diff options
Diffstat (limited to 'llvm/lib/Target/X86/X86MCInstLower.cpp')
| -rw-r--r-- | llvm/lib/Target/X86/X86MCInstLower.cpp | 17 |
1 files changed, 17 insertions, 0 deletions
diff --git a/llvm/lib/Target/X86/X86MCInstLower.cpp b/llvm/lib/Target/X86/X86MCInstLower.cpp index e20d1ee2ae5..2fc9a2af01d 100644 --- a/llvm/lib/Target/X86/X86MCInstLower.cpp +++ b/llvm/lib/Target/X86/X86MCInstLower.cpp @@ -1031,6 +1031,20 @@ void X86AsmPrinter::LowerTlsAddr(X86MCInstLower &MCInstLowering, } } +/// Return the longest nop which can be efficiently decoded for the given +/// target cpu. 15-bytes is the longest single NOP instruction, but some +/// platforms can't decode the longest forms efficiently. +static unsigned MaxLongNopLength(const MCSubtargetInfo &STI) { + uint64_t MaxNopLength = 10; + if (STI.getFeatureBits()[X86::ProcIntelSLM]) + MaxNopLength = 7; + else if (STI.getFeatureBits()[X86::FeatureFast15ByteNOP]) + MaxNopLength = 15; + else if (STI.getFeatureBits()[X86::FeatureFast11ByteNOP]) + MaxNopLength = 11; + return MaxNopLength; +} + /// Emit the largest nop instruction smaller than or equal to \p NumBytes /// bytes. Return the size of nop emitted. static unsigned EmitNop(MCStreamer &OS, unsigned NumBytes, bool Is64Bit, @@ -1041,6 +1055,9 @@ static unsigned EmitNop(MCStreamer &OS, unsigned NumBytes, bool Is64Bit, return 1; } + // Cap a single nop emission at the profitable value for the target + NumBytes = std::min(NumBytes, MaxLongNopLength(STI)); + unsigned NopSize; unsigned Opc, BaseReg, ScaleVal, IndexReg, Displacement, SegmentReg; IndexReg = Displacement = SegmentReg = 0; |
