[llvm] r298108 - [SelectionDAG] Add SelectionDAG.computeKnownBits test support for ISD::ABS

[Simon Pilgrim via llvm-commits]

Author: rksimon
Date: Fri Mar 17 12:45:36 2017
New Revision: 298108

URL: http://llvm.org/viewvc/llvm-project?rev=298108&view=rev
Log:
[SelectionDAG] Add SelectionDAG.computeKnownBits test support for ISD::ABS

Modified:
    llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
    llvm/trunk/test/CodeGen/X86/known-bits-vector.ll

Modified: llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAG.cpp?rev=298108&r1=298107&r2=298108&view=diff
==============================================================================
--- llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAG.cpp (original)
+++ llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAG.cpp Fri Mar 17 12:45:36 2017
@@ -2730,6 +2730,26 @@ void SelectionDAG::computeKnownBits(SDVa
     KnownOne = KnownOne2.byteSwap();
     break;
   }
+  case ISD::ABS: {
+    computeKnownBits(Op.getOperand(0), KnownZero2, KnownOne2, DemandedElts,
+                     Depth + 1);
+
+    // If the source's MSB is zero then we know the rest of the bits already.
+    if (KnownZero2[BitWidth - 1]) {
+      KnownZero = KnownZero2;
+      KnownOne = KnownOne2;
+      break;
+    }
+
+    // We only know that the absolute values's MSB will be zero iff there is
+    // a set bit that isn't the sign bit (otherwise it could be INT_MIN).
+    KnownOne2.clearBit(BitWidth - 1);
+    if (KnownOne2.getBoolValue()) {
+      KnownZero = APInt::getSignBit(BitWidth);
+      break;
+    }
+    break;
+  }
   case ISD::UMIN: {
     computeKnownBits(Op.getOperand(0), KnownZero, KnownOne, DemandedElts,
                      Depth + 1);

Modified: llvm/trunk/test/CodeGen/X86/known-bits-vector.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/X86/known-bits-vector.ll?rev=298108&r1=298107&r2=298108&view=diff
==============================================================================
--- llvm/trunk/test/CodeGen/X86/known-bits-vector.ll (original)
+++ llvm/trunk/test/CodeGen/X86/known-bits-vector.ll Fri Mar 17 12:45:36 2017
@@ -590,11 +590,7 @@ define <4 x float> @knownbits_or_abs_uit
 ; X32-NEXT:    vpor {{\.LCPI.*}}, %xmm0, %xmm0
 ; X32-NEXT:    vpshufd {{.*#+}} xmm0 = xmm0[0,2,0,2]
 ; X32-NEXT:    vpabsd %xmm0, %xmm0
-; X32-NEXT:    vpblendw {{.*#+}} xmm1 = xmm0[0],mem[1],xmm0[2],mem[3],xmm0[4],mem[5],xmm0[6],mem[7]
-; X32-NEXT:    vpsrld $16, %xmm0, %xmm0
-; X32-NEXT:    vpblendw {{.*#+}} xmm0 = xmm0[0],mem[1],xmm0[2],mem[3],xmm0[4],mem[5],xmm0[6],mem[7]
-; X32-NEXT:    vaddps {{\.LCPI.*}}, %xmm0, %xmm0
-; X32-NEXT:    vaddps %xmm0, %xmm1, %xmm0
+; X32-NEXT:    vcvtdq2ps %xmm0, %xmm0
 ; X32-NEXT:    retl
 ;
 ; X64-LABEL: knownbits_or_abs_uitofp:
@@ -602,11 +598,7 @@ define <4 x float> @knownbits_or_abs_uit
 ; X64-NEXT:    vpor {{.*}}(%rip), %xmm0, %xmm0
 ; X64-NEXT:    vpshufd {{.*#+}} xmm0 = xmm0[0,2,0,2]
 ; X64-NEXT:    vpabsd %xmm0, %xmm0
-; X64-NEXT:    vpblendw {{.*#+}} xmm1 = xmm0[0],mem[1],xmm0[2],mem[3],xmm0[4],mem[5],xmm0[6],mem[7]
-; X64-NEXT:    vpsrld $16, %xmm0, %xmm0
-; X64-NEXT:    vpblendw {{.*#+}} xmm0 = xmm0[0],mem[1],xmm0[2],mem[3],xmm0[4],mem[5],xmm0[6],mem[7]
-; X64-NEXT:    vaddps {{.*}}(%rip), %xmm0, %xmm0
-; X64-NEXT:    vaddps %xmm0, %xmm1, %xmm0
+; X64-NEXT:    vcvtdq2ps %xmm0, %xmm0
 ; X64-NEXT:    retq
   %1 = or <4 x i32> %a0, <i32 1, i32 0, i32 3, i32 0>
   %2 = shufflevector <4 x i32> %1, <4 x i32> undef, <4 x i32> <i32 0, i32 2, i32 0, i32 2>