commits@lists.llvm.org">llvm-commits@lists.llvm.org</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><br>
Author: Roman Lebedev<br>
Date: 2021-04-29T01:01:01+03:00<br>
New Revision: 1886aad9d03b95c35260d6d8013d746bd39dc94a<br>
<br>
URL: <a href="https://github.com/llvm/llvm-project/commit/1886aad9d03b95c35260d6d8013d746bd39dc94a" rel="noreferrer" target="_blank">https://github.com/llvm/llvm-project/commit/1886aad9d03b95c35260d6d8013d746bd39dc94a</a><br>
DIFF: <a href="https://github.com/llvm/llvm-project/commit/1886aad9d03b95c35260d6d8013d746bd39dc94a.diff" rel="noreferrer" target="_blank">https://github.com/llvm/llvm-project/commit/1886aad9d03b95c35260d6d8013d746bd39dc94a.diff</a><br>
<br>
LOG: [SimplifyCFG] Common code sinking: relax restriction on non-uncond predecessors<br>
<br>
While we have a known profitability issue for sinking in presence of<br>
non-unconditional predecessors, there isn't any known issues<br>
for having multiple such non-unconditional predecessors,<br>
so said restriction appears to be artificial. Lift it.<br>
<br>
Added: <br>
<br>
<br>
Modified: <br>
    llvm/lib/Transforms/Utils/SimplifyCFG.cpp<br>
    llvm/test/Transforms/SimplifyCFG/X86/sink-common-code.ll<br>
<br>
Removed: <br>
<br>
<br>
<br>
################################################################################<br>
diff  --git a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp<br>
index 77c0890fa91e..0704c5f2321a 100644<br>
--- a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp<br>
+++ b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp<br>
@@ -1988,15 +1988,13 @@ static bool SinkCommonCodeFromPredecessors(BasicBlock *BB,<br>
   //         [ end ]<br>
   //<br>
   SmallVector<BasicBlock*,4> UnconditionalPreds;<br>
-  Instruction *Cond = nullptr;<br>
-  for (auto *B : predecessors(BB)) {<br>
-    auto *T = B->getTerminator();<br>
-    if (isa<BranchInst>(T) && cast<BranchInst>(T)->isUnconditional())<br>
-      UnconditionalPreds.push_back(B);<br>
-    else if ((isa<BranchInst>(T) || isa<SwitchInst>(T)) && !Cond)<br>
-      Cond = T;<br>
+  bool AllPredsAreUnconditional = false;<br>
+  for (auto *PredBB : predecessors(BB)) {<br>
+    auto *PredBr = dyn_cast<BranchInst>(PredBB->getTerminator());<br>
+    if (PredBr && PredBr->isUnconditional())<br>
+      UnconditionalPreds.push_back(PredBB);<br>
     else<br>
-      return false;<br>
+      AllPredsAreUnconditional = true;<br></blockquote><div><br></div><div>Is the name of this variable inverted? You're setting it to true when there is a conditional branch.<br></div><div><br></div><div>Nikita<br></div><div> </div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
   }<br>
   if (UnconditionalPreds.size() < 2)<br>
     return false;<br>
@@ -2063,7 +2061,7 @@ static bool SinkCommonCodeFromPredecessors(BasicBlock *BB,<br>
<br>
   bool Changed = false;<br>
<br>
-  if (Cond) {<br>
+  if (AllPredsAreUnconditional) {<br>
     // It is always legal to sink common instructions from unconditional<br>
     // predecessors. However, if not all predecessors are unconditional,<br>
     // this transformation might be pessimizing. So as a rule of thumb,<br>
<br>
diff  --git a/llvm/test/Transforms/SimplifyCFG/X86/sink-common-code.ll b/llvm/test/Transforms/SimplifyCFG/X86/sink-common-code.ll<br>
index ade36c7019d1..a85ad8e69a20 100644<br>
--- a/llvm/test/Transforms/SimplifyCFG/X86/sink-common-code.ll<br>
+++ b/llvm/test/Transforms/SimplifyCFG/X86/sink-common-code.ll<br>
@@ -1538,14 +1538,11 @@ define void @multiple_cond_preds(i1 %c0, i1 %c1, i1 %c2) {<br>
 ; CHECK-NEXT:    br i1 [[C0:%.*]], label [[DISPATCH1:%.*]], label [[DISPATCH2:%.*]]<br>
 ; CHECK:       dispatch1:<br>
 ; CHECK-NEXT:    call void @direct_callee2()<br>
-; CHECK-NEXT:    br i1 [[C1:%.*]], label [[UNCOND_PRED0:%.*]], label [[END:%.*]]<br>
+; CHECK-NEXT:    br i1 [[C1:%.*]], label [[END_SINK_SPLIT:%.*]], label [[END:%.*]]<br>
 ; CHECK:       dispatch2:<br>
 ; CHECK-NEXT:    call void @direct_callee3()<br>
-; CHECK-NEXT:    br i1 [[C2:%.*]], label [[UNCOND_PRED1:%.*]], label [[END]]<br>
-; CHECK:       uncond_pred0:<br>
-; CHECK-NEXT:    call void @direct_callee()<br>
-; CHECK-NEXT:    br label [[END]]<br>
-; CHECK:       uncond_pred1:<br>
+; CHECK-NEXT:    br i1 [[C2:%.*]], label [[END_SINK_SPLIT]], label [[END]]<br>
+; CHECK:       end.sink.split:<br>
 ; CHECK-NEXT:    call void @direct_callee()<br>
 ; CHECK-NEXT:    br label [[END]]<br>
 ; CHECK:       end:<br>
<br>
<br>
<br>
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</blockquote></div></div>