[MC] Pass MCSubtargetInfo to fixupNeedsRelaxation and applyFixup

On targets like Arm some relaxations may only be performed when certain
architectural features are available. As functions can be compiled with
differing levels of architectural support we must make a judgement on
whether we can relax based on the MCSubtargetInfo for the function. This
change passes through the MCSubtargetInfo for the function to
fixupNeedsRelaxation so that the decision on whether to relax can be made
per function. In this patch, only the ARM backend makes use of this
information. We must also pass the MCSubtargetInfo to applyFixup because
some fixups skip error checking on the assumption that relaxation has
occurred, to prevent code-generation errors applyFixup must see the same
MCSubtargetInfo as fixupNeedsRelaxation.

Differential Revision: https://reviews.llvm.org/D44928

llvm-svn: 334078

1 files changed, 21 insertions, 8 deletions

diff --git a/llvm/lib/MC/MCObjectStreamer.cpp b/llvm/lib/MC/MCObjectStreamer.cpp
index 3ed9a6fbf6b..5159cfee7a8 100644
--- a/llvm/lib/MC/MCObjectStreamer.cpp
+++ b/llvm/lib/MC/MCObjectStreamer.cpp
@@ -146,12 +146,24 @@ MCFragment *MCObjectStreamer::getCurrentFragment() const {
   return nullptr;
 }
 
-MCDataFragment *MCObjectStreamer::getOrCreateDataFragment() {
-  MCDataFragment *F = dyn_cast_or_null<MCDataFragment>(getCurrentFragment());
+static bool CanReuseDataFragment(const MCDataFragment &F,
+                                 const MCAssembler &Assembler,
+                                 const MCSubtargetInfo *STI) {
+  if (!F.hasInstructions())
+    return true;
   // When bundling is enabled, we don't want to add data to a fragment that
   // already has instructions (see MCELFStreamer::EmitInstToData for details)
-  if (!F || (Assembler->isBundlingEnabled() && !Assembler->getRelaxAll() &&
-             F->hasInstructions())) {
+  if (Assembler.isBundlingEnabled())
+    return Assembler.getRelaxAll();
+  // If the subtarget is changed mid fragment we start a new fragment to record
+  // the new STI.
+  return !STI || F.getSubtargetInfo() == STI;
+}
+
+MCDataFragment *
+MCObjectStreamer::getOrCreateDataFragment(const MCSubtargetInfo *STI) {
+  MCDataFragment *F = dyn_cast_or_null<MCDataFragment>(getCurrentFragment());
+  if (!F || !CanReuseDataFragment(*F, *Assembler, STI)) {
     F = new MCDataFragment();
     insert(F);
   }
@@ -327,7 +339,7 @@ void MCObjectStreamer::EmitInstructionImpl(const MCInst &Inst,
 
   // If this instruction doesn't need relaxation, just emit it as data.
   MCAssembler &Assembler = getAssembler();
-  if (!Assembler.getBackend().mayNeedRelaxation(Inst)) {
+  if (!Assembler.getBackend().mayNeedRelaxation(Inst, STI)) {
     EmitInstToData(Inst, STI);
     return;
   }
@@ -341,7 +353,7 @@ void MCObjectStreamer::EmitInstructionImpl(const MCInst &Inst,
       (Assembler.isBundlingEnabled() && Sec->isBundleLocked())) {
     MCInst Relaxed;
     getAssembler().getBackend().relaxInstruction(Inst, STI, Relaxed);
-    while (getAssembler().getBackend().mayNeedRelaxation(Relaxed))
+    while (getAssembler().getBackend().mayNeedRelaxation(Relaxed, STI))
       getAssembler().getBackend().relaxInstruction(Relaxed, STI, Relaxed);
     EmitInstToData(Relaxed, STI);
     return;
@@ -606,7 +618,8 @@ void MCObjectStreamer::EmitGPRel64Value(const MCExpr *Value) {
 }
 
 bool MCObjectStreamer::EmitRelocDirective(const MCExpr &Offset, StringRef Name,
-                                          const MCExpr *Expr, SMLoc Loc) {
+                                          const MCExpr *Expr, SMLoc Loc,
+                                          const MCSubtargetInfo &STI) {
   int64_t OffsetValue;
   if (!Offset.evaluateAsAbsolute(OffsetValue))
     llvm_unreachable("Offset is not absolute");
@@ -614,7 +627,7 @@ bool MCObjectStreamer::EmitRelocDirective(const MCExpr &Offset, StringRef Name,
   if (OffsetValue < 0)
     llvm_unreachable("Offset is negative");
 
-  MCDataFragment *DF = getOrCreateDataFragment();
+  MCDataFragment *DF = getOrCreateDataFragment(&STI);
   flushPendingLabels(DF, DF->getContents().size());
 
   Optional<MCFixupKind> MaybeKind = Assembler->getBackend().getFixupKind(Name);