From 47801092543718562306dd485cd334fb25a95d67 Mon Sep 17 00:00:00 2001
From: Richard Osborne <richard@xmos.com>
Date: Thu, 11 Mar 2010 16:26:35 +0000
Subject: [PATCH] Add dag combine to simplify lmul(x, 0, a, b)

llvm-svn: 98258
---
 llvm/lib/Target/XCore/XCoreISelLowering.cpp | 27 +++++++++++++++++++++
 llvm/test/CodeGen/XCore/mul64.ll            | 13 ++++++++++
 2 files changed, 40 insertions(+)

diff --git a/llvm/lib/Target/XCore/XCoreISelLowering.cpp b/llvm/lib/Target/XCore/XCoreISelLowering.cpp
index 7cbfe3edc69e..bf1a45762795 100644
--- a/llvm/lib/Target/XCore/XCoreISelLowering.cpp
+++ b/llvm/lib/Target/XCore/XCoreISelLowering.cpp
@@ -1345,6 +1345,33 @@ SDValue XCoreTargetLowering::PerformDAGCombine(SDNode *N,
     }
   }
   break;
+  case XCoreISD::LMUL: {
+    SDValue N0 = N->getOperand(0);
+    SDValue N1 = N->getOperand(1);
+    SDValue N2 = N->getOperand(2);
+    SDValue N3 = N->getOperand(3);
+    ConstantSDNode *N0C = dyn_cast<ConstantSDNode>(N0);
+    ConstantSDNode *N1C = dyn_cast<ConstantSDNode>(N1);
+    EVT VT = N0.getValueType();
+    // Canonicalize multiplicative constant to RHS. If both multiplicative
+    // operands are constant canonicalize smallest to RHS.
+    if ((N0C && !N1C) ||
+        (N0C && N1C && N0C->getZExtValue() < N1C->getZExtValue()))
+      return DAG.getNode(XCoreISD::LMUL, dl, DAG.getVTList(VT, VT), N1, N0, N2, N3);
+
+    // lmul(x, 0, a, b)
+    if (N1C && N1C->isNullValue()) {
+      // If the high result is unused fold to add(a, b)
+      if (N->hasNUsesOfValue(0, 0)) {
+        SDValue Lo = DAG.getNode(ISD::ADD, dl, VT, N2, N3);
+        SDValue Ops [] = { Lo, Lo };
+        return DAG.getMergeValues(Ops, 2, dl);
+      }
+      // Otherwise fold to ladd(a, b, 0)
+      return DAG.getNode(XCoreISD::LADD, dl, DAG.getVTList(VT, VT), N2, N3, N1);
+    }
+  }
+  break;
   case ISD::ADD: {
     // Fold 32 bit expressions such as add(add(mul(x,y),a),b) ->
     // lmul(x, y, a, b). The high result of lmul will be ignored.
diff --git a/llvm/test/CodeGen/XCore/mul64.ll b/llvm/test/CodeGen/XCore/mul64.ll
index 329e214d1d23..1dc94712507e 100644
--- a/llvm/test/CodeGen/XCore/mul64.ll
+++ b/llvm/test/CodeGen/XCore/mul64.ll
@@ -37,3 +37,16 @@ entry:
 ; CHECK-NEXT: mul r0, r0, r3
 ; CHECK-NEXT: lmul r0, r1, r1, r2, r11, r0
 ; CHECK-NEXT: mov r0, r4
+
+define i64 @mul64_2(i64 %a, i32 %b) {
+entry:
+	%0 = zext i32 %b to i64
+	%1 = mul i64 %a, %0
+	ret i64 %1
+}
+; CHECK: mul64_2:
+; CHECK: ldc r3, 0
+; CHECK-NEXT: lmul r3, r0, r0, r2, r3, r3
+; CHECK-NEXT: mul r1, r1, r2
+; CHECK-NEXT: add r1, r3, r1
+; CHECK-NEXT: retsp 0