Reduce the size of MCRelaxableFragment.

MCRelaxableFragment previously kept a copy of MCSubtargetInfo and
MCInst to enable re-encoding the MCInst later during relaxation. A copy
of MCSubtargetInfo (instead of a reference or pointer) was needed
because the feature bits could be modified by the parser.

This commit replaces the MCSubtargetInfo copy in MCRelaxableFragment
with a constant reference to MCSubtargetInfo. The copies of
MCSubtargetInfo are kept in MCContext, and the target parsers are now
responsible for asking MCContext to provide a copy whenever the feature
bits of MCSubtargetInfo have to be toggled.
 
With this patch, I saw a 4% reduction in peak memory usage when I
compiled verify-uselistorder.lto.bc using llc.

rdar://problem/21736951

Differential Revision: http://reviews.llvm.org/D14346

llvm-svn: 253127

1 files changed, 6 insertions, 4 deletions

diff --git a/llvm/lib/Target/X86/AsmParser/X86AsmInstrumentation.h b/llvm/lib/Target/X86/AsmParser/X86AsmInstrumentation.h
index 19ebcc44f61..470ceadb0aa 100644
--- a/llvm/lib/Target/X86/AsmParser/X86AsmInstrumentation.h
+++ b/llvm/lib/Target/X86/AsmParser/X86AsmInstrumentation.h
@@ -28,7 +28,8 @@ class X86AsmInstrumentation;
 
 X86AsmInstrumentation *
 CreateX86AsmInstrumentation(const MCTargetOptions &MCOptions,
-                            const MCContext &Ctx, const MCSubtargetInfo &STI);
+                            const MCContext &Ctx,
+                            const MCSubtargetInfo *&STI);
 
 class X86AsmInstrumentation {
 public:
@@ -48,15 +49,16 @@ public:
 protected:
   friend X86AsmInstrumentation *
   CreateX86AsmInstrumentation(const MCTargetOptions &MCOptions,
-                              const MCContext &Ctx, const MCSubtargetInfo &STI);
+                              const MCContext &Ctx,
+                              const MCSubtargetInfo *&STI);
 
-  X86AsmInstrumentation(const MCSubtargetInfo &STI);
+  X86AsmInstrumentation(const MCSubtargetInfo *&STI);
 
   unsigned GetFrameRegGeneric(const MCContext &Ctx, MCStreamer &Out);
 
   void EmitInstruction(MCStreamer &Out, const MCInst &Inst);
 
-  const MCSubtargetInfo &STI;
+  const MCSubtargetInfo *&STI;
 
   unsigned InitialFrameReg;
 };