[PATCH] [mips] Account for constant-zero operands in ADDE nodes.

[Vasileios Kalintiris]

Hi dsanders,

We identify the cases where the operand to an ADDE node is a constant
zero. In such cases, we can avoid generating an extra ADDu instruction
disguised as an identity move alias (ie. addu $r, $r, 0 --> move $r, $r).

http://reviews.llvm.org/D7906

Files:
  lib/Target/Mips/MipsSEISelDAGToDAG.cpp
  test/CodeGen/Mips/check-adde-redundant-moves.ll

Index: lib/Target/Mips/MipsSEISelDAGToDAG.cpp
===================================================================
--- lib/Target/Mips/MipsSEISelDAGToDAG.cpp
+++ lib/Target/Mips/MipsSEISelDAGToDAG.cpp
@@ -258,8 +258,12 @@
                                    CurDAG->getTargetConstant(Mips::sub_32, VT));
   }
 
-  SDNode *AddCarry = CurDAG->getMachineNode(ADDuOp, DL, VT,
-                                            SDValue(Carry, 0), RHS);
+  // Generate a second addition only if we know that RHS is not a
+  // constant-zero node.
+  SDNode *AddCarry = Carry;
+  ConstantSDNode *C = dyn_cast<ConstantSDNode>(RHS);
+  if (!C || C->getZExtValue())
+    AddCarry = CurDAG->getMachineNode(ADDuOp, DL, VT, SDValue(Carry, 0), RHS);
 
   return CurDAG->SelectNodeTo(Node, MOp, VT, MVT::Glue, LHS,
                               SDValue(AddCarry, 0));
Index: test/CodeGen/Mips/check-adde-redundant-moves.ll
===================================================================
--- /dev/null
+++ test/CodeGen/Mips/check-adde-redundant-moves.ll
@@ -0,0 +1,35 @@
+; RUN: llc < %s -march=mips -mcpu=mips2 | FileCheck %s \
+; RUN:    -check-prefix=ALL -check-prefix=GP32
+; RUN: llc < %s -march=mips -mcpu=mips32 | FileCheck %s \
+; RUN:    -check-prefix=ALL -check-prefix=GP32
+; RUN: llc < %s -march=mips -mcpu=mips32r2 | FileCheck %s \
+; RUN:    -check-prefix=ALL -check-prefix=GP32
+; RUN: llc < %s -march=mips -mcpu=mips32r3 | FileCheck %s \
+; RUN:    -check-prefix=ALL -check-prefix=GP32
+; RUN: llc < %s -march=mips -mcpu=mips32r5 | FileCheck %s \
+; RUN:    -check-prefix=ALL -check-prefix=GP32
+; RUN: llc < %s -march=mips -mcpu=mips32r6 | FileCheck %s \
+; RUN:    -check-prefix=ALL -check-prefix=GP32
+; RUN: llc < %s -march=mips64 -mcpu=mips3 | FileCheck %s -check-prefix=ALL
+; RUN: llc < %s -march=mips64 -mcpu=mips4 | FileCheck %s -check-prefix=ALL
+; RUN: llc < %s -march=mips64 -mcpu=mips64 | FileCheck %s -check-prefix=ALL
+; RUN: llc < %s -march=mips64 -mcpu=mips64r2 | FileCheck %s -check-prefix=ALL
+; RUN: llc < %s -march=mips64 -mcpu=mips64r3 | FileCheck %s -check-prefix=ALL
+; RUN: llc < %s -march=mips64 -mcpu=mips64r5 | FileCheck %s -check-prefix=ALL
+; RUN: llc < %s -march=mips64 -mcpu=mips64r6 | FileCheck %s -check-prefix=ALL
+
+define i64 @add_i64(i64 %a) {
+  ; GP32-LABEL: add_i64
+
+  ; GP32-NOT:    move $[[T0:[0-9]+]], $[[T0]]
+  %r = add i64 5, %a
+  ret i64 %r
+}
+
+define i128 @add_i128(i128 %a) {
+  ; ALL-LABEL: add_i128
+
+  ; ALL-NOT:    move $[[T0:[0-9]+]], $[[T0]]
+  %r = add i128 5, %a
+  ret i128 %r
+}

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