[SelectOpt] Don't treat LogicalAnd/LogicalOr as selects

A `select i1 %c, i1 true, i1 %d` is just an or and a `select i1 %c, i1 %d, i1 false`
is just an and. There are better treated as such in the logic of SelectOpt, allowing
the backend to optimize them to and/or directly.

Differential Revision: https://reviews.llvm.org/D138490

1 files changed, 15 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/SelectOptimize.cpp b/llvm/lib/CodeGen/SelectOptimize.cpp
index b5a8a80..a8144e4 100644
--- a/llvm/lib/CodeGen/SelectOptimize.cpp
+++ b/llvm/lib/CodeGen/SelectOptimize.cpp
@@ -515,12 +515,27 @@ void SelectOptimize::convertProfitableSIGroups(SelectGroups &ProfSIGroups) {
   }
 }
 
+static bool isSpecialSelect(SelectInst *SI) {
+  using namespace llvm::PatternMatch;
+
+  // If the select is a logical-and/logical-or then it is better treated as a
+  // and/or by the backend.
+  if (match(SI, m_CombineOr(m_LogicalAnd(m_Value(), m_Value()),
+                            m_LogicalOr(m_Value(), m_Value()))))
+    return true;
+
+  return false;
+}
+
 void SelectOptimize::collectSelectGroups(BasicBlock &BB,
                                          SelectGroups &SIGroups) {
   BasicBlock::iterator BBIt = BB.begin();
   while (BBIt != BB.end()) {
     Instruction *I = &*BBIt++;
     if (SelectInst *SI = dyn_cast<SelectInst>(I)) {
+      if (isSpecialSelect(SI))
+        continue;
+
       SelectGroup SIGroup;
       SIGroup.push_back(SI);
       while (BBIt != BB.end()) {