Subzero: Fix address mode optimization involving phi temporaries.

src/IceTargetLoweringX8632.cpp

Index: src/IceTargetLoweringX8632.cpp
diff --git a/src/IceTargetLoweringX8632.cpp b/src/IceTargetLoweringX8632.cpp
index 7ed8abff5152680166ca35fe06b044d8211f19c7..a0e440892bf7ef923494b918b3680a18a2d6206e 100644
--- a/src/IceTargetLoweringX8632.cpp
+++ b/src/IceTargetLoweringX8632.cpp
@@ -3482,8 +3482,35 @@ bool isAdd(const Inst *Inst) {
   return false;
 }
 
-void computeAddressOpt(Variable *&Base, Variable *&Index, uint16_t &Shift,
-                       int32_t &Offset) {
+void dumpAddressOpt(const Cfg *Func, const Variable *Base,
+                    const Variable *Index, uint16_t Shift, int32_t Offset,
+                    const Inst *Reason) {
+  if (!Func->getContext()->isVerbose(IceV_AddrOpt))
+    return;
+  Ostream &Str = Func->getContext()->getStrDump();
+  Str << "Instruction: ";
+  Reason->dumpDecorated(Func);
+  Str << "  results in Base=";
+  if (Base)
+    Base->dump(Func);
+  else
+    Str << "<null>";
+  Str << ", Index=";
+  if (Index)
+    Index->dump(Func);
+  else
+    Str << "<null>";
+  Str << ", Shift=" << Shift << ", Offset=" << Offset << "\n";
+}
+
+void computeAddressOpt(Cfg *Func, const Inst *Instr, Variable *&Base,
+                       Variable *&Index, uint16_t &Shift, int32_t &Offset) {
+  Func->setCurrentNode(NULL);
+  if (Func->getContext()->isVerbose(IceV_AddrOpt)) {
+    Ostream &Str = Func->getContext()->getStrDump();
+    Str << "\nStarting computeAddressOpt for instruction:\n  ";
+    Instr->dumpDecorated(Func);
+  }
   (void)Offset; // TODO: pattern-match for non-zero offsets.
   if (Base == NULL)
     return;
@@ -3506,6 +3533,7 @@ void computeAddressOpt(Variable *&Base, Variable *&Index, uint16_t &Shift,
         // TODO: ensure BaseVariable0 stays single-BB

[jvoung (off chromium), 2014/08/27 16:21:07]

Does this take care of the TODO?

Maybe not the one below, because that's assuming the BaseInst is an add instead
of an assign.

[Jim Stichnoth, 2014/08/27 20:23:14]

I don't think so.  This needs to be tuned, but my feeling about address mode
optimization is to try to avoid using variables in the expression that are
defined far away, because that may increase register pressure.  Single-BB is an
approximation for defined not far away.

         true) {
       Base = BaseVariable0;
+      dumpAddressOpt(Func, Base, Index, Shift, Offset, BaseInst);
       continue;
     }
 
@@ -3523,6 +3551,7 @@ void computeAddressOpt(Variable *&Base, Variable *&Index, uint16_t &Shift,
       Base = BaseVariable0;
       Index = BaseVariable1;
       Shift = 0; // should already have been 0
+      dumpAddressOpt(Func, Base, Index, Shift, Offset, BaseInst);
       continue;
     }
 
@@ -3560,6 +3589,7 @@ void computeAddressOpt(Variable *&Base, Variable *&Index, uint16_t &Shift,
         if (Shift + LogMult <= 3) {
           Index = IndexVariable0;
           Shift += LogMult;
+          dumpAddressOpt(Func, Base, Index, Shift, Offset, IndexInst);
           continue;
         }
       }
@@ -3589,6 +3619,7 @@ void computeAddressOpt(Variable *&Base, Variable *&Index, uint16_t &Shift,
       }
       Base = Var;
       Offset += IsAdd ? Const->getValue() : -Const->getValue();
+      dumpAddressOpt(Func, Base, Index, Shift, Offset, BaseInst);
       continue;
     }
 
@@ -3684,7 +3715,7 @@ void TargetX8632::doAddressOptLoad() {
   const OperandX8632Mem::SegmentRegisters SegmentReg =
       OperandX8632Mem::DefaultSegment;
   Variable *Base = llvm::dyn_cast<Variable>(Addr);
-  computeAddressOpt(Base, Index, Shift, Offset);
+  computeAddressOpt(Func, Inst, Base, Index, Shift, Offset);
   if (Base && Addr != Base) {
     Constant *OffsetOp = Ctx->getConstantInt(IceType_i32, Offset);
     Addr = OperandX8632Mem::create(Func, Dest->getType(), Base, OffsetOp, Index,
@@ -3866,7 +3897,7 @@ void TargetX8632::doAddressOptStore() {
   // registers there either.
   const OperandX8632Mem::SegmentRegisters SegmentReg =
       OperandX8632Mem::DefaultSegment;
-  computeAddressOpt(Base, Index, Shift, Offset);
+  computeAddressOpt(Func, Inst, Base, Index, Shift, Offset);
   if (Base && Addr != Base) {
     Constant *OffsetOp = Ctx->getConstantInt(IceType_i32, Offset);
     Addr = OperandX8632Mem::create(Func, Data->getType(), Base, OffsetOp, Index,