[X86] Disable the NOP padding for branches when bundle is enabled

[skan]

Summary

When bundle is enabled, data fragment itself has a space to emit NOP to bundle-align instructions. The behaviour makes it impossible for us to determine whether the macro fusion really happen when emitting instructions. In addition, boundary-align fragment is also used to emit NOPs to align instructions, currently using them together sometimes makes code crazy.

[reames]

LGTM

[jyknight]

(Still worth considering removing the bundle_align feature entirely, but in the meantime, definitely good to not blow up).

[MaskRay]

(+1 considering removal of .bundle_align_mode)

llvm/lib/Target/X86/MCTargetDesc/X86AsmBackend.cpp

bool X86AsmBackend::allowAutoPadding() const {
   return (AlignBoundary != Align(1) && AlignBranchType != X86::AlignBranchNone);
 }
 
 bool X86AsmBackend::needAlign(MCObjectStreamer &OS) const {
   if (!OS.getAllowAutoPadding())
     return false;
   assert(allowAutoPadding() && "incorrect initialization!");
 
-  MCAssembler &Assembler = OS.getAssembler();
-  MCSection *Sec = OS.getCurrentSectionOnly();
   // To be Done: Currently don't deal with Bundle cases.
-  if (Assembler.isBundlingEnabled() && Sec->isBundleLocked())
+  if (OS.getAssembler().isBundlingEnabled())
     return false;
 
   // Branches only need to be aligned in 32-bit or 64-bit mode.
   if (!(STI.hasFeature(X86::Mode64Bit) || STI.hasFeature(X86::Mode32Bit)))
     return false;
 
   return true;
 }

llvm/test/MC/X86/align-branch-64-7a.s

+# Check using option --x86-align-branch-boundary=16 --x86-align-branch=fused+jcc --mc-relax-all with bundle won't make code crazy
+# RUN: llvm-mc -filetype=obj -triple x86_64-unknown-unknown --x86-align-branch-boundary=16 --x86-align-branch=fused+jcc --mc-relax-all %s | llvm-objdump -d  - > %t1
+# RUN: FileCheck --input-file=%t1 %s
+
+# CHECK: 0000000000000000 foo:
+# CHECK-NEXT:       0: 55                               pushq    %rbp
+# CHECK-NEXT:       1: 48 f7 c2 02 00 00 00             testq    $2, %rdx
+# CHECK-NEXT:       8: 0f 85 f2 ff ff ff                jne      {{.*}}
+# CHECK-NEXT:       e: 90                               nop
+# CHECK-NEXT:       f: 90                               nop
+# CHECK-NEXT:      10: 0f 8e ea ff ff ff                jle      {{.*}}
+
+    .text
+    .p2align 4
+foo:
+  push %rbp
+  # Will be bundle-aligning to 8 byte boundaries
+  .bundle_align_mode 3
+  test $2, %rdx
+  jne   foo
+# This jle is 6 bytes long and should have started at 0xe, so two bytes
+# of nop padding are inserted instead and it starts at 0x10
+  jle   foo