Use multiple 0x66 prefixes so that all nops up to 15 bytes are a single instruction.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@120147 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Target/X86/X86AsmBackend.cpp b/lib/Target/X86/X86AsmBackend.cpp
index fd823bf52448d3ec1843cafeb0a22bfd63ad6325..ab8f62874527254d65e374f73047c6d13f705744 100644 (file)
--- a/lib/Target/X86/X86AsmBackend.cpp
+++ b/lib/Target/X86/X86AsmBackend.cpp
@@ -211,10 +211,8 @@ void X86AsmBackend::RelaxInstruction(const MCInst &Inst, MCInst &Res) const {
 /// 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] = {
+  static const uint8_t Nops[10][10] = {
     // nop
     {0x90},
     // xchg %ax,%ax
@@ -235,30 +233,16 @@ bool X86AsmBackend::WriteNopData(uint64_t Count, MCObjectWriter *OW) const {
     {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},
-    // nopw %cs:0L(%[re]ax,%[re]ax,1)
-    {0x66, 0x66, 0x2e, 0x0f, 0x1f, 0x84, 0x00, 0x00, 0x00, 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]);
+  const uint64_t OptimalCount = (Count < 16) ? Count : 15;
+  const uint64_t Prefixes = OptimalCount <= 10 ? 0 : OptimalCount - 10;
+  for (uint64_t i = 0, e = Prefixes; i != e; i++)
+    OW->Write8(0x66);
+  const uint64_t Rest = OptimalCount - Prefixes;
+  for (uint64_t i = 0, e = Rest; i != e; i++)
+    OW->Write8(Nops[Rest - 1][i]);
 
   // Finish with single byte nops.
   for (uint64_t i = OptimalCount, e = Count; i != e; ++i)

diff --git a/test/MC/MachO/x86_32-optimal_nop.s b/test/MC/MachO/x86_32-optimal_nop.s
index 09c541f56035f0342687249fe4b340c93e71d31b..31cf24028345a3d83bab2089c901d6eccf27bdbc 100644 (file)
--- a/test/MC/MachO/x86_32-optimal_nop.s
+++ b/test/MC/MachO/x86_32-optimal_nop.s
@@ -192,7 +192,7 @@ f0:
 // CHECK:    ),
 // CHECK:   ('_relocations', [
 // CHECK:   ])
-// CHECK:   ('_section_data', 'c390c300 00000000 00000000 00000000 c3c36690 c3000000 00000000 00000000 c30f1f00 c3000000 00000000 00000000 c3c3c3c3 0f1f4000 c3000000 00000000 c3c3c30f 1f440000 c3000000 00000000 c3c3660f 1f440000 c3000000 00000000 c30f1f80 00000000 c3000000 00000000 c3c3c3c3 c3c3c3c3 c3000000 00000000 c3c3c3c3 c3c3c366 0f1f8400 00000000 c3000000 00000000 00000000 00000000 c3c3c3c3 c3c3c366 0f1f8400 00000000 c3000000 00000000 00000000 00000000 c3c3c3c3 c366662e 0f1f8400 00000000 c3000000 00000000 00000000 00000000 c3c3c3c3 660f1f44 0000660f 1f440000 c3000000 00000000 00000000 00000000 c3c3c366 0f1f4400 000f1f80 00000000 c3000000 00000000 00000000 00000000 c3c30f1f 80000000 000f1f80 00000000 c3000000 00000000 00000000 00000000 c30f1f80 00000000 0f1f8400 00000000 c3')
+// CHECK:   ('_section_data', 'c390c300 00000000 00000000 00000000 c3c36690 c3000000 00000000 00000000 c30f1f00 c3000000 00000000 00000000 c3c3c3c3 0f1f4000 c3000000 00000000 c3c3c30f 1f440000 c3000000 00000000 c3c3660f 1f440000 c3000000 00000000 c30f1f80 00000000 c3000000 00000000 c3c3c3c3 c3c3c3c3 c3000000 00000000 c3c3c3c3 c3c3c366 0f1f8400 00000000 c3000000 00000000 00000000 00000000 c3c3c3c3 c3c3c366 0f1f8400 00000000 c3000000 00000000 00000000 00000000 c3c3c3c3 c366662e 0f1f8400 00000000 c3000000 00000000 00000000 00000000 c3c3c3c3 6666662e 0f1f8400 00000000 c3000000 00000000 00000000 00000000 c3c3c366 6666662e 0f1f8400 00000000 c3000000 00000000 00000000 00000000 c3c36666 6666662e 0f1f8400 00000000 c3000000 00000000 00000000 00000000 c3666666 6666662e 0f1f8400 00000000 c3')
 // CHECK:     # Section 1
 // CHECK:    (('section_name', '__const\x00\x00\x00\x00\x00\x00\x00\x00\x00')
 // CHECK:     ('segment_name', '__TEXT\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00')