[InstCombine] Adjusting bswap pattern matching to hold for And/Shift …

…mixed case

Differential Revision: https://reviews.llvm.org/D45731

Change-Id: I85d4226504e954933c41598327c91b2d08192a9d
llvm-svn: 331257

llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp

@@ -1675,7 +1675,18 @@ Instruction *InstCombiner::MatchBSwap(BinaryOperator &I) {
   bool OrOfAnds = match(Op0, m_And(m_Value(), m_Value())) &&
                   match(Op1, m_And(m_Value(), m_Value()));
 
-  if (!OrOfOrs && !OrOfShifts && !OrOfAnds)
+  // (A << B) | (C & D)                              -> bswap if possible.
+  // The bigger pattern here is ((A & C1) << C2) | ((B >> C2) & C1), which is a
+  // part of the bswap idiom for specific values of C1, C2 (e.g. C1 = 16711935,
+  // C2 = 8 for i32).
+  // This pattern can occur when the operands of the 'or' are not canonicalized
+  // for some reason (not having only one use, for example).
+  bool OrOfAndAndSh = (match(Op0, m_LogicalShift(m_Value(), m_Value())) &&
+                       match(Op1, m_And(m_Value(), m_Value()))) ||
+                      (match(Op0, m_And(m_Value(), m_Value())) &&
+                       match(Op1, m_LogicalShift(m_Value(), m_Value())));
+
+  if (!OrOfOrs && !OrOfShifts && !OrOfAnds && !OrOfAndAndSh)
     return nullptr;
 
   SmallVector<Instruction*, 4> Insts;

llvm/test/Transforms/InstCombine/bswap.ll

@@ -116,7 +116,7 @@ define i32 @bswap32_and_first(i32 %x) {
   ret i32 %bswap
 }
 
-; FIXME: Extra use should not prevent matching to bswap.
+; Extra use should not prevent matching to bswap.
 ; swaphalf = (x << 16 | x >> 16)
 ; ((swaphalf & 0x00ff00ff) << 8) | ((swaphalf >> 8) & 0x00ff00ff)
 
@@ -126,10 +126,7 @@ define i32 @bswap32_and_first_extra_use(i32 %x) {
 ; CHECK-NEXT:    [[SHR:%.*]] = lshr i32 %x, 16
 ; CHECK-NEXT:    [[SWAPHALF:%.*]] = or i32 [[SHL]], [[SHR]]
 ; CHECK-NEXT:    [[T:%.*]] = and i32 [[SWAPHALF]], 16711935
-; CHECK-NEXT:    [[TSHL:%.*]] = shl nuw i32 [[T]], 8
-; CHECK-NEXT:    [[B:%.*]] = lshr i32 [[SWAPHALF]], 8
-; CHECK-NEXT:    [[BAND:%.*]] = and i32 [[B]], 16711935
-; CHECK-NEXT:    [[BSWAP:%.*]] = or i32 [[TSHL]], [[BAND]]
+; CHECK-NEXT:    [[BSWAP:%.*]] = call i32 @llvm.bswap.i32(i32 %x)
 ; CHECK-NEXT:    call void @extra_use(i32 [[T]])
 ; CHECK-NEXT:    ret i32 [[BSWAP]]
 ;