Revert "[ISel] Match all bits when merge undef(s) for DAG combine"

This reverts commit 5fe5aa284e.

llvm/include/llvm/ADT/APInt.h

@@ -2239,16 +2239,12 @@ Optional<unsigned> GetMostSignificantDifferentBit(const APInt &A,
 /// Splat/Merge neighboring bits to widen/narrow the bitmask represented
 /// by \param A to \param NewBitWidth bits.
 ///
-/// MatchAnyBits: (Default)
 /// e.g. ScaleBitMask(0b0101, 8) -> 0b00110011
 /// e.g. ScaleBitMask(0b00011011, 4) -> 0b0111
-///
-/// MatchAllBits:
-/// e.g. ScaleBitMask(0b0101, 8) -> 0b00110011
-/// e.g. ScaleBitMask(0b00011011, 4) -> 0b0001
 /// A.getBitwidth() or NewBitWidth must be a whole multiples of the other.
-APInt ScaleBitMask(const APInt &A, unsigned NewBitWidth,
+///
-                   bool MatchAllBits = false);
+/// TODO: Do we need a mode where all bits must be set when merging down?
+APInt ScaleBitMask(const APInt &A, unsigned NewBitWidth);
 } // namespace APIntOps
 
 // See friend declaration above. This additional declaration is required in

llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp

@@ -2712,16 +2712,7 @@ bool SelectionDAG::isSplatValue(SDValue V, const APInt &DemandedElts,
         SubDemandedElts &= ScaledDemandedElts;
         if (!isSplatValue(Src, SubDemandedElts, SubUndefElts, Depth + 1))
           return false;
-
+        UndefElts |= APIntOps::ScaleBitMask(SubUndefElts, NumElts);
-        // Here we can't do "MatchAnyBits" operation merge for undef bits.
-        // Because some operation only use part value of the source.
-        // Take llvm.fshl.* for example:
-        // t1: v4i32 = Constant:i32<12>, undef:i32, Constant:i32<12>, undef:i32
-        // t2: v2i64 = bitcast t1
-        // t5: v2i64 = fshl t3, t4, t2
-        // We can not convert t2 to {i64 undef, i64 undef}
-        UndefElts |= APIntOps::ScaleBitMask(SubUndefElts, NumElts,
-                                            /*MatchAllBits=*/true);
       }
       return true;
     }

llvm/lib/Support/APInt.cpp

@@ -2968,8 +2968,7 @@ llvm::APIntOps::GetMostSignificantDifferentBit(const APInt &A, const APInt &B) {
   return A.getBitWidth() - ((A ^ B).countLeadingZeros() + 1);
 }
 
-APInt llvm::APIntOps::ScaleBitMask(const APInt &A, unsigned NewBitWidth,
+APInt llvm::APIntOps::ScaleBitMask(const APInt &A, unsigned NewBitWidth) {
-                                   bool MatchAllBits) {
   unsigned OldBitWidth = A.getBitWidth();
   assert((((OldBitWidth % NewBitWidth) == 0) ||
           ((NewBitWidth % OldBitWidth) == 0)) &&
@@ -2993,16 +2992,11 @@ APInt llvm::APIntOps::ScaleBitMask(const APInt &A, unsigned NewBitWidth,
       if (A[i])
         NewA.setBits(i * Scale, (i + 1) * Scale);
   } else {
+    // Merge bits - if any old bit is set, then set scale equivalent new bit.
     unsigned Scale = OldBitWidth / NewBitWidth;
-    for (unsigned i = 0; i != NewBitWidth; ++i) {
+    for (unsigned i = 0; i != NewBitWidth; ++i)
-      if (MatchAllBits) {
+      if (!A.extractBits(Scale, i * Scale).isZero())
-        if (A.extractBits(Scale, i * Scale).isAllOnes())
+        NewA.setBit(i);
-          NewA.setBit(i);
-      } else {
-        if (!A.extractBits(Scale, i * Scale).isZero())
-          NewA.setBit(i);
-      }
-    }
   }
 
   return NewA;

llvm/test/CodeGen/X86/fshl-splat-undef.ll

@@ -20,14 +20,8 @@
 define void @test_fshl(<8 x i64> %lo, <8 x i64> %hi, <8 x i64>* %arr) {
 ; CHECK-LABEL: test_fshl:
 ; CHECK:       # %bb.0: # %entry
-; CHECK-NEXT:    movl $63, %eax
-; CHECK-NEXT:    vmovd %eax, %xmm2
-; CHECK-NEXT:    movl $12, %eax
-; CHECK-NEXT:    vmovd %eax, %xmm3
-; CHECK-NEXT:    vpand %xmm2, %xmm3, %xmm2
-; CHECK-NEXT:    vpsllq %xmm2, %zmm1, %zmm1
 ; CHECK-NEXT:    movl {{[0-9]+}}(%esp), %eax
-; CHECK-NEXT:    vpsrlq $52, %zmm0, %zmm0
+; CHECK-NEXT:    vpsrlq $1, %zmm0, %zmm0
 ; CHECK-NEXT:    vpternlogq $168, {{\.?LCPI[0-9]+_[0-9]+}}, %zmm1, %zmm0
 ; CHECK-NEXT:    vmovdqa64 %zmm0, (%eax)
 ; CHECK-NEXT:    vzeroupper

llvm/unittests/ADT/APIntTest.cpp

@@ -3115,15 +3115,6 @@ TEST(APIntTest, ScaleBitMask) {
             APInt::getAllOnes(256));
   EXPECT_EQ(APIntOps::ScaleBitMask(APInt::getOneBitSet(4096, 32), 256),
             APInt::getOneBitSet(256, 2));
-
-  EXPECT_EQ(APIntOps::ScaleBitMask(APInt(2, 0x00), 8, true), APInt(8, 0x00));
-  EXPECT_EQ(APIntOps::ScaleBitMask(APInt(2, 0x01), 8, true), APInt(8, 0x0F));
-  EXPECT_EQ(APIntOps::ScaleBitMask(APInt(2, 0x02), 8, true), APInt(8, 0xF0));
-  EXPECT_EQ(APIntOps::ScaleBitMask(APInt(2, 0x03), 8, true), APInt(8, 0xFF));
-
-  EXPECT_EQ(APIntOps::ScaleBitMask(APInt(8, 0x00), 4, true), APInt(4, 0x00));
-  EXPECT_EQ(APIntOps::ScaleBitMask(APInt(8, 0xFF), 4, true), APInt(4, 0x0F));
-  EXPECT_EQ(APIntOps::ScaleBitMask(APInt(8, 0xE4), 4, true), APInt(4, 0x08));
 }
 
 } // end anonymous namespace