llvm-mc: Add a -mc-relax-all option, which relaxes every fixup. We always need

exactly two passes in that case, and don't ever need to recompute any layout,
so this is a nice baseline for relaxation performance.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@99563 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/MC/MCAssembler.h

@@ -624,6 +624,7 @@ private:
 
   std::vector<IndirectSymbolData> IndirectSymbols;
 
+  unsigned RelaxAll : 1;
   unsigned SubsectionsViaSymbols : 1;
 
 private:
@@ -727,6 +728,9 @@ public:
     SubsectionsViaSymbols = Value;
   }
 
+  bool getRelaxAll() const { return RelaxAll; }
+  void setRelaxAll(bool Value) { RelaxAll = Value; }
+
   /// @name Section List Access
   /// @{
 

include/llvm/MC/MCStreamer.h

@@ -308,7 +308,8 @@ class TargetAsmBackend;
   /// createMachOStream - Create a machine code streamer which will generative
   /// Mach-O format object files.
   MCStreamer *createMachOStreamer(MCContext &Ctx, TargetAsmBackend &TAB,
-                                  raw_ostream &OS, MCCodeEmitter *CE);
+                                  raw_ostream &OS, MCCodeEmitter *CE,
+                                  bool RelaxAll = false);
 
 } // end namespace llvm
 

lib/MC/MCAssembler.cpp

@@ -19,9 +19,9 @@
 #include "llvm/ADT/Statistic.h"
 #include "llvm/ADT/StringExtras.h"
 #include "llvm/ADT/Twine.h"
+#include "llvm/Support/Debug.h"
 #include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/raw_ostream.h"
-#include "llvm/Support/Debug.h"
 #include "llvm/Target/TargetRegistry.h"
 #include "llvm/Target/TargetAsmBackend.h"
 
@@ -30,11 +30,13 @@ using namespace llvm;
 
 namespace {
 namespace stats {
-STATISTIC(RelaxedInstructions, "Number of relaxed instructions");
-STATISTIC(RelaxationSteps, "Number of assembler layout and relaxation steps");
 STATISTIC(EmittedFragments, "Number of emitted assembler fragments");
 STATISTIC(EvaluateFixup, "Number of evaluated fixups");
+STATISTIC(FragmentLayouts, "Number of fragment layouts");
 STATISTIC(ObjectBytes, "Number of emitted object file bytes");
+STATISTIC(RelaxationSteps, "Number of assembler layout and relaxation steps");
+STATISTIC(RelaxedInstructions, "Number of relaxed instructions");
+STATISTIC(SectionLayouts, "Number of section layouts");
 }
 }
 
@@ -185,7 +187,7 @@ MCSymbolData::MCSymbolData(const MCSymbol &_Symbol, MCFragment *_Fragment,
 MCAssembler::MCAssembler(MCContext &_Context, TargetAsmBackend &_Backend,
                          MCCodeEmitter &_Emitter, raw_ostream &_OS)
   : Context(_Context), Backend(_Backend), Emitter(_Emitter),
-    OS(_OS), SubsectionsViaSymbols(false)
+    OS(_OS), RelaxAll(false), SubsectionsViaSymbols(false)
 {
 }
 
@@ -402,6 +404,8 @@ uint64_t MCAssembler::LayoutSection(MCSectionData &SD,
                                     uint64_t StartAddress) {
   bool IsVirtual = getBackend().isVirtualSection(SD.getSection());
 
+  ++stats::SectionLayouts;
+
   // Align this section if necessary by adding padding bytes to the previous
   // section. It is safe to adjust this out-of-band, because no symbol or
   // fragment is allowed to point past the end of the section at any time.
@@ -426,6 +430,8 @@ uint64_t MCAssembler::LayoutSection(MCSectionData &SD,
   for (MCSectionData::iterator it = SD.begin(), ie = SD.end(); it != ie; ++it) {
     MCFragment &F = *it;
 
+    ++stats::FragmentLayouts;
+
     uint64_t FragmentOffset = Address - StartAddress;
     Layout.setFragmentOffset(&F, FragmentOffset);
 
@@ -699,6 +705,9 @@ void MCAssembler::Finish() {
 bool MCAssembler::FixupNeedsRelaxation(const MCAsmFixup &Fixup,
                                        const MCFragment *DF,
                                        const MCAsmLayout &Layout) const {
+  if (getRelaxAll())
+    return true;
+
   // If we cannot resolve the fixup value, it requires relaxation.
   MCValue Target;
   uint64_t Value;
@@ -791,8 +800,11 @@ bool MCAssembler::LayoutOnce(MCAsmLayout &Layout) {
                                              F.getKind()));
       }
 
-      // Update the layout, and remember that we relaxed.
-      Layout.UpdateForSlide(IF, SlideAmount);
+      // Update the layout, and remember that we relaxed. If we are relaxing
+      // everything, we can skip this step since nothing will depend on updating
+      // the values.
+      if (!getRelaxAll())
+        Layout.UpdateForSlide(IF, SlideAmount);
       WasRelaxed = true;
     }
   }

lib/MC/MCMachOStreamer.cpp

@@ -75,6 +75,8 @@ public:
       CurSectionData(0) {}
   ~MCMachOStreamer() {}
 
+  MCAssembler &getAssembler() { return Assembler; }
+
   const MCExpr *AddValueSymbols(const MCExpr *Value) {
     switch (Value->getKind()) {
     case MCExpr::Target: assert(0 && "Can't handle target exprs yet!");
@@ -433,6 +435,10 @@ void MCMachOStreamer::Finish() {
 }
 
 MCStreamer *llvm::createMachOStreamer(MCContext &Context, TargetAsmBackend &TAB,
-                                      raw_ostream &OS, MCCodeEmitter *CE) {
-  return new MCMachOStreamer(Context, TAB, OS, CE);
+                                      raw_ostream &OS, MCCodeEmitter *CE,
+                                      bool RelaxAll) {
+  MCMachOStreamer *S = new MCMachOStreamer(Context, TAB, OS, CE);
+  if (RelaxAll)
+    S->getAssembler().setRelaxAll(true);
+  return S;
 }

tools/llvm-mc/llvm-mc.cpp

@@ -55,6 +55,9 @@ static cl::opt<unsigned>
 OutputAsmVariant("output-asm-variant",
                  cl::desc("Syntax variant to use for output printing"));
 
+static cl::opt<bool>
+RelaxAll("mc-relax-all", cl::desc("Relax all fixups"));
+
 enum OutputFileType {
   OFT_Null,
   OFT_AssemblyFile,
@@ -298,7 +301,7 @@ static int AssembleInput(const char *ProgName) {
     assert(FileType == OFT_ObjectFile && "Invalid file type!");
     CE.reset(TheTarget->createCodeEmitter(*TM, Ctx));
     TAB.reset(TheTarget->createAsmBackend(TripleName));
-    Str.reset(createMachOStreamer(Ctx, *TAB, *Out, CE.get()));
+    Str.reset(createMachOStreamer(Ctx, *TAB, *Out, CE.get(), RelaxAll));
   }
 
   AsmParser Parser(SrcMgr, Ctx, *Str.get(), *MAI);