[InstCombine] matchOrConcat - match BITREVERSE

Fold or(zext(bitreverse(x)),shl(zext(bitreverse(y)),bw/2) -> bitreverse(or(zext(x),shl(zext(y),bw/2))

Practically this is the same as the BSWAP pattern so we might as well handle it.

llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp

@@ -2159,20 +2159,30 @@ static Instruction *matchOrConcat(Instruction &Or,
       LowerSrc->getType()->getScalarSizeInBits() != HalfWidth)
     return nullptr;
 
-  // Find matching bswap instructions.
-  // TODO: Add more patterns (bitreverse?)
+  auto ConcatIntrinsicCalls = [&](Intrinsic::ID id, Value *Lo, Value *Hi) {
+    Value *NewLower = Builder.CreateZExt(Lo, Ty);
+    Value *NewUpper = Builder.CreateZExt(Hi, Ty);
+    NewUpper = Builder.CreateShl(NewUpper, HalfWidth);
+    Value *BinOp = Builder.CreateOr(NewLower, NewUpper);
+    Function *F = Intrinsic::getDeclaration(Or.getModule(), id, Ty);
+    return Builder.CreateCall(F, BinOp);
+  };
+
+  // BSWAP: Push the concat down, swapping the lower/upper sources.
+  // concat(bswap(x),bswap(y)) -> bswap(concat(x,y))
   Value *LowerBSwap, *UpperBSwap;
-  if (!match(LowerSrc, m_BSwap(m_Value(LowerBSwap))) ||
-      !match(UpperSrc, m_BSwap(m_Value(UpperBSwap))))
-    return nullptr;
+  if (match(LowerSrc, m_BSwap(m_Value(LowerBSwap))) &&
+      match(UpperSrc, m_BSwap(m_Value(UpperBSwap))))
+    return ConcatIntrinsicCalls(Intrinsic::bswap, UpperBSwap, LowerBSwap);
 
-  // Push the concat down, swapping the lower/upper sources.
-  Value *NewLower = Builder.CreateZExt(UpperBSwap, Ty);
-  Value *NewUpper = Builder.CreateZExt(LowerBSwap, Ty);
-  NewUpper = Builder.CreateShl(NewUpper, HalfWidth);
-  Value *BinOp = Builder.CreateOr(NewLower, NewUpper);
-  Function *F = Intrinsic::getDeclaration(Or.getModule(), Intrinsic::bswap, Ty);
-  return Builder.CreateCall(F, BinOp);
+  // BITREVERSE: Push the concat down, swapping the lower/upper sources.
+  // concat(bitreverse(x),bitreverse(y)) -> bitreverse(concat(x,y))
+  Value *LowerBRev, *UpperBRev;
+  if (match(LowerSrc, m_BitReverse(m_Value(LowerBRev))) &&
+      match(UpperSrc, m_BitReverse(m_Value(UpperBRev))))
+    return ConcatIntrinsicCalls(Intrinsic::bitreverse, UpperBRev, LowerBRev);
+
+  return nullptr;
 }
 
 /// If all elements of two constant vectors are 0/-1 and inverses, return true.

llvm/test/Transforms/InstCombine/or-concat.ll

@@ -72,16 +72,8 @@ declare i32 @llvm.bswap.i32(i32)
 
 define i64 @concat_bitreverse32_unary_split(i64 %a0) {
 ; CHECK-LABEL: @concat_bitreverse32_unary_split(
-; CHECK-NEXT:    [[TMP1:%.*]] = lshr i64 [[A0:%.*]], 32
-; CHECK-NEXT:    [[TMP2:%.*]] = trunc i64 [[TMP1]] to i32
-; CHECK-NEXT:    [[TMP3:%.*]] = trunc i64 [[A0]] to i32
-; CHECK-NEXT:    [[TMP4:%.*]] = tail call i32 @llvm.bitreverse.i32(i32 [[TMP2]])
-; CHECK-NEXT:    [[TMP5:%.*]] = tail call i32 @llvm.bitreverse.i32(i32 [[TMP3]])
-; CHECK-NEXT:    [[TMP6:%.*]] = zext i32 [[TMP4]] to i64
-; CHECK-NEXT:    [[TMP7:%.*]] = zext i32 [[TMP5]] to i64
-; CHECK-NEXT:    [[TMP8:%.*]] = shl nuw i64 [[TMP7]], 32
-; CHECK-NEXT:    [[TMP9:%.*]] = or i64 [[TMP8]], [[TMP6]]
-; CHECK-NEXT:    ret i64 [[TMP9]]
+; CHECK-NEXT:    [[TMP1:%.*]] = call i64 @llvm.bitreverse.i64(i64 [[A0:%.*]])
+; CHECK-NEXT:    ret i64 [[TMP1]]
 ;
   %1 = lshr i64 %a0, 32
   %2 = trunc i64 %1 to i32
@@ -98,15 +90,10 @@ define i64 @concat_bitreverse32_unary_split(i64 %a0) {
 define i64 @concat_bitreverse32_unary_flip(i64 %a0) {
 ; CHECK-LABEL: @concat_bitreverse32_unary_flip(
 ; CHECK-NEXT:    [[TMP1:%.*]] = lshr i64 [[A0:%.*]], 32
-; CHECK-NEXT:    [[TMP2:%.*]] = trunc i64 [[TMP1]] to i32
-; CHECK-NEXT:    [[TMP3:%.*]] = trunc i64 [[A0]] to i32
-; CHECK-NEXT:    [[TMP4:%.*]] = tail call i32 @llvm.bitreverse.i32(i32 [[TMP2]])
-; CHECK-NEXT:    [[TMP5:%.*]] = tail call i32 @llvm.bitreverse.i32(i32 [[TMP3]])
-; CHECK-NEXT:    [[TMP6:%.*]] = zext i32 [[TMP4]] to i64
-; CHECK-NEXT:    [[TMP7:%.*]] = zext i32 [[TMP5]] to i64
-; CHECK-NEXT:    [[TMP8:%.*]] = shl nuw i64 [[TMP6]], 32
-; CHECK-NEXT:    [[TMP9:%.*]] = or i64 [[TMP8]], [[TMP7]]
-; CHECK-NEXT:    ret i64 [[TMP9]]
+; CHECK-NEXT:    [[TMP2:%.*]] = shl i64 [[A0]], 32
+; CHECK-NEXT:    [[TMP3:%.*]] = or i64 [[TMP1]], [[TMP2]]
+; CHECK-NEXT:    [[TMP4:%.*]] = call i64 @llvm.bitreverse.i64(i64 [[TMP3]])
+; CHECK-NEXT:    ret i64 [[TMP4]]
 ;
   %1 = lshr i64 %a0, 32
   %2 = trunc i64 %1 to i32
@@ -122,13 +109,12 @@ define i64 @concat_bitreverse32_unary_flip(i64 %a0) {
 
 define i64 @concat_bitreverse32_binary(i32 %a0, i32 %a1) {
 ; CHECK-LABEL: @concat_bitreverse32_binary(
-; CHECK-NEXT:    [[TMP1:%.*]] = tail call i32 @llvm.bitreverse.i32(i32 [[A0:%.*]])
-; CHECK-NEXT:    [[TMP2:%.*]] = tail call i32 @llvm.bitreverse.i32(i32 [[A1:%.*]])
-; CHECK-NEXT:    [[TMP3:%.*]] = zext i32 [[TMP1]] to i64
-; CHECK-NEXT:    [[TMP4:%.*]] = zext i32 [[TMP2]] to i64
-; CHECK-NEXT:    [[TMP5:%.*]] = shl nuw i64 [[TMP4]], 32
-; CHECK-NEXT:    [[TMP6:%.*]] = or i64 [[TMP5]], [[TMP3]]
-; CHECK-NEXT:    ret i64 [[TMP6]]
+; CHECK-NEXT:    [[TMP1:%.*]] = zext i32 [[A1:%.*]] to i64
+; CHECK-NEXT:    [[TMP2:%.*]] = zext i32 [[A0:%.*]] to i64
+; CHECK-NEXT:    [[TMP3:%.*]] = shl nuw i64 [[TMP2]], 32
+; CHECK-NEXT:    [[TMP4:%.*]] = or i64 [[TMP3]], [[TMP1]]
+; CHECK-NEXT:    [[TMP5:%.*]] = call i64 @llvm.bitreverse.i64(i64 [[TMP4]])
+; CHECK-NEXT:    ret i64 [[TMP5]]
 ;
   %1 = tail call i32 @llvm.bitreverse.i32(i32 %a0)
   %2 = tail call i32 @llvm.bitreverse.i32(i32 %a1)