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[PATCH] Correct type used for VADD_SPLAT optimization on PowerPC

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In PPCISelLowering.cpp: PPCTargetLowering::LowerBUILD_VECTOR(), there
is an optimization for certain patterns to generate one or two vector
splats followed by a vector add or subtract.  This operation is
represented by a VADD_SPLAT in the selection DAG.  Prior to this
patch, it was possible for the VADD_SPLAT to be assigned the wrong
data type, causing incorrect code generation.  This patch corrects the
problem.

Specifically, the code previously assigned the value type of the
BUILD_VECTOR node to the newly generated VADD_SPLAT node.  This is
correct much of the time, but not always.  The problem is that the
call to isConstantSplat() may return a SplatBitSize that is not the
same as the number of bits in the original element vector type.  The
correct type to assign is a vector type with the same element bit size
as SplatBitSize.

The included test case shows an example of this, where the
BUILD_VECTOR node has a type of v16i8.  The vector to be built is {0,
16, 0, 16, 0, 16, 0, 16, 0, 16, 0, 16, 0, 16, 0, 16}.  isConstantSplat
detects that we can generate a splat of 16 for type v8i16, which is
the type we must assign to the VADD_SPLAT node.  If we do not, we
generate a vspltisb of 8 and a vaddubm, which generates the incorrect
result {16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16,
16}.  The correct code generation is a vspltish of 8 and a vadduhm.

This patch also corrected code generation for
CodeGen/PowerPC/2008-07-10-SplatMiscompile.ll, which had been marked
as an XFAIL, so we can remove the XFAIL from the test case.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@209662 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Bill Schmidt
2014-05-27 15:57:51 +00:00
parent 61e341e0bf
commit 3f01f5296e
3 changed files with 26 additions and 5 deletions
Download Patch File Download Diff File Expand all files Collapse all files
lib/Target/PowerPC/PPCISelLowering.cpp
+8 -4
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@@ -5531,10 +5531,14 @@ SDValue PPCTargetLowering::LowerBUILD_VECTOR(SDValue Op,
// we convert to a pseudo that will be expanded later into one of
// the above forms.
SDValue Elt = DAG.getConstant(SextVal, MVT::i32);
EVT VT = Op.getValueType();
int Size = VT == MVT::v16i8 ? 1 : (VT == MVT::v8i16 ? 2 : 4);
SDValue EltSize = DAG.getConstant(Size, MVT::i32);
return DAG.getNode(PPCISD::VADD_SPLAT, dl, VT, Elt, EltSize);
EVT VT = (SplatSize == 1 ? MVT::v16i8 :
(SplatSize == 2 ? MVT::v8i16 : MVT::v4i32));
SDValue EltSize = DAG.getConstant(SplatSize, MVT::i32);
SDValue RetVal = DAG.getNode(PPCISD::VADD_SPLAT, dl, VT, Elt, EltSize);
if (VT == Op.getValueType())
return RetVal;
else
return DAG.getNode(ISD::BITCAST, dl, Op.getValueType(), RetVal);
}
// If this is 0x8000_0000 x 4, turn into vspltisw + vslw. If it is