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[PowerPC] Handle cmp op promotion for SELECT[_CC] nodes in PPCTL::DAGCombineExtBoolTrunc 

PPCTargetLowering::DAGCombineExtBoolTrunc contains logic to remove unwanted
truncations and extensions when dealing with nodes of the form:
  zext(binary-ops(binary-ops(trunc(x), trunc(y)), ...)

There was a FIXME in the implementation (now removed) regarding the fact that
the function would abort the transformations if any of the non-output operands
of a SELECT or SELECT_CC node would need to be promoted (because they were
also output operands, for example). As a result, we continued to generate
unnecessary zero-extends for code such as this:

  unsigned foo(unsigned a, unsigned b) {
    return  (a <= b) ? a : b;
  }

which would produce:

  cmplw 0, 3, 4
  isel 3, 4, 3, 1
  rldicl 3, 3, 0, 32
  blr

and now we produce:

  cmplw 0, 3, 4
  isel 3, 4, 3, 1
  blr

which is better in the obvious way.

llvm-svn: 224213
This commit is contained in:
Hal Finkel 2014-12-14 05:53:19 +00:00
parent 0215c88f00
commit 4104a1a346
2 changed files with 60 additions and 18 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

67
llvm/lib/Target/PowerPC/PPCISelLowering.cpp
View File

@ -8127,6 +8127,10 @@ SDValue PPCTargetLowering::DAGCombineExtBoolTrunc(SDNode *N,
}
}
// The operands of a select that must be truncated when the select is
// promoted because the operand is actually part of the to-be-promoted set.
DenseMap<SDNode *, EVT> SelectTruncOp[2];
// Make sure that this is a self-contained cluster of operations (which
// is not quite the same thing as saying that everything has only one
// use).
@ -8141,18 +8145,19 @@ SDValue PPCTargetLowering::DAGCombineExtBoolTrunc(SDNode *N,
if (User != N && !Visited.count(User))
return SDValue();
// Make sure that we're not going to promote the non-output-value
// operand(s) or SELECT or SELECT_CC.
// FIXME: Although we could sometimes handle this, and it does occur in
// practice that one of the condition inputs to the select is also one of
// the outputs, we currently can't deal with this.
// If we're going to promote the non-output-value operand(s) or SELECT or
// SELECT_CC, record them for truncation.
if (User->getOpcode() == ISD::SELECT) {
if (User->getOperand(0) == Inputs[i])
return SDValue();
SelectTruncOp[0].insert(std::make_pair(User,
User->getOperand(0).getValueType()));
} else if (User->getOpcode() == ISD::SELECT_CC) {
if (User->getOperand(0) == Inputs[i] ||
User->getOperand(1) == Inputs[i])
return SDValue();
if (User->getOperand(0) == Inputs[i])
SelectTruncOp[0].insert(std::make_pair(User,
User->getOperand(0).getValueType()));
if (User->getOperand(1) == Inputs[i])
SelectTruncOp[1].insert(std::make_pair(User,
User->getOperand(1).getValueType()));
}
}
}
@ -8165,18 +8170,19 @@ SDValue PPCTargetLowering::DAGCombineExtBoolTrunc(SDNode *N,
if (User != N && !Visited.count(User))
return SDValue();
// Make sure that we're not going to promote the non-output-value
// operand(s) or SELECT or SELECT_CC.
// FIXME: Although we could sometimes handle this, and it does occur in
// practice that one of the condition inputs to the select is also one of
// the outputs, we currently can't deal with this.
// If we're going to promote the non-output-value operand(s) or SELECT or
// SELECT_CC, record them for truncation.
if (User->getOpcode() == ISD::SELECT) {
if (User->getOperand(0) == PromOps[i])
return SDValue();
SelectTruncOp[0].insert(std::make_pair(User,
User->getOperand(0).getValueType()));
} else if (User->getOpcode() == ISD::SELECT_CC) {
if (User->getOperand(0) == PromOps[i] ||
User->getOperand(1) == PromOps[i])
return SDValue();
if (User->getOperand(0) == PromOps[i])
SelectTruncOp[0].insert(std::make_pair(User,
User->getOperand(0).getValueType()));
if (User->getOperand(1) == PromOps[i])
SelectTruncOp[1].insert(std::make_pair(User,
User->getOperand(1).getValueType()));
}
}
}
@ -8257,6 +8263,19 @@ SDValue PPCTargetLowering::DAGCombineExtBoolTrunc(SDNode *N,
continue;
}
// For SELECT and SELECT_CC nodes, we do a similar check for any
// to-be-promoted comparison inputs.
if (PromOp.getOpcode() == ISD::SELECT ||
PromOp.getOpcode() == ISD::SELECT_CC) {
if ((SelectTruncOp[0].count(PromOp.getNode()) &&
PromOp.getOperand(0).getValueType() != N->getValueType(0)) ||
(SelectTruncOp[1].count(PromOp.getNode()) &&
PromOp.getOperand(1).getValueType() != N->getValueType(0))) {
PromOps.insert(PromOps.begin(), PromOp);
continue;
}
}
SmallVector<SDValue, 3> Ops(PromOp.getNode()->op_begin(),
PromOp.getNode()->op_end());
@ -8275,6 +8294,18 @@ SDValue PPCTargetLowering::DAGCombineExtBoolTrunc(SDNode *N,
Ops[C+i] = DAG.getAnyExtOrTrunc(Ops[C+i], dl, N->getValueType(0));
}
// If we've promoted the comparison inputs of a SELECT or SELECT_CC,
// truncate them again to the original value type.
if (PromOp.getOpcode() == ISD::SELECT ||
PromOp.getOpcode() == ISD::SELECT_CC) {
auto SI0 = SelectTruncOp[0].find(PromOp.getNode());
if (SI0 != SelectTruncOp[0].end())
Ops[0] = DAG.getNode(ISD::TRUNCATE, dl, SI0->second, Ops[0]);
auto SI1 = SelectTruncOp[1].find(PromOp.getNode());
if (SI1 != SelectTruncOp[1].end())
Ops[1] = DAG.getNode(ISD::TRUNCATE, dl, SI1->second, Ops[1]);
}
DAG.ReplaceAllUsesOfValueWith(PromOp,
DAG.getNode(PromOp.getOpcode(), dl, N->getValueType(0), Ops));
}

11
llvm/test/CodeGen/PowerPC/rm-zext.ll
View File

@ -28,5 +28,16 @@ entry:
; CHECK: blr
}
define zeroext i32 @min(i32 zeroext %a, i32 zeroext %b) #0 {
entry:
%cmp = icmp ule i32 %a, %b
%cond = select i1 %cmp, i32 %a, i32 %b
ret i32 %cond
; CHECK-LABEL @min
; CHECK-NOT: rldicl 3, {{[0-9]+}}, 0, 32
; CHECK: blr
}
attributes #0 = { nounwind readnone }