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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.

llvm-svn: 209662
This commit is contained in:
Bill Schmidt 2014-05-27 15:57:51 +00:00
parent 62d7aed204
commit b806d02b5b
3 changed files with 26 additions and 5 deletions
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12
lib/Target/PowerPC/PPCISelLowering.cpp
View File

@ -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

1
test/CodeGen/PowerPC/2008-07-10-SplatMiscompile.ll
View File

@ -1,6 +1,5 @@
; RUN: llc < %s -march=ppc32 -mcpu=g5 | grep vadduhm
; RUN: llc < %s -march=ppc32 -mcpu=g5 | grep vsubuhm
; XFAIL: *
define <4 x i32> @test() nounwind {
ret <4 x i32> < i32 4293066722, i32 4293066722, i32 4293066722, i32 4293066722>

18
test/CodeGen/PowerPC/splat-bug.ll Normal file
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@ -0,0 +1,18 @@
; RUN: llc -mcpu=ppc64 -O0 -fast-isel=false < %s | FileCheck %s
; Checks for a previous bug where vspltisb/vaddubm were issued in place
; of vsplitsh/vadduhm.
target datalayout = "E-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v128:128:128-n32:64"
target triple = "powerpc64-unknown-linux-gnu"
@a = external global <16 x i8>
define void @foo() nounwind ssp {
; CHECK: foo:
store <16 x i8> <i8 0, i8 16, i8 0, i8 16, i8 0, i8 16, i8 0, i8 16, i8 0, i8 16, i8 0, i8 16, i8 0, i8 16, i8 0, i8 16>, <16 x i8>* @a
; CHECK: vspltish [[REG:[0-9]+]], 8
; CHECK: vadduhm {{[0-9]+}}, [[REG]], [[REG]]
ret void
}