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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 | 04ab19cb1486725de7f201dddf596137b112c17e (patch) | |
| tree | 455a775ab9f00e09870b2b18ae5b633fee0b0b50 | |
| parent | 15b0d97068560cd7564cf4f975c2cbc1f5398102 (diff) | |
Add comment about potential partial register stall.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@91220 91177308-0d34-0410-b5e6-96231b3b80d8
| -rw-r--r-- | lib/Target/X86/X86InstrInfo.cpp | 5 |
1 files changed, 5 insertions, 0 deletions
diff --git a/lib/Target/X86/X86InstrInfo.cpp b/lib/Target/X86/X86InstrInfo.cpp index d45dccedb6..87f6fc039b 100644 --- a/lib/Target/X86/X86InstrInfo.cpp +++ b/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) |