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[PowerPC] Materialize i64 constants using bit inversion
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
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@ -544,7 +544,7 @@ SDNode *PPCDAGToDAGISel::SelectBitfieldInsert(SDNode *N) {
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// Predict the number of instructions that would be generated by calling
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// SelectInt64(N).
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static unsigned SelectInt64Count(int64_t Imm) {
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static unsigned SelectInt64CountDirect(int64_t Imm) {
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// Assume no remaining bits.
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unsigned Remainder = 0;
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// Assume no shift required.
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@ -602,9 +602,21 @@ static unsigned SelectInt64Count(int64_t Imm) {
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return Result;
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}
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static unsigned SelectInt64Count(int64_t Imm) {
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unsigned DirectCount = SelectInt64CountDirect(Imm);
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// If might be cheaper to materialize the bit-inverted constant, and then
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// flip the bits (which takes one nor instruction).
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unsigned NotDirectCount = SelectInt64CountDirect(~(uint64_t) Imm) + 1;
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if (NotDirectCount < DirectCount)
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return NotDirectCount;
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return DirectCount;
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}
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// Select a 64-bit constant. For cost-modeling purposes, SelectInt64Count
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// (above) needs to be kept in sync with this function.
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static SDNode *SelectInt64(SelectionDAG *CurDAG, SDLoc dl, int64_t Imm) {
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static SDNode *SelectInt64Direct(SelectionDAG *CurDAG, SDLoc dl, int64_t Imm) {
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// Assume no remaining bits.
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unsigned Remainder = 0;
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// Assume no shift required.
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@ -678,6 +690,22 @@ static SDNode *SelectInt64(SelectionDAG *CurDAG, SDLoc dl, int64_t Imm) {
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return Result;
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}
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static SDNode *SelectInt64(SelectionDAG *CurDAG, SDLoc dl, int64_t Imm) {
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unsigned DirectCount = SelectInt64CountDirect(Imm);
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// If might be cheaper to materialize the bit-inverted constant, and then
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// flip the bits (which takes one nor instruction).
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unsigned NotDirectCount = SelectInt64CountDirect(~(uint64_t) Imm) + 1;
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if (NotDirectCount < DirectCount) {
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SDValue NotDirectVal =
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SDValue(SelectInt64Direct(CurDAG, dl, ~(uint64_t) Imm), 0);
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return CurDAG->getMachineNode(PPC::NOR8, dl, MVT::i64, NotDirectVal,
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NotDirectVal);
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}
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return SelectInt64Direct(CurDAG, dl, Imm);
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}
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// Select a 64-bit constant.
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static SDNode *SelectInt64(SelectionDAG *CurDAG, SDNode *N) {
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SDLoc dl(N);
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20
test/CodeGen/PowerPC/constants-i64.ll
Normal file
20
test/CodeGen/PowerPC/constants-i64.ll
Normal file
@ -0,0 +1,20 @@
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; RUN: llc -mcpu=ppc64 < %s | FileCheck %s
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target datalayout = "E-m:e-i64:64-n32:64"
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target triple = "powerpc64-unknown-linux-gnu"
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; Function Attrs: nounwind readnone
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define i64 @cn1() #0 {
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entry:
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ret i64 281474976710655
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; CHECK-LABEL: @cn1
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; CHECK: li [[REG1:[0-9]+]], 0
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; CHECK: ori [[REG2:[0-9]+]], [[REG1]], 65535
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; CHECK: sldi [[REG3:[0-9]+]], [[REG2]], 48
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; CHECK: nor 3, [[REG3]], [[REG3]]
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; CHECK: blr
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}
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attributes #0 = { nounwind readnone }
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