diff options
Diffstat (limited to 'llvm/lib')
| -rw-r--r-- | llvm/lib/Target/X86/MCTargetDesc/X86AsmBackend.cpp | 25 |
1 files changed, 23 insertions, 2 deletions
diff --git a/llvm/lib/Target/X86/MCTargetDesc/X86AsmBackend.cpp b/llvm/lib/Target/X86/MCTargetDesc/X86AsmBackend.cpp index da280547c4b..dffda521767 100644 --- a/llvm/lib/Target/X86/MCTargetDesc/X86AsmBackend.cpp +++ b/llvm/lib/Target/X86/MCTargetDesc/X86AsmBackend.cpp @@ -94,6 +94,14 @@ cl::opt<X86AlignBranchKind, true, cl::parser<std::string>> X86AlignBranch( "indirect indicates indirect jumps."), cl::location(X86AlignBranchKindLoc)); +cl::opt<bool> X86AlignBranchWithin32BBoundaries( + "x86-branches-within-32B-boundaries", cl::init(false), + cl::desc( + "Align selected instructions to mitigate negative performance impact " + "of Intel's micro code update for errata skx102. May break " + "assumptions about labels corresponding to particular instructions, " + "and should be used with caution.")); + class X86ELFObjectWriter : public MCELFObjectTargetWriter { public: X86ELFObjectWriter(bool is64Bit, uint8_t OSABI, uint16_t EMachine, @@ -119,8 +127,21 @@ public: X86AsmBackend(const Target &T, const MCSubtargetInfo &STI) : MCAsmBackend(support::little), STI(STI), MCII(T.createMCInstrInfo()) { - AlignBoundary = assumeAligned(X86AlignBranchBoundary); - AlignBranchType = X86AlignBranchKindLoc; + if (X86AlignBranchWithin32BBoundaries) { + // At the moment, this defaults to aligning fused branches, unconditional + // jumps, and (unfused) conditional jumps with nops. Both the + // instructions aligned and the alignment method (nop vs prefix) may + // change in the future. + AlignBoundary = assumeAligned(32);; + AlignBranchType.addKind(X86::AlignBranchFused); + AlignBranchType.addKind(X86::AlignBranchJcc); + AlignBranchType.addKind(X86::AlignBranchJmp); + } + // Allow overriding defaults set by master flag + if (X86AlignBranchBoundary.getNumOccurrences()) + AlignBoundary = assumeAligned(X86AlignBranchBoundary); + if (X86AlignBranch.getNumOccurrences()) + AlignBranchType = X86AlignBranchKindLoc; } bool allowAutoPadding() const override; |
