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[PowerPC] Materialize i64 constants using bit inversion

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Materializing full 64-bit constants on PPC64 can be expensive, requiring up to
5 instructions depending on the locations of the non-zero bits. Sometimes
materializing the bit-reversed constant, and then flipping the bits, requires
fewer instructions than the direct method. If so, do that instead.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@225132 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Hal Finkel 2015-01-04 12:35:03 +00:00
parent 5a9cd4d44e
commit d138a7bb3f
2 changed files with 50 additions and 2 deletions
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32
lib/Target/PowerPC/PPCISelDAGToDAG.cpp
View File

@ -544,7 +544,7 @@ SDNode *PPCDAGToDAGISel::SelectBitfieldInsert(SDNode *N) {
// Predict the number of instructions that would be generated by calling
// SelectInt64(N).
static unsigned SelectInt64Count(int64_t Imm) {
static unsigned SelectInt64CountDirect(int64_t Imm) {
// Assume no remaining bits.
unsigned Remainder = 0;
// Assume no shift required.
@ -602,9 +602,21 @@ static unsigned SelectInt64Count(int64_t Imm) {
return Result;
}
static unsigned SelectInt64Count(int64_t Imm) {
unsigned DirectCount = SelectInt64CountDirect(Imm);
// If might be cheaper to materialize the bit-inverted constant, and then
// flip the bits (which takes one nor instruction).
unsigned NotDirectCount = SelectInt64CountDirect(~(uint64_t) Imm) + 1;
if (NotDirectCount < DirectCount)
return NotDirectCount;
return DirectCount;
}
// Select a 64-bit constant. For cost-modeling purposes, SelectInt64Count
// (above) needs to be kept in sync with this function.
static SDNode *SelectInt64(SelectionDAG *CurDAG, SDLoc dl, int64_t Imm) {
static SDNode *SelectInt64Direct(SelectionDAG *CurDAG, SDLoc dl, int64_t Imm) {
// Assume no remaining bits.
unsigned Remainder = 0;
// Assume no shift required.
@ -678,6 +690,22 @@ static SDNode *SelectInt64(SelectionDAG *CurDAG, SDLoc dl, int64_t Imm) {
return Result;
}
static SDNode *SelectInt64(SelectionDAG *CurDAG, SDLoc dl, int64_t Imm) {
unsigned DirectCount = SelectInt64CountDirect(Imm);
// If might be cheaper to materialize the bit-inverted constant, and then
// flip the bits (which takes one nor instruction).
unsigned NotDirectCount = SelectInt64CountDirect(~(uint64_t) Imm) + 1;
if (NotDirectCount < DirectCount) {
SDValue NotDirectVal =
SDValue(SelectInt64Direct(CurDAG, dl, ~(uint64_t) Imm), 0);
return CurDAG->getMachineNode(PPC::NOR8, dl, MVT::i64, NotDirectVal,
NotDirectVal);
}
return SelectInt64Direct(CurDAG, dl, Imm);
}
// Select a 64-bit constant.
static SDNode *SelectInt64(SelectionDAG *CurDAG, SDNode *N) {
SDLoc dl(N);

20
test/CodeGen/PowerPC/constants-i64.ll Normal file
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@ -0,0 +1,20 @@
; RUN: llc -mcpu=ppc64 < %s | FileCheck %s
target datalayout = "E-m:e-i64:64-n32:64"
target triple = "powerpc64-unknown-linux-gnu"
; Function Attrs: nounwind readnone
define i64 @cn1() #0 {
entry:
ret i64 281474976710655
; CHECK-LABEL: @cn1
; CHECK: li [[REG1:[0-9]+]], 0
; CHECK: ori [[REG2:[0-9]+]], [[REG1]], 65535
; CHECK: sldi [[REG3:[0-9]+]], [[REG2]], 48
; CHECK: nor 3, [[REG3]], [[REG3]]
; CHECK: blr
}
attributes #0 = { nounwind readnone }