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Implement an important entry from README_ALTIVEC:

Browse Source 
If an altivec predicate compare is used immediately by a branch, don't
use a (serializing) MFCR instruction to read the CR6 register, which requires
a compare to get it back to CR's.  Instead, just branch on CR6 directly. :)

For example, for:
void foo2(vector float *A, vector float *B) {
  if (!vec_any_eq(*A, *B))
    *B = (vector float){0,0,0,0};
}

We now generate:

_foo2:
        mfspr r2, 256
        oris r5, r2, 12288
        mtspr 256, r5
        lvx v2, 0, r4
        lvx v3, 0, r3
        vcmpeqfp. v2, v3, v2
        bne cr6, LBB1_2 ; UnifiedReturnBlock
LBB1_1: ; cond_true
        vxor v2, v2, v2
        stvx v2, 0, r4
        mtspr 256, r2
        blr
LBB1_2: ; UnifiedReturnBlock
        mtspr 256, r2
        blr

instead of:

_foo2:
        mfspr r2, 256
        oris r5, r2, 12288
        mtspr 256, r5
        lvx v2, 0, r4
        lvx v3, 0, r3
        vcmpeqfp. v2, v3, v2
        mfcr r3, 2
        rlwinm r3, r3, 27, 31, 31
        cmpwi cr0, r3, 0
        beq cr0, LBB1_2 ; UnifiedReturnBlock
LBB1_1: ; cond_true
        vxor v2, v2, v2
        stvx v2, 0, r4
        mtspr 256, r2
        blr
LBB1_2: ; UnifiedReturnBlock
        mtspr 256, r2
        blr

This implements CodeGen/PowerPC/vec_br_cmp.ll.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@27804 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2006-04-18 17:59:36 +00:00
parent 99590420de
commit 90564f26d1
4 changed files with 106 additions and 24 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

103
lib/Target/PowerPC/PPCISelLowering.cpp
View File

@ -246,6 +246,7 @@ PPCTargetLowering::PPCTargetLowering(TargetMachine &TM)
// We have target-specific dag combine patterns for the following nodes:
setTargetDAGCombine(ISD::SINT_TO_FP);
setTargetDAGCombine(ISD::STORE);
setTargetDAGCombine(ISD::BR_CC);
computeRegisterProperties();
}
@ -1460,18 +1461,17 @@ static SDOperand LowerVECTOR_SHUFFLE(SDOperand Op, SelectionDAG &DAG) {
return DAG.getNode(PPCISD::VPERM, V1.getValueType(), V1, V2, VPermMask);
}
/// LowerINTRINSIC_WO_CHAIN - If this is an intrinsic that we want to custom
/// lower, do it, otherwise return null.
static SDOperand LowerINTRINSIC_WO_CHAIN(SDOperand Op, SelectionDAG &DAG) {
unsigned IntNo = cast<ConstantSDNode>(Op.getOperand(0))->getValue();
// If this is a lowered altivec predicate compare, CompareOpc is set to the
// opcode number of the comparison.
int CompareOpc = -1;
bool isDot = false;
switch (IntNo) {
default: return SDOperand(); // Don't custom lower most intrinsics.
// Comparison predicates.
/// getAltivecCompareInfo - Given an intrinsic, return false if it is not an
/// altivec comparison. If it is, return true and fill in Opc/isDot with
/// information about the intrinsic.
static bool getAltivecCompareInfo(SDOperand Intrin, int &CompareOpc,
bool &isDot) {
unsigned IntrinsicID = cast<ConstantSDNode>(Intrin.getOperand(0))->getValue();
CompareOpc = -1;
isDot = false;
switch (IntrinsicID) {
default: return false;
// Comparison predicates.
case Intrinsic::ppc_altivec_vcmpbfp_p: CompareOpc = 966; isDot = 1; break;
case Intrinsic::ppc_altivec_vcmpeqfp_p: CompareOpc = 198; isDot = 1; break;
case Intrinsic::ppc_altivec_vcmpequb_p: CompareOpc = 6; isDot = 1; break;
@ -1501,10 +1501,20 @@ static SDOperand LowerINTRINSIC_WO_CHAIN(SDOperand Op, SelectionDAG &DAG) {
case Intrinsic::ppc_altivec_vcmpgtuh: CompareOpc = 582; isDot = 0; break;
case Intrinsic::ppc_altivec_vcmpgtuw: CompareOpc = 646; isDot = 0; break;
}
return true;
}
/// LowerINTRINSIC_WO_CHAIN - If this is an intrinsic that we want to custom
/// lower, do it, otherwise return null.
static SDOperand LowerINTRINSIC_WO_CHAIN(SDOperand Op, SelectionDAG &DAG) {
// If this is a lowered altivec predicate compare, CompareOpc is set to the
// opcode number of the comparison.
int CompareOpc;
bool isDot;
if (!getAltivecCompareInfo(Op, CompareOpc, isDot))
return SDOperand(); // Don't custom lower most intrinsics.
assert(CompareOpc>0 && "We only lower altivec predicate compares so far!");
// If this is a non-dot comparison, make the VCMP node.
// If this is a non-dot comparison, make the VCMP node and we are done.
if (!isDot) {
SDOperand Tmp = DAG.getNode(PPCISD::VCMP, Op.getOperand(2).getValueType(),
Op.getOperand(1), Op.getOperand(2),
@ -2198,6 +2208,69 @@ SDOperand PPCTargetLowering::PerformDAGCombine(SDNode *N,
}
break;
}
case ISD::BR_CC: {
// If this is a branch on an altivec predicate comparison, lower this so
// that we don't have to do a MFCR: instead, branch directly on CR6. This
// lowering is done pre-legalize, because the legalizer lowers the predicate
// compare down to code that is difficult to reassemble.
ISD::CondCode CC = cast<CondCodeSDNode>(N->getOperand(1))->get();
SDOperand LHS = N->getOperand(2), RHS = N->getOperand(3);
int CompareOpc;
bool isDot;
if (LHS.getOpcode() == ISD::INTRINSIC_WO_CHAIN &&
isa<ConstantSDNode>(RHS) && (CC == ISD::SETEQ || CC == ISD::SETNE) &&
getAltivecCompareInfo(LHS, CompareOpc, isDot)) {
assert(isDot && "Can't compare against a vector result!");
// If this is a comparison against something other than 0/1, then we know
// that the condition is never/always true.
unsigned Val = cast<ConstantSDNode>(RHS)->getValue();
if (Val != 0 && Val != 1) {
if (CC == ISD::SETEQ) // Cond never true, remove branch.
return N->getOperand(0);
// Always !=, turn it into an unconditional branch.
return DAG.getNode(ISD::BR, MVT::Other,
N->getOperand(0), N->getOperand(4));
}
bool BranchOnWhenPredTrue = (CC == ISD::SETEQ) ^ (Val == 0);
// Create the PPCISD altivec 'dot' comparison node.
std::vector<SDOperand> Ops;
std::vector<MVT::ValueType> VTs;
Ops.push_back(LHS.getOperand(2)); // LHS of compare
Ops.push_back(LHS.getOperand(3)); // RHS of compare
Ops.push_back(DAG.getConstant(CompareOpc, MVT::i32));
VTs.push_back(LHS.getOperand(2).getValueType());
VTs.push_back(MVT::Flag);
SDOperand CompNode = DAG.getNode(PPCISD::VCMPo, VTs, Ops);
// Unpack the result based on how the target uses it.
unsigned CompOpc;
switch (cast<ConstantSDNode>(LHS.getOperand(1))->getValue()) {
default: // Can't happen, don't crash on invalid number though.
case 0: // Branch on the value of the EQ bit of CR6.
CompOpc = BranchOnWhenPredTrue ? PPC::BEQ : PPC::BNE;
break;
case 1: // Branch on the inverted value of the EQ bit of CR6.
CompOpc = BranchOnWhenPredTrue ? PPC::BNE : PPC::BEQ;
break;
case 2: // Branch on the value of the LT bit of CR6.
CompOpc = BranchOnWhenPredTrue ? PPC::BLT : PPC::BGE;
break;
case 3: // Branch on the inverted value of the LT bit of CR6.
CompOpc = BranchOnWhenPredTrue ? PPC::BGE : PPC::BLT;
break;
}
return DAG.getNode(PPCISD::COND_BRANCH, MVT::Other, N->getOperand(0),
DAG.getRegister(PPC::CR6, MVT::i32),
DAG.getConstant(CompOpc, MVT::i32),
N->getOperand(4), CompNode.getValue(1));
}
break;
}
}
return SDOperand();

9
lib/Target/PowerPC/PPCISelLowering.h
View File

@ -96,7 +96,14 @@ namespace llvm {
/// altivec VCMP*o instructions. For lack of better number, we use the
/// opcode number encoding for the OPC field to identify the compare. For
/// example, 838 is VCMPGTSH.
VCMPo
VCMPo,
/// CHAIN = COND_BRANCH CHAIN, CRRC, OPC, DESTBB [, INFLAG] - This
/// corresponds to the COND_BRANCH pseudo instruction. CRRC is the
/// condition register to branch on, OPC is the branch opcode to use (e.g.
/// PPC::BLE), DESTBB is the destination block to branch to, and INFLAG is
/// an optional input flag argument.
COND_BRANCH
};
}

12
lib/Target/PowerPC/PPCInstrInfo.td
View File

@ -34,6 +34,10 @@ def SDT_PPCvcmp : SDTypeProfile<1, 3, [
SDTCisSameAs<0, 1>, SDTCisSameAs<1, 2>, SDTCisVT<3, i32>
]>;
def SDT_PPCcondbr : SDTypeProfile<0, 3, [
SDTCisVT<1, i32>, SDTCisVT<2, OtherVT>
]>;
//===----------------------------------------------------------------------===//
// PowerPC specific DAG Nodes.
//
@ -74,6 +78,9 @@ def retflag : SDNode<"PPCISD::RET_FLAG", SDT_PPCRetFlag,
def PPCvcmp : SDNode<"PPCISD::VCMP" , SDT_PPCvcmp, []>;
def PPCvcmp_o : SDNode<"PPCISD::VCMPo", SDT_PPCvcmp, [SDNPOutFlag]>;
def PPCcondbranch : SDNode<"PPCISD::COND_BRANCH", SDT_PPCcondbr,
[SDNPHasChain, SDNPOptInFlag]>;
//===----------------------------------------------------------------------===//
// PowerPC specific transformation functions and pattern fragments.
//
@ -263,8 +270,9 @@ let Defs = [LR] in
let isBranch = 1, isTerminator = 1, hasCtrlDep = 1,
noResults = 1, PPC970_Unit = 7 in {
def COND_BRANCH : Pseudo<(ops CRRC:$crS, u16imm:$opc, target:$true),
"; COND_BRANCH", []>;
def COND_BRANCH : Pseudo<(ops CRRC:$crS, u16imm:$opc, target:$dst),
"; COND_BRANCH $crS, $opc, $dst",
[(PPCcondbranch CRRC:$crS, imm:$opc, bb:$dst)]>;
def B : IForm<18, 0, 0, (ops target:$dst),
"b $dst", BrB,
[(br bb:$dst)]>;

6
lib/Target/PowerPC/README_ALTIVEC.txt
View File

@ -53,12 +53,6 @@ of C1/C2/C3, then a load and vperm of Variable.
//===----------------------------------------------------------------------===//
Do not generate the MFCR/RLWINM sequence for predicate compares when the
predicate compare is used immediately by a branch. Just branch on the right
cond code on CR6.
//===----------------------------------------------------------------------===//
We need a way to teach tblgen that some operands of an intrinsic are required to
be constants. The verifier should enforce this constraint.