Selectively invert ICMP operands for better address optimization

src/IceTargetLoweringX86BaseImpl.h

Index: src/IceTargetLoweringX86BaseImpl.h
diff --git a/src/IceTargetLoweringX86BaseImpl.h b/src/IceTargetLoweringX86BaseImpl.h
index a9dc7a7e75496b3d28fb654c2188c7b6cc2ed0da..f3a6e54bb3a9be3f7171495307ba9b30199aa4fe 100644
--- a/src/IceTargetLoweringX86BaseImpl.h
+++ b/src/IceTargetLoweringX86BaseImpl.h
@@ -5652,6 +5652,38 @@ void TargetX86Base<TraitsType>::lowerLoad(const InstLoad *Load) {
 }
 
 template <typename TraitsType>
+void TargetX86Base<TraitsType>::doAddressOptOther() {
+  // Inverts some Icmp instructions which helps doAddressOptLoad later.
+  Inst *Instr = Context.getCur();
+  auto *VMetadata = Func->getVMetadata();
+  if (auto *Icmp = llvm::dyn_cast<InstIcmp>(Instr)) {
+    if (llvm::isa<Constant>(Icmp->getSrc(0)) ||
+        llvm::isa<Constant>(Icmp->getSrc(1)))
+      return;
+    auto *Var0 = llvm::dyn_cast<Variable>(Icmp->getSrc(0));

[Jim Stichnoth, 2016/07/14 19:10:02]

As we discussed offline, it seems like the conditions on Src0 and Src1 are (or
should be) essentially identical, so it would be nice to have a helper function
that is called twice.

We want to reverse the condition/operands when Src0 derives from a load
instruction, and Src1 does not derive from a load instruction.

+    if (Var0 == nullptr)
+      return;
+    if (!VMetadata->isTracked(Var0))
+      return;
+    auto *Op0Def = VMetadata->getFirstDefinitionSingleBlock(Var0);
+    if (Op0Def == nullptr || !llvm::isa<InstLoad>(Op0Def))
+      return;
+    if (VMetadata->getLocalUseNode(Var0) != Context.getNode())
+      return;
+
+    auto *Var1 = llvm::dyn_cast<Variable>(Icmp->getSrc(1));
+    if (Var1 != nullptr && VMetadata->isTracked(Var1)) {
+      auto *Op1Def = VMetadata->getFirstDefinitionSingleBlock(Var1);
+      if (Op1Def != nullptr && !VMetadata->isMultiBlock(Var1) &&
+          llvm::isa<InstLoad>(Op1Def)) {
+        return; // Both are loads
+      }
+    }
+    Icmp->reverseConditionAndOperands();
+  }
+}
+
+template <typename TraitsType>
 void TargetX86Base<TraitsType>::doAddressOptLoad() {
   Inst *Instr = Context.getCur();
   Operand *Addr = Instr->getSrc(0);