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[PPC64] Use mfocrf in prologue when we only need to save 1 nonvolatile CR field 

In the ELFv2 ABI, we are not required to save all CR fields. If only one
nonvolatile CR field is clobbered, use mfocrf instead of mfcr to
selectively save the field, because mfocrf has short latency compares to
mfcr.

Thanks Nemanja's invaluable hint!
Reviewers: nemanjai tjablin hfinkel kbarton

http://reviews.llvm.org/D17749

llvm-svn: 266038
This commit is contained in:
Chuang-Yu Cheng 2016-04-12 03:04:44 +00:00
parent 9b3f99e50f
commit 6efde2fb45
3 changed files with 37 additions and 9 deletions
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24
llvm/lib/Target/PowerPC/PPCFrameLowering.cpp
View File

@ -838,11 +838,15 @@ void PPCFrameLowering::emitPrologue(MachineFunction &MF,
// If we need to spill the CR and the LR but we don't have two separate
// registers available, we must spill them one at a time
if (MustSaveCR && SingleScratchReg && MustSaveLR) {
// FIXME: In the ELFv2 ABI, we are not required to save all CR fields.
// If only one or two CR fields are clobbered, it could be more
// efficient to use mfocrf to selectively save just those fields.
// In the ELFv2 ABI, we are not required to save all CR fields.
// If only one or two CR fields are clobbered, it is more efficient to use
// mfocrf to selectively save just those fields, because mfocrf has short
// latency compares to mfcr.
unsigned MfcrOpcode = PPC::MFCR8;
if (isELFv2ABI && MustSaveCRs.size() == 1)
MfcrOpcode = PPC::MFOCRF8;
MachineInstrBuilder MIB =
BuildMI(MBB, MBBI, dl, TII.get(PPC::MFCR8), TempReg);
BuildMI(MBB, MBBI, dl, TII.get(MfcrOpcode), TempReg);
for (unsigned i = 0, e = MustSaveCRs.size(); i != e; ++i)
MIB.addReg(MustSaveCRs[i], RegState::ImplicitKill);
BuildMI(MBB, MBBI, dl, TII.get(PPC::STW8))
@ -856,11 +860,15 @@ void PPCFrameLowering::emitPrologue(MachineFunction &MF,
if (MustSaveCR &&
!(SingleScratchReg && MustSaveLR)) { // will only occur for PPC64
// FIXME: In the ELFv2 ABI, we are not required to save all CR fields.
// If only one or two CR fields are clobbered, it could be more
// efficient to use mfocrf to selectively save just those fields.
// In the ELFv2 ABI, we are not required to save all CR fields.
// If only one or two CR fields are clobbered, it is more efficient to use
// mfocrf to selectively save just those fields, because mfocrf has short
// latency compares to mfcr.
unsigned MfcrOpcode = PPC::MFCR8;
if (isELFv2ABI && MustSaveCRs.size() == 1)
MfcrOpcode = PPC::MFOCRF8;
MachineInstrBuilder MIB =
BuildMI(MBB, MBBI, dl, TII.get(PPC::MFCR8), TempReg);
BuildMI(MBB, MBBI, dl, TII.get(MfcrOpcode), TempReg);
for (unsigned i = 0, e = MustSaveCRs.size(); i != e; ++i)
MIB.addReg(MustSaveCRs[i], RegState::ImplicitKill);
}

20
llvm/test/CodeGen/PowerPC/crsave.ll
View File

@ -1,5 +1,6 @@
; RUN: llc -O0 -disable-fp-elim -mtriple=powerpc-unknown-linux-gnu -mcpu=g5 < %s | FileCheck %s -check-prefix=PPC32
; RUN: llc -O0 -mtriple=powerpc64-unknown-linux-gnu -mcpu=g5 < %s | FileCheck %s -check-prefix=PPC64
; RUN: llc -O0 -mtriple=powerpc64le-unknown-linux-gnu < %s | FileCheck %s -check-prefix=PPC64-ELFv2
declare void @foo()
@ -60,3 +61,22 @@ entry:
; PPC64: mtocrf 16, 12
; PPC64: mtocrf 8, 12
; Generate mfocrf in prologue when we need to save 1 nonvolatile CR field
define void @cloberOneNvCrField() {
entry:
tail call void asm sideeffect "# clobbers", "~{cr2}"()
ret void
; PPC64-ELFv2-LABEL: @cloberOneNvCrField
; PPC64-ELFv2: mfocrf [[REG1:[0-9]+]], 32
}
; Generate mfcr in prologue when we need to save all nonvolatile CR field
define void @cloberAllNvCrField() {
entry:
tail call void asm sideeffect "# clobbers", "~{cr2},~{cr3},~{cr4}"()
ret void
; PPC64-ELFv2-LABEL: @cloberAllNvCrField
; PPC64-ELFv2: mfcr [[REG1:[0-9]+]]
}

2
llvm/test/CodeGen/PowerPC/pr26690.ll
View File

@ -101,7 +101,7 @@ if.end16: ; preds = %entry, %if.end13, %
ret i32 2
}
; CHECK: mfcr {{[0-9]+}}
; CHECK: mfocrf {{[0-9]+}}
!llvm.ident = !{!0}