[PATCH] D124426: [InstCombine] Remove the undef-related workaround code in visitSelectInst

[Juneyoung Lee via Phabricator via llvm-commits]

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This patch removes an old hack in visitSelectInst that was written to avoid miscompilation bugs in loop unswitch.
(Added via https://reviews.llvm.org/D35811)

The legacy loop unswitch pass will be removed after D124376 <https://reviews.llvm.org/D124376>, and the new simple loop unswitch pass correctly uses freeze to avoid introducing UB after D124252 <https://reviews.llvm.org/D124252>.

Since the hack is not necessary anymore, this patch removes it.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D124426

Files:
  llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp


Index: llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
===================================================================
--- llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
+++ llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
@@ -2567,22 +2567,6 @@
   Value *FalseVal = SI.getFalseValue();
   Type *SelType = SI.getType();
 
-  // FIXME: Remove this workaround when freeze related patches are done.
-  // For select with undef operand which feeds into an equality comparison,
-  // don't simplify it so loop unswitch can know the equality comparison
-  // may have an undef operand. This is a workaround for PR31652 caused by
-  // descrepancy about branch on undef between LoopUnswitch and GVN.
-  if (match(TrueVal, m_Undef()) || match(FalseVal, m_Undef())) {
-    if (llvm::any_of(SI.users(), [&](User *U) {
-          ICmpInst *CI = dyn_cast<ICmpInst>(U);
-          if (CI && CI->isEquality())
-            return true;
-          return false;
-        })) {
-      return nullptr;
-    }
-  }
-
   if (Value *V = SimplifySelectInst(CondVal, TrueVal, FalseVal,
                                     SQ.getWithInstruction(&SI)))
     return replaceInstUsesWith(SI, V);


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