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| author | Evan Cheng <evan.cheng@apple.com> | 2009-12-12 18:55:26 +0000 |
|---|---|---|
| committer | Evan Cheng <evan.cheng@apple.com> | 2009-12-12 18:55:26 +0000 |
| commit | 3974c8de516d89b0ae5cd1ce48a54c829685a34c (patch) | |
| tree | 92d5536bd3abf80327bf05319380bd38e1d1f8ed /llvm/lib/Target | |
| parent | 6d6eaafa8cc5d97c4c5525aa62179f330aac2f1a (diff) | |
| download | bcm5719-llvm-3974c8de516d89b0ae5cd1ce48a54c829685a34c.tar.gz bcm5719-llvm-3974c8de516d89b0ae5cd1ce48a54c829685a34c.zip | |
Add comment about potential partial register stall.
llvm-svn: 91220
Diffstat (limited to 'llvm/lib/Target')
| -rw-r--r-- | llvm/lib/Target/X86/X86InstrInfo.cpp | 5 |
1 files changed, 5 insertions, 0 deletions
diff --git a/llvm/lib/Target/X86/X86InstrInfo.cpp b/llvm/lib/Target/X86/X86InstrInfo.cpp index d45dccedb6a..87f6fc039bb 100644 --- a/llvm/lib/Target/X86/X86InstrInfo.cpp +++ b/llvm/lib/Target/X86/X86InstrInfo.cpp @@ -1081,6 +1081,11 @@ X86InstrInfo::convertToThreeAddressWithLEA(unsigned MIOpc, // Build and insert into an implicit UNDEF value. This is OK because // well be shifting and then extracting the lower 16-bits. + // This has the potential to cause partial stall. e.g. + // movw (%rbp,%rcx,2), %dx + // leal -65(%rdx), %esi + // But testing has shown this *does* help performance (at least on modern + // x86 machines). BuildMI(*MFI, MBBI, MI->getDebugLoc(), get(X86::IMPLICIT_DEF), leaInReg); MachineInstr *InsMI = BuildMI(*MFI, MBBI, MI->getDebugLoc(), get(X86::INSERT_SUBREG),leaInReg) |
