[InstCombine] avoid breaking up bitcasted vector min/max patterns (PR32306)

As the related tests show, we're not canonicalizing to this form for scalars or vectors yet,
but this solves the immediate problem in:
https://bugs.llvm.org/show_bug.cgi?id=32306

llvm-svn: 297989

1 files changed, 10 insertions, 0 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp b/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
index b8c1daab3f6..84dace5db76 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
@@ -120,6 +120,16 @@ static Constant *getSelectFoldableConstant(Instruction *I) {
 /// We have (select c, TI, FI), and we know that TI and FI have the same opcode.
 Instruction *InstCombiner::foldSelectOpOp(SelectInst &SI, Instruction *TI,
                                           Instruction *FI) {
+  // Don't break up min/max patterns. The hasOneUse checks below prevent that
+  // for most cases, but vector min/max with bitcasts can be transformed. If the
+  // one-use restrictions are eased for other patterns, we still don't want to
+  // obfuscate min/max.
+  if ((match(&SI, m_SMin(m_Value(), m_Value())) ||
+       match(&SI, m_SMax(m_Value(), m_Value())) ||
+       match(&SI, m_UMin(m_Value(), m_Value())) ||
+       match(&SI, m_UMax(m_Value(), m_Value()))))
+    return nullptr;
+
   // If this is a cast from the same type, merge.
   if (TI->getNumOperands() == 1 && TI->isCast()) {
     Type *FIOpndTy = FI->getOperand(0)->getType();