Revert "[ValueTracking] Improve Bitcast handling to match SDAG" (#145191)

Reverts llvm/llvm-project#125935

Causes miscompiles, see comments in #125935

Author: aeubanks

llvm/lib/Analysis/ValueTracking.cpp

@@ -1346,8 +1346,6 @@ static void computeKnownBitsFromOperator(const Operator *I,
         isa<ScalableVectorType>(I->getType()))
       break;
 
-    unsigned NumElts = DemandedElts.getBitWidth();
-    bool IsLE = Q.DL.isLittleEndian();
     // Look through a cast from narrow vector elements to wider type.
     // Examples: v4i32 -> v2i64, v3i8 -> v24
     unsigned SubBitWidth = SrcVecTy->getScalarSizeInBits();
@@ -1366,6 +1364,7 @@ static void computeKnownBitsFromOperator(const Operator *I,
       //
       // The known bits of each sub-element are then inserted into place
       // (dependent on endian) to form the full result of known bits.
+      unsigned NumElts = DemandedElts.getBitWidth();
       unsigned SubScale = BitWidth / SubBitWidth;
       APInt SubDemandedElts = APInt::getZero(NumElts * SubScale);
       for (unsigned i = 0; i != NumElts; ++i) {
@@ -1377,32 +1376,10 @@ static void computeKnownBitsFromOperator(const Operator *I,
       for (unsigned i = 0; i != SubScale; ++i) {
         computeKnownBits(I->getOperand(0), SubDemandedElts.shl(i), KnownSrc, Q,
                          Depth + 1);
-        unsigned ShiftElt = IsLE ? i : SubScale - 1 - i;
+        unsigned ShiftElt = Q.DL.isLittleEndian() ? i : SubScale - 1 - i;
         Known.insertBits(KnownSrc, ShiftElt * SubBitWidth);
       }
     }
-    // Look through a cast from wider vector elements to narrow type.
-    // Examples: v2i64 -> v4i32
-    if (SubBitWidth % BitWidth == 0) {
-      unsigned SubScale = SubBitWidth / BitWidth;
-      KnownBits KnownSrc(SubBitWidth);
-      APInt SubDemandedElts =
-          APIntOps::ScaleBitMask(DemandedElts, NumElts / SubScale);
-      computeKnownBits(I->getOperand(0), SubDemandedElts, KnownSrc, Q,
-                       Depth + 1);
-
-      Known.Zero.setAllBits();
-      Known.One.setAllBits();
-      for (unsigned i = 0; i != SubScale; ++i) {
-        if (DemandedElts[i]) {
-          unsigned Shifts = IsLE ? i : NumElts - 1 - i;
-          unsigned Offset = (Shifts % SubScale) * BitWidth;
-          Known = Known.intersectWith(KnownSrc.extractBits(BitWidth, Offset));
-          if (Known.isUnknown())
-            break;
-        }
-      }
-    }
     break;
   }
   case Instruction::SExt: {

llvm/test/Transforms/InstCombine/X86/x86-vector-shifts.ll

@@ -3732,6 +3732,7 @@ define <4 x i64> @test_avx2_psrl_0() {
   ret <4 x i64> %16
 }
 
+; FIXME: Failure to peek through bitcasts to ensure psllq shift amount is within bounds.
 define <2 x i64> @PR125228(<2 x i64> %v, <2 x i64> %s) {
 ; CHECK-LABEL: @PR125228(
 ; CHECK-NEXT:    [[MASK:%.*]] = and <2 x i64> [[S:%.*]], splat (i64 63)
@@ -3740,8 +3741,7 @@ define <2 x i64> @PR125228(<2 x i64> %v, <2 x i64> %s) {
 ; CHECK-NEXT:    [[CAST:%.*]] = bitcast <2 x i64> [[MASK]] to <16 x i8>
 ; CHECK-NEXT:    [[PSRLDQ:%.*]] = shufflevector <16 x i8> [[CAST]], <16 x i8> poison, <16 x i32> <i32 8, i32 9, i32 10, i32 11, i32 12, i32 13, i32 14, i32 15, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison>
 ; CHECK-NEXT:    [[CAST3:%.*]] = bitcast <16 x i8> [[PSRLDQ]] to <2 x i64>
-; CHECK-NEXT:    [[TMP2:%.*]] = shufflevector <2 x i64> [[CAST3]], <2 x i64> poison, <2 x i32> zeroinitializer
-; CHECK-NEXT:    [[SLL1:%.*]] = shl <2 x i64> [[V]], [[TMP2]]
+; CHECK-NEXT:    [[SLL1:%.*]] = call <2 x i64> @llvm.x86.sse2.psll.q(<2 x i64> [[V]], <2 x i64> [[CAST3]])
 ; CHECK-NEXT:    [[SHUFP_UNCASTED:%.*]] = shufflevector <2 x i64> [[SLL0]], <2 x i64> [[SLL1]], <2 x i32> <i32 0, i32 3>
 ; CHECK-NEXT:    ret <2 x i64> [[SHUFP_UNCASTED]]
 ;

llvm/test/Transforms/InstCombine/bitcast-known-bits.ll

@@ -12,7 +12,8 @@ define <16 x i8> @knownbits_bitcast_masked_shift(<16 x i8> %arg1, <16 x i8> %arg
 ; CHECK-NEXT:    [[BITCAST4:%.*]] = bitcast <16 x i8> [[OR]] to <8 x i16>
 ; CHECK-NEXT:    [[SHL5:%.*]] = shl nuw <8 x i16> [[BITCAST4]], splat (i16 2)
 ; CHECK-NEXT:    [[BITCAST6:%.*]] = bitcast <8 x i16> [[SHL5]] to <16 x i8>
-; CHECK-NEXT:    ret <16 x i8> [[BITCAST6]]
+; CHECK-NEXT:    [[AND7:%.*]] = and <16 x i8> [[BITCAST6]], splat (i8 -52)
+; CHECK-NEXT:    ret <16 x i8> [[AND7]]
 ;
   %and = and <16 x i8> %arg1, splat (i8 3)
   %and3 = and <16 x i8> %arg2, splat (i8 48)
@@ -32,7 +33,8 @@ define <16 x i8> @knownbits_shuffle_masked_nibble_shift(<16 x i8> %arg)  {
 ; CHECK-NEXT:    [[BITCAST1:%.*]] = bitcast <16 x i8> [[SHUFFLEVECTOR]] to <8 x i16>
 ; CHECK-NEXT:    [[SHL:%.*]] = shl nuw <8 x i16> [[BITCAST1]], splat (i16 4)
 ; CHECK-NEXT:    [[BITCAST2:%.*]] = bitcast <8 x i16> [[SHL]] to <16 x i8>
-; CHECK-NEXT:    ret <16 x i8> [[BITCAST2]]
+; CHECK-NEXT:    [[AND3:%.*]] = and <16 x i8> [[BITCAST2]], splat (i8 -16)
+; CHECK-NEXT:    ret <16 x i8> [[AND3]]
 ;
   %and = and <16 x i8> %arg, splat (i8 15)
   %shufflevector = shufflevector <16 x i8> %and, <16 x i8> poison, <16 x i32> <i32 1, i32 0, i32 3, i32 2, i32 5, i32 4, i32 7, i32 6, i32 9, i32 8, i32 11, i32 10, i32 13, i32 12, i32 15, i32 14>
@@ -51,7 +53,8 @@ define <16 x i8> @knownbits_reverse_shuffle_masked_shift(<16 x i8> %arg)  {
 ; CHECK-NEXT:    [[BITCAST1:%.*]] = bitcast <16 x i8> [[SHUFFLEVECTOR]] to <8 x i16>
 ; CHECK-NEXT:    [[SHL:%.*]] = shl nuw <8 x i16> [[BITCAST1]], splat (i16 4)
 ; CHECK-NEXT:    [[BITCAST2:%.*]] = bitcast <8 x i16> [[SHL]] to <16 x i8>
-; CHECK-NEXT:    ret <16 x i8> [[BITCAST2]]
+; CHECK-NEXT:    [[AND3:%.*]] = and <16 x i8> [[BITCAST2]], splat (i8 -16)
+; CHECK-NEXT:    ret <16 x i8> [[AND3]]
 ;
   %and = and <16 x i8> %arg, splat (i8 15)
   %shufflevector = shufflevector <16 x i8> %and, <16 x i8> poison, <16 x i32> <i32 3, i32 2, i32 1, i32 0, i32 7, i32 6, i32 5, i32 4, i32 11, i32 10, i32 9, i32 8, i32 15, i32 14, i32 13, i32 12>
@@ -67,7 +70,8 @@ define <16 x i8> @knownbits_extract_bit(<8 x i16> %arg)  {
 ; CHECK-SAME: <8 x i16> [[ARG:%.*]]) {
 ; CHECK-NEXT:    [[LSHR:%.*]] = lshr <8 x i16> [[ARG]], splat (i16 15)
 ; CHECK-NEXT:    [[BITCAST1:%.*]] = bitcast <8 x i16> [[LSHR]] to <16 x i8>
-; CHECK-NEXT:    ret <16 x i8> [[BITCAST1]]
+; CHECK-NEXT:    [[AND:%.*]] = and <16 x i8> [[BITCAST1]], splat (i8 1)
+; CHECK-NEXT:    ret <16 x i8> [[AND]]
 ;
   %lshr = lshr <8 x i16> %arg, splat (i16 15)
   %bitcast1 = bitcast <8 x i16> %lshr to <16 x i8>
@@ -84,8 +88,7 @@ define { i32, i1 } @knownbits_popcount_add_with_overflow(<2 x i64> %arg1, <2 x i
 ; CHECK-NEXT:    [[CALL9:%.*]] = tail call range(i64 0, 65) <2 x i64> @llvm.ctpop.v2i64(<2 x i64> [[ARG2]])
 ; CHECK-NEXT:    [[BITCAST10:%.*]] = bitcast <2 x i64> [[CALL9]] to <4 x i32>
 ; CHECK-NEXT:    [[EXTRACTELEMENT11:%.*]] = extractelement <4 x i32> [[BITCAST10]], i64 0
-; CHECK-NEXT:    [[CALL12:%.*]] = add nuw nsw i32 [[EXTRACTELEMENT]], [[EXTRACTELEMENT11]]
-; CHECK-NEXT:    [[TMP1:%.*]] = insertvalue { i32, i1 } { i32 poison, i1 false }, i32 [[CALL12]], 0
+; CHECK-NEXT:    [[TMP1:%.*]] = tail call { i32, i1 } @llvm.uadd.with.overflow.i32(i32 [[EXTRACTELEMENT]], i32 [[EXTRACTELEMENT11]])
 ; CHECK-NEXT:    ret { i32, i1 } [[TMP1]]
 ;
   %call = tail call <2 x i64> @llvm.ctpop.v2i64(<2 x i64> %arg1)
@@ -107,7 +110,11 @@ define <16 x i8> @knownbits_shuffle_add_shift_v32i8(<16 x i8> %arg1, <8 x i16> %
 ; CHECK-NEXT:    [[BITCAST11:%.*]] = bitcast <8 x i16> [[SHL10]] to <16 x i8>
 ; CHECK-NEXT:    [[ADD12:%.*]] = add <16 x i8> [[BITCAST11]], [[BITCAST7]]
 ; CHECK-NEXT:    [[ADD14:%.*]] = add <16 x i8> [[ADD12]], [[ARG1]]
-; CHECK-NEXT:    ret <16 x i8> [[ADD14]]
+; CHECK-NEXT:    [[BITCAST14:%.*]] = bitcast <16 x i8> [[ADD12]] to <8 x i16>
+; CHECK-NEXT:    [[SHL15:%.*]] = shl <8 x i16> [[BITCAST14]], splat (i16 8)
+; CHECK-NEXT:    [[BITCAST16:%.*]] = bitcast <8 x i16> [[SHL15]] to <16 x i8>
+; CHECK-NEXT:    [[ADD13:%.*]] = add <16 x i8> [[ADD14]], [[BITCAST16]]
+; CHECK-NEXT:    ret <16 x i8> [[ADD13]]
 ;
   %shl6 = shl <8 x i16> %arg2, splat (i16 8)
   %bitcast7 = bitcast <8 x i16> %shl6 to <16 x i8>