Recognize 16-bit bswaps by relaxing overconstrained pattern.

This implements Transforms/InstCombine/bswap.ll:test[34].

llvm-svn: 29087

1 files changed, 5 insertions, 2 deletions

diff --git a/llvm/lib/Transforms/Scalar/InstructionCombining.cpp b/llvm/lib/Transforms/Scalar/InstructionCombining.cpp
index ebefdb31a44..5273e958da2 100644
--- a/llvm/lib/Transforms/Scalar/InstructionCombining.cpp
+++ b/llvm/lib/Transforms/Scalar/InstructionCombining.cpp
@@ -2976,9 +2976,12 @@ Instruction *InstCombiner::visitOr(BinaryOperator &I) {
     if (A == Op0 || B == Op0)    // A | (A & ?)  --> A
       return ReplaceInstUsesWith(I, Op0);
 
-  // (A | B) | C  and  A | (B | C)  -> bswap if possible.
+  // (A | B) | C  and  A | (B | C)                  -> bswap if possible.
+  // (A >> B) | (C << D)  and  (A << B) | (B >> C)  -> bswap if possible.
   if (match(Op0, m_Or(m_Value(), m_Value())) ||
-      match(Op1, m_Or(m_Value(), m_Value()))) {
+      match(Op1, m_Or(m_Value(), m_Value())) ||
+      (match(Op0, m_Shift(m_Value(), m_Value())) &&
+       match(Op1, m_Shift(m_Value(), m_Value())))) {
     if (Instruction *BSwap = MatchBSwap(I))
       return BSwap;
   }