llvm-mc: Improve handling of implicit alignment for magic section directives

(e.g., .objc_message_refs).
 - Just emit a .align when we see the directive; this isn't exactly what 'as'
   does but in practice it should be ok, at least for now. See FIXME.

llvm-svn: 79697

2 files changed, 21 insertions, 19 deletions

diff --git a/llvm/test/MC/MachO/sections.s b/llvm/test/MC/MachO/sections.s
index 7b7f9a1e43f..97716025801 100644
--- a/llvm/test/MC/MachO/sections.s
+++ b/llvm/test/MC/MachO/sections.s
@@ -121,8 +121,7 @@
 // CHECK:     ('address', 0)
 // CHECK:     ('size', 0)
 // CHECK:     ('offset', 2464)
-        // FIXME: We aren't setting alignment correctly yet.
-// CHECX:     ('alignment', 2)
+// CHECK:     ('alignment', 2)
 // CHECK:     ('reloc_offset', 0)
 // CHECK:     ('num_reloc', 0)
 // CHECK:     ('flags', 0x3)
@@ -135,8 +134,7 @@
 // CHECK:     ('address', 0)
 // CHECK:     ('size', 0)
 // CHECK:     ('offset', 2464)
-        // FIXME: We aren't setting alignment correctly yet.
-// CHECX:     ('alignment', 3)
+// CHECK:     ('alignment', 3)
 // CHECK:     ('reloc_offset', 0)
 // CHECK:     ('num_reloc', 0)
 // CHECK:     ('flags', 0x4)
@@ -149,8 +147,7 @@
 // CHECK:     ('address', 0)
 // CHECK:     ('size', 0)
 // CHECK:     ('offset', 2464)
-        // FIXME: We aren't setting alignment correctly yet.
-// CHECX:     ('alignment', 4)
+// CHECK:     ('alignment', 4)
 // CHECK:     ('reloc_offset', 0)
 // CHECK:     ('num_reloc', 0)
 // CHECK:     ('flags', 0xe)
@@ -241,8 +238,7 @@
 // CHECK:     ('address', 0)
 // CHECK:     ('size', 0)
 // CHECK:     ('offset', 2464)
-        // FIXME: We aren't setting alignment correctly yet.
-// CHECX:     ('alignment', 2)
+// CHECK:     ('alignment', 2)
 // CHECK:     ('reloc_offset', 0)
 // CHECK:     ('num_reloc', 0)
 // CHECK:     ('flags', 0x6)
@@ -255,8 +251,7 @@
 // CHECK:     ('address', 0)
 // CHECK:     ('size', 0)
 // CHECK:     ('offset', 2464)
-        // FIXME: We aren't setting alignment correctly yet.
-// CHECX:     ('alignment', 2)
+// CHECK:     ('alignment', 2)
 // CHECK:     ('reloc_offset', 0)
 // CHECK:     ('num_reloc', 0)
 // CHECK:     ('flags', 0x7)
@@ -282,8 +277,7 @@
 // CHECK:     ('address', 0)
 // CHECK:     ('size', 0)
 // CHECK:     ('offset', 2464)
-        // FIXME: We aren't setting alignment correctly yet.
-// CHECX:     ('alignment', 2)
+// CHECK:     ('alignment', 2)
 // CHECK:     ('reloc_offset', 0)
 // CHECK:     ('num_reloc', 0)
 // CHECK:     ('flags', 0x9)
@@ -296,8 +290,7 @@
 // CHECK:     ('address', 0)
 // CHECK:     ('size', 0)
 // CHECK:     ('offset', 2464)
-        // FIXME: We aren't setting alignment correctly yet.
-// CHECX:     ('alignment', 2)
+// CHECK:     ('alignment', 2)
 // CHECK:     ('reloc_offset', 0)
 // CHECK:     ('num_reloc', 0)
 // CHECK:     ('flags', 0xa)
@@ -427,8 +420,7 @@
 // CHECK:     ('address', 0)
 // CHECK:     ('size', 0)
 // CHECK:     ('offset', 2464)
-        // FIXME: We aren't setting alignment correctly yet.
-// CHECX:     ('alignment', 2)
+// CHECK:     ('alignment', 2)
 // CHECK:     ('reloc_offset', 0)
 // CHECK:     ('num_reloc', 0)
 // CHECK:     ('flags', 0x10000005)
@@ -441,8 +433,7 @@
 // CHECK:     ('address', 0)
 // CHECK:     ('size', 0)
 // CHECK:     ('offset', 2464)
-        // FIXME: We aren't setting alignment correctly yet.
-// CHECX:     ('alignment', 2)
+// CHECK:     ('alignment', 2)
 // CHECK:     ('reloc_offset', 0)
 // CHECK:     ('num_reloc', 0)
 // CHECK:     ('flags', 0x10000005)
diff --git a/llvm/tools/llvm-mc/AsmParser.cpp b/llvm/tools/llvm-mc/AsmParser.cpp
index 9db0ac0351b..19781212976 100644
--- a/llvm/tools/llvm-mc/AsmParser.cpp
+++ b/llvm/tools/llvm-mc/AsmParser.cpp
@@ -794,13 +794,24 @@ bool AsmParser::ParseDirectiveSectionSwitch(const char *Segment,
   
   // FIXME: Arch specific.
   // FIXME: Cache this!
-  // FIXME: Handle the implicit alignment!!
   MCSection *S = 0; // Ctx.GetSection(Section);
   if (S == 0)
     S = MCSectionMachO::Create(Segment, Section, TAA, StubSize,
                                SectionKind(), Ctx);
   
   Out.SwitchSection(S);
+
+  // Set the implicit alignment, if any.
+  //
+  // FIXME: This isn't really what 'as' does; I think it just uses the implicit
+  // alignment on the section (e.g., if one manually inserts bytes into the
+  // section, then just issueing the section switch directive will not realign
+  // the section. However, this is arguably more reasonable behavior, and there
+  // is no good reason for someone to intentionally emit incorrectly sized
+  // values into the implicitly aligned sections.
+  if (Align)
+    Out.EmitValueToAlignment(Align, 0, 1, 0);
+
   return false;
 }