Subzero: More asm-verbose fixes.

src/IceCfgNode.cpp

Index: src/IceCfgNode.cpp
diff --git a/src/IceCfgNode.cpp b/src/IceCfgNode.cpp
index 19c5d22d731879dff9ab258632028102dc234317..529e557e249a129cc234a89ddadabb2325b5f863 100644
--- a/src/IceCfgNode.cpp
+++ b/src/IceCfgNode.cpp
@@ -885,6 +885,10 @@ void CfgNode::emit(Cfg *Func) const {
   bool DecorateAsm =
       Liveness && Func->getContext()->getFlags().getDecorateAsm();
   Str << getAsmName() << ":\n";
+  // LiveRegCount keeps track of the number of currently live
+  // variables that each register is assigned to.  Normally that would
+  // be only 0 or 1, but the register allocator's AllowOverlap
+  // inference allows it to be greater than 1 for short periods.
   std::vector<SizeT> LiveRegCount(Func->getTarget()->getNumRegisters());
   if (DecorateAsm) {
     const bool IsLiveIn = true;
@@ -900,8 +904,21 @@ void CfgNode::emit(Cfg *Func) const {
   for (const Inst &I : Insts) {
     if (I.isDeleted())
       continue;
-    if (I.isRedundantAssign())
+    if (I.isRedundantAssign()) {
+      // Usually, redundant assignments end the live range of the src
+      // variable and begin the live range of the dest variable, with
+      // no net effect on the liveness of their register.  However, if
+      // the register allocator infers the AllowOverlap condition,
+      // then this may be a redundant assignment that does not end the
+      // src variable's live range, in which case the active variable
+      // count for that register needs to be bumped.  That normally
+      // would have happened as part of emitLiveRangesEnded(), but
+      // that isn't called for redundant assignments.
+      Variable *Dest = I.getDest();
+      if (DecorateAsm && Dest->hasReg() && !I.isLastUse(I.getSrc(0)))

[jvoung (off chromium), 2015/05/27 15:58:56]

Just checking -- this checks !I.isLastUse(I.getSrc(0)), and the code used to
sort of do that too, via the && before decrementing, but now the decrement
happens in emitLiveRangesEnded regardless of Instr->isLastUse(Var); so it looks
like for assignments with Dest == Src(0), the count is bumped on the Dest and
then decremented on the Src(0) also (in emitLiveRangesEnded)?

[Jim Stichnoth, 2015/05/27 16:08:55]

Sorry - I discovered that problem yesterday and uploaded a new patch this
morning that does indeed guard the decrement with an isLastUse() check.

+        ++LiveRegCount[Dest->getRegNum()];
       continue;
+    }
     I.emit(Func);
     if (DecorateAsm)
       emitLiveRangesEnded(Str, Func, &I, LiveRegCount);