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DAGCombiner: Fold pointless truncate, bitcast, buildvector series

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(2xi32) (truncate ((2xi64) bitcast (buildvector i32 a, i32 x, i32 b, i32 y)))
can be folded into a (2xi32) (buildvector i32 a, i32 b).

Such a DAG would cause uneccessary vdup instructions followed by vmovn
instructions.

We generate this code on ARM NEON for a setcc olt, 2xf64, 2xf64. For example, in
the vectorized version of the code below.

double A[N];
double B[N];

void test_double_compare_to_double() {
  int i;
  for(i=0;i<N;i++)
    A[i] = (double)(A[i] < B[i]);
}

radar://13191881

Fixes bug 15283.

llvm-svn: 175670
This commit is contained in:
Arnold Schwaighofer 2013-02-20 21:33:32 +00:00
parent a0106b12e2
commit 170d2a8c25
2 changed files with 47 additions and 0 deletions
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32
lib/CodeGen/SelectionDAG/DAGCombiner.cpp
View File

@ -5361,6 +5361,38 @@ SDValue DAGCombiner::visitTRUNCATE(SDNode *N) {
}
}
// Fold a series of buildvector, bitcast, and truncate if possible.
// For example fold
// (2xi32 trunc (bitcast ((4xi32)buildvector x, x, y, y) 2xi64)) to
// (2xi32 (buildvector x, y)).
if (Level == AfterLegalizeVectorOps && VT.isVector() &&
N0.getOpcode() == ISD::BITCAST && N0.hasOneUse() &&
N0.getOperand(0).getOpcode() == ISD::BUILD_VECTOR &&
N0.getOperand(0).hasOneUse()) {
SDValue BuildVect = N0.getOperand(0);
EVT BuildVectEltTy = BuildVect.getValueType().getVectorElementType();
EVT TruncVecEltTy = VT.getVectorElementType();
// Check that the element types match.
if (BuildVectEltTy == TruncVecEltTy) {
// Now we only need to compute the offset of the truncated elements.
unsigned BuildVecNumElts = BuildVect.getNumOperands();
unsigned TruncVecNumElts = VT.getVectorNumElements();
unsigned TruncEltOffset = BuildVecNumElts / TruncVecNumElts;
assert((BuildVecNumElts % TruncVecNumElts) == 0 &&
"Invalid number of elements");
SmallVector<SDValue, 8> Opnds;
for (unsigned i = 0, e = BuildVecNumElts; i != e; i += TruncEltOffset)
Opnds.push_back(BuildVect.getOperand(i));
return DAG.getNode(ISD::BUILD_VECTOR, N->getDebugLoc(), VT, &Opnds[0],
Opnds.size());
}
}
// See if we can simplify the input to this truncate through knowledge that
// only the low bits are being used.
// For example "trunc (or (shl x, 8), y)" // -> trunc y

15
test/CodeGen/ARM/neon_cmp.ll Normal file
View File

@ -0,0 +1,15 @@
; RUN: llc < %s -march=arm -mcpu=cortex-a9 | FileCheck %s
; bug 15283
; radar://13191881
; CHECK: vfcmp
define void @vfcmp(<2 x double>* %a, <2 x double>* %b) {
%wide.load = load <2 x double>* %a, align 4
%wide.load2 = load <2 x double>* %b, align 4
; CHECK-NOT: vdup.32
; CHECK-NOT: vmovn.i64
%v1 = fcmp olt <2 x double> %wide.load, %wide.load2
%v2 = zext <2 x i1> %v1 to <2 x i32>
%v3 = sitofp <2 x i32> %v2 to <2 x double>
store <2 x double> %v3, <2 x double>* %b, align 4
ret void
}