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[SelectionDAG] swap select_cc operands to enable folding 

The DAGCombiner tries to SimplifySelectCC as follows:

  select_cc(x, y, 16, 0, cc) -> shl(zext(set_cc(x, y, cc)), 4)

It can't cope with the situation of reordered operands:

  select_cc(x, y, 0, 16, cc)

In that case we just need to swap the operands and invert the Condition Code:

  select_cc(x, y, 16, 0, ~cc)

Differential Revision: https://reviews.llvm.org/D53236

llvm-svn: 346484
This commit is contained in:
Alexandros Lamprineas 2018-11-09 11:09:40 +00:00
parent 52578f95c9
commit e15c982f6d
3 changed files with 95 additions and 45 deletions
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70
llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
View File

@ -18173,6 +18173,7 @@ SDValue DAGCombiner::SimplifySelectCC(const SDLoc &DL, SDValue N0, SDValue N1,
EVT VT = N2.getValueType();
ConstantSDNode *N1C = dyn_cast<ConstantSDNode>(N1.getNode());
ConstantSDNode *N2C = dyn_cast<ConstantSDNode>(N2.getNode());
ConstantSDNode *N3C = dyn_cast<ConstantSDNode>(N3.getNode());
// Determine if the condition we're dealing with is constant
SDValue SCC = SimplifySetCC(getSetCCResultType(N0.getValueType()),
@ -18273,48 +18274,49 @@ SDValue DAGCombiner::SimplifySelectCC(const SDLoc &DL, SDValue N0, SDValue N1,
}
// fold select C, 16, 0 -> shl C, 4
if (N2C && isNullConstant(N3) && N2C->getAPIntValue().isPowerOf2() &&
bool Fold = N2C && isNullConstant(N3) && N2C->getAPIntValue().isPowerOf2();
bool Swap = N3C && isNullConstant(N2) && N3C->getAPIntValue().isPowerOf2();
if ((Fold || Swap) &&
TLI.getBooleanContents(N0.getValueType()) ==
TargetLowering::ZeroOrOneBooleanContent) {
TargetLowering::ZeroOrOneBooleanContent &&
(!LegalOperations ||
TLI.isOperationLegal(ISD::SETCC, N0.getValueType()))) {
if (Swap) {
CC = ISD::getSetCCInverse(CC, N0.getValueType().isInteger());
std::swap(N2C, N3C);
}
// If the caller doesn't want us to simplify this into a zext of a compare,
// don't do it.
if (NotExtCompare && N2C->isOne())
return SDValue();
// Get a SetCC of the condition
// NOTE: Don't create a SETCC if it's not legal on this target.
if (!LegalOperations ||
TLI.isOperationLegal(ISD::SETCC, N0.getValueType())) {
SDValue Temp, SCC;
// cast from setcc result type to select result type
if (LegalTypes) {
SCC = DAG.getSetCC(DL, getSetCCResultType(N0.getValueType()),
N0, N1, CC);
if (N2.getValueType().bitsLT(SCC.getValueType()))
Temp = DAG.getZeroExtendInReg(SCC, SDLoc(N2),
N2.getValueType());
else
Temp = DAG.getNode(ISD::ZERO_EXTEND, SDLoc(N2),
N2.getValueType(), SCC);
} else {
SCC = DAG.getSetCC(SDLoc(N0), MVT::i1, N0, N1, CC);
Temp = DAG.getNode(ISD::ZERO_EXTEND, SDLoc(N2),
N2.getValueType(), SCC);
}
AddToWorklist(SCC.getNode());
AddToWorklist(Temp.getNode());
if (N2C->isOne())
return Temp;
// shl setcc result by log2 n2c
return DAG.getNode(
ISD::SHL, DL, N2.getValueType(), Temp,
DAG.getConstant(N2C->getAPIntValue().logBase2(), SDLoc(Temp),
getShiftAmountTy(Temp.getValueType())));
SDValue Temp, SCC;
// zext (setcc n0, n1)
if (LegalTypes) {
SCC = DAG.getSetCC(DL, getSetCCResultType(N0.getValueType()), N0, N1, CC);
if (N2.getValueType().bitsLT(SCC.getValueType()))
Temp = DAG.getZeroExtendInReg(SCC, SDLoc(N2), N2.getValueType());
else
Temp = DAG.getNode(ISD::ZERO_EXTEND, SDLoc(N2), N2.getValueType(), SCC);
} else {
SCC = DAG.getSetCC(SDLoc(N0), MVT::i1, N0, N1, CC);
Temp = DAG.getNode(ISD::ZERO_EXTEND, SDLoc(N2), N2.getValueType(), SCC);
}
AddToWorklist(SCC.getNode());
AddToWorklist(Temp.getNode());
if (N2C->isOne())
return Temp;
// shl setcc result by log2 n2c
return DAG.getNode(ISD::SHL, DL, N2.getValueType(), Temp,
DAG.getConstant(N2C->getAPIntValue().logBase2(),
SDLoc(Temp),
getShiftAmountTy(Temp.getValueType())));
}
// Check to see if this is an integer abs.

54
llvm/test/CodeGen/AArch64/select_cc.ll Normal file
View File

@ -0,0 +1,54 @@
; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
; RUN: llc < %s -mtriple=aarch64 | FileCheck %s
define i64 @select_ogt_float(float %a, float %b) {
; CHECK-LABEL: select_ogt_float:
; CHECK: // %bb.0: // %entry
; CHECK-NEXT: fcmp s0, s1
; CHECK-NEXT: cset w8, gt
; CHECK-NEXT: lsl x0, x8, #2
; CHECK-NEXT: ret
entry:
%cc = fcmp ogt float %a, %b
%sel = select i1 %cc, i64 4, i64 0
ret i64 %sel
}
define i64 @select_ule_float_inverse(float %a, float %b) {
; CHECK-LABEL: select_ule_float_inverse:
; CHECK: // %bb.0: // %entry
; CHECK-NEXT: fcmp s0, s1
; CHECK-NEXT: cset w8, gt
; CHECK-NEXT: lsl x0, x8, #2
; CHECK-NEXT: ret
entry:
%cc = fcmp ule float %a, %b
%sel = select i1 %cc, i64 0, i64 4
ret i64 %sel
}
define i64 @select_eq_i32(i32 %a, i32 %b) {
; CHECK-LABEL: select_eq_i32:
; CHECK: // %bb.0: // %entry
; CHECK-NEXT: cmp w0, w1
; CHECK-NEXT: cset w8, eq
; CHECK-NEXT: lsl x0, x8, #2
; CHECK-NEXT: ret
entry:
%cc = icmp eq i32 %a, %b
%sel = select i1 %cc, i64 4, i64 0
ret i64 %sel
}
define i64 @select_ne_i32_inverse(i32 %a, i32 %b) {
; CHECK-LABEL: select_ne_i32_inverse:
; CHECK: // %bb.0: // %entry
; CHECK-NEXT: cmp w0, w1
; CHECK-NEXT: cset w8, eq
; CHECK-NEXT: lsl x0, x8, #2
; CHECK-NEXT: ret
entry:
%cc = icmp ne i32 %a, %b
%sel = select i1 %cc, i64 0, i64 4
ret i64 %sel
}

16
llvm/test/CodeGen/Thumb/branchless-cmp.ll
View File

@ -74,23 +74,17 @@ entry:
; CHECK-NEXT: lsls r0, r1, #2
}
; FIXME: This one hasn't changed actually
; but could look like test3b
define i32 @test4a(i32 %a, i32 %b) {
entry:
%cmp = icmp ne i32 %a, %b
%cond = select i1 %cmp, i32 0, i32 4
ret i32 %cond
; CHECK-LABEL: test4a:
; CHECK: bb.0:
; CHECK-NEXT: cmp r0, r1
; CHECK-NEXT: bne .LBB6_2
; CHECK-NEXT: bb.1:
; CHECK-NEXT: movs r0, #4
; CHECK-NEXT: bx lr
; CHECK-NEXT: .LBB6_2:
; CHECK-NEXT: movs r0, #0
; CHECK-NEXT: bx lr
; CHECK-NOT: b{{(ne)|(eq)}}
; CHECK: subs r0, r0, r1
; CHECK-NEXT: rsbs r1, r0, #0
; CHECK-NEXT: adcs r1, r0
; CHECK-NEXT: lsls r0, r1, #2
}
define i32 @test4b(i32 %a, i32 %b) {