[llvm] r251740 - [X86] Reduce math for index calculation for inserting and extracting subvectors and elements by exploiting the fact that all supported vector types have a power 2 number of elements.

[Craig Topper via llvm-commits]

Author: ctopper
Date: Sat Oct 31 12:27:52 2015
New Revision: 251740

URL: http://llvm.org/viewvc/llvm-project?rev=251740&view=rev
Log:
[X86] Reduce math for index calculation for inserting and extracting subvectors and elements by exploiting the fact that all supported vector types have a power 2 number of elements.

Modified:
    llvm/trunk/lib/Target/X86/X86ISelLowering.cpp

Modified: llvm/trunk/lib/Target/X86/X86ISelLowering.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/X86/X86ISelLowering.cpp?rev=251740&r1=251739&r2=251740&view=diff
==============================================================================
--- llvm/trunk/lib/Target/X86/X86ISelLowering.cpp (original)
+++ llvm/trunk/lib/Target/X86/X86ISelLowering.cpp Sat Oct 31 12:27:52 2015
@@ -4373,19 +4373,18 @@ static SDValue ExtractSubVector(SDValue
 
   // Extract the relevant vectorWidth bits.  Generate an EXTRACT_SUBVECTOR
   unsigned ElemsPerChunk = vectorWidth / ElVT.getSizeInBits();
+  assert(isPowerOf2_32(ElemsPerChunk) && "Elements per chunk not power of 2");
 
   // This is the index of the first element of the vectorWidth-bit chunk
-  // we want.
-  unsigned NormalizedIdxVal = (((IdxVal * ElVT.getSizeInBits()) / vectorWidth)
-                               * ElemsPerChunk);
+  // we want. Since ElemsPerChunk is a power of 2 just need to clear bits.
+  IdxVal &= ~(ElemsPerChunk - 1);
 
   // If the input is a buildvector just emit a smaller one.
   if (Vec.getOpcode() == ISD::BUILD_VECTOR)
     return DAG.getNode(ISD::BUILD_VECTOR, dl, ResultVT,
-                       makeArrayRef(Vec->op_begin() + NormalizedIdxVal,
-                                    ElemsPerChunk));
+                       makeArrayRef(Vec->op_begin() + IdxVal, ElemsPerChunk));
 
-  SDValue VecIdx = DAG.getIntPtrConstant(NormalizedIdxVal, dl);
+  SDValue VecIdx = DAG.getIntPtrConstant(IdxVal, dl);
   return DAG.getNode(ISD::EXTRACT_SUBVECTOR, dl, ResultVT, Vec, VecIdx);
 }
 
@@ -4423,13 +4422,13 @@ static SDValue InsertSubVector(SDValue R
 
   // Insert the relevant vectorWidth bits.
   unsigned ElemsPerChunk = vectorWidth/ElVT.getSizeInBits();
+  assert(isPowerOf2_32(ElemsPerChunk) && "Elements per chunk not power of 2");
 
   // This is the index of the first element of the vectorWidth-bit chunk
-  // we want.
-  unsigned NormalizedIdxVal = (((IdxVal * ElVT.getSizeInBits())/vectorWidth)
-                               * ElemsPerChunk);
+  // we want. Since ElemsPerChunk is a power of 2 just need to clear bits.
+  IdxVal &= ~(ElemsPerChunk - 1);
 
-  SDValue VecIdx = DAG.getIntPtrConstant(NormalizedIdxVal, dl);
+  SDValue VecIdx = DAG.getIntPtrConstant(IdxVal, dl);
   return DAG.getNode(ISD::INSERT_SUBVECTOR, dl, ResultVT, Result, Vec, VecIdx);
 }
 
@@ -11390,10 +11389,11 @@ X86TargetLowering::LowerEXTRACT_VECTOR_E
     MVT EltVT = VecVT.getVectorElementType();
 
     unsigned ElemsPerChunk = 128 / EltVT.getSizeInBits();
+    assert(isPowerOf2_32(ElemsPerChunk) && "Elements per chunk not power of 2");
 
-    //if (IdxVal >= NumElems/2)
-    //  IdxVal -= NumElems/2;
-    IdxVal -= (IdxVal/ElemsPerChunk)*ElemsPerChunk;
+    // Find IdxVal modulo ElemsPerChunk. Since ElemsPerChunk is a power of 2
+    // this can be done with a mask.
+    IdxVal &= ElemsPerChunk - 1;
     return DAG.getNode(ISD::EXTRACT_VECTOR_ELT, dl, Op.getValueType(), Vec,
                        DAG.getConstant(IdxVal, dl, MVT::i32));
   }
@@ -11529,7 +11529,9 @@ SDValue X86TargetLowering::LowerINSERT_V
 
     // Insert the element into the desired chunk.
     unsigned NumEltsIn128 = 128 / EltVT.getSizeInBits();
-    unsigned IdxIn128 = IdxVal - (IdxVal / NumEltsIn128) * NumEltsIn128;
+    assert(isPowerOf2_32(NumEltsIn128));
+    // Since NumEltsIn128 is a power of 2 we can use mask instead of modulo.
+    unsigned IdxIn128 = IdxVal & (NumEltsIn128 - 1);
 
     V = DAG.getNode(ISD::INSERT_VECTOR_ELT, dl, V.getValueType(), V, N1,
                     DAG.getConstant(IdxIn128, dl, MVT::i32));