MC: Add TargetAsmBackend::WriteNopData and use to eliminate some target dependencies in MCMachOStreamer and MCAssembler.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@99248 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Target/X86/X86AsmBackend.cpp b/lib/Target/X86/X86AsmBackend.cpp
index e918cb0..3e4e2b5 100644
--- a/lib/Target/X86/X86AsmBackend.cpp
+++ b/lib/Target/X86/X86AsmBackend.cpp
@@ -53,6 +53,8 @@
}
void RelaxInstruction(const MCInstFragment *IF, MCInst &Res) const;
+
+ bool WriteNopData(uint64_t Count, MCObjectWriter *OW) const;
};
static unsigned getRelaxedOpcode(unsigned Op) {
@@ -98,6 +100,67 @@
Res.setOpcode(RelaxedOp);
}
+/// WriteNopData - Write optimal nops to the output file for the \arg Count
+/// bytes. This returns the number of bytes written. It may return 0 if
+/// the \arg Count is more than the maximum optimal nops.
+///
+/// FIXME this is X86 32-bit specific and should move to a better place.
+bool X86AsmBackend::WriteNopData(uint64_t Count, MCObjectWriter *OW) const {
+ static const uint8_t Nops[16][16] = {
+ // nop
+ {0x90},
+ // xchg %ax,%ax
+ {0x66, 0x90},
+ // nopl (%[re]ax)
+ {0x0f, 0x1f, 0x00},
+ // nopl 0(%[re]ax)
+ {0x0f, 0x1f, 0x40, 0x00},
+ // nopl 0(%[re]ax,%[re]ax,1)
+ {0x0f, 0x1f, 0x44, 0x00, 0x00},
+ // nopw 0(%[re]ax,%[re]ax,1)
+ {0x66, 0x0f, 0x1f, 0x44, 0x00, 0x00},
+ // nopl 0L(%[re]ax)
+ {0x0f, 0x1f, 0x80, 0x00, 0x00, 0x00, 0x00},
+ // nopl 0L(%[re]ax,%[re]ax,1)
+ {0x0f, 0x1f, 0x84, 0x00, 0x00, 0x00, 0x00, 0x00},
+ // nopw 0L(%[re]ax,%[re]ax,1)
+ {0x66, 0x0f, 0x1f, 0x84, 0x00, 0x00, 0x00, 0x00, 0x00},
+ // nopw %cs:0L(%[re]ax,%[re]ax,1)
+ {0x66, 0x2e, 0x0f, 0x1f, 0x84, 0x00, 0x00, 0x00, 0x00, 0x00},
+ // nopl 0(%[re]ax,%[re]ax,1)
+ // nopw 0(%[re]ax,%[re]ax,1)
+ {0x0f, 0x1f, 0x44, 0x00, 0x00,
+ 0x66, 0x0f, 0x1f, 0x44, 0x00, 0x00},
+ // nopw 0(%[re]ax,%[re]ax,1)
+ // nopw 0(%[re]ax,%[re]ax,1)
+ {0x66, 0x0f, 0x1f, 0x44, 0x00, 0x00,
+ 0x66, 0x0f, 0x1f, 0x44, 0x00, 0x00},
+ // nopw 0(%[re]ax,%[re]ax,1)
+ // nopl 0L(%[re]ax) */
+ {0x66, 0x0f, 0x1f, 0x44, 0x00, 0x00,
+ 0x0f, 0x1f, 0x80, 0x00, 0x00, 0x00, 0x00},
+ // nopl 0L(%[re]ax)
+ // nopl 0L(%[re]ax)
+ {0x0f, 0x1f, 0x80, 0x00, 0x00, 0x00, 0x00,
+ 0x0f, 0x1f, 0x80, 0x00, 0x00, 0x00, 0x00},
+ // nopl 0L(%[re]ax)
+ // nopl 0L(%[re]ax,%[re]ax,1)
+ {0x0f, 0x1f, 0x80, 0x00, 0x00, 0x00, 0x00,
+ 0x0f, 0x1f, 0x84, 0x00, 0x00, 0x00, 0x00, 0x00}
+ };
+
+ // Write an optimal sequence for the first 15 bytes.
+ uint64_t OptimalCount = (Count < 16) ? Count : 15;
+ for (uint64_t i = 0, e = OptimalCount; i != e; i++)
+ OW->Write8(Nops[OptimalCount - 1][i]);
+
+ // Finish with single byte nops.
+ for (uint64_t i = OptimalCount, e = Count; i != e; ++i)
+ OW->Write8(0x90);
+
+ return true;
+}
+
/* *** */
class ELFX86AsmBackend : public X86AsmBackend {