Perform mul combine when multiplying wiht negative constants.

Patch by Weiming Zhao!
This fixes PR12212

llvm-svn: 153049

1 files changed, 48 insertions, 18 deletions

diff --git a/llvm/lib/Target/ARM/ARMISelLowering.cpp b/llvm/lib/Target/ARM/ARMISelLowering.cpp
index 459d82cdbe9..e26dd22c929 100644
--- a/llvm/lib/Target/ARM/ARMISelLowering.cpp
+++ b/llvm/lib/Target/ARM/ARMISelLowering.cpp
@@ -6865,33 +6865,63 @@ static SDValue PerformMULCombine(SDNode *N,
   if (!C)
     return SDValue();
 
-  uint64_t MulAmt = C->getZExtValue();
+  int64_t MulAmt = C->getSExtValue();
   unsigned ShiftAmt = CountTrailingZeros_64(MulAmt);
+
   ShiftAmt = ShiftAmt & (32 - 1);
   SDValue V = N->getOperand(0);
   DebugLoc DL = N->getDebugLoc();
 
   SDValue Res;
   MulAmt >>= ShiftAmt;
-  if (isPowerOf2_32(MulAmt - 1)) {
-    // (mul x, 2^N + 1) => (add (shl x, N), x)
-    Res = DAG.getNode(ISD::ADD, DL, VT,
-                      V, DAG.getNode(ISD::SHL, DL, VT,
-                                     V, DAG.getConstant(Log2_32(MulAmt-1),
-                                                        MVT::i32)));
-  } else if (isPowerOf2_32(MulAmt + 1)) {
-    // (mul x, 2^N - 1) => (sub (shl x, N), x)
-    Res = DAG.getNode(ISD::SUB, DL, VT,
-                      DAG.getNode(ISD::SHL, DL, VT,
-                                  V, DAG.getConstant(Log2_32(MulAmt+1),
-                                                     MVT::i32)),
-                                                     V);
-  } else
-    return SDValue();
+
+  if (MulAmt >= 0) {
+    if (isPowerOf2_32(MulAmt - 1)) {
+      // (mul x, 2^N + 1) => (add (shl x, N), x)
+      Res = DAG.getNode(ISD::ADD, DL, VT,
+                        V,
+                        DAG.getNode(ISD::SHL, DL, VT,
+                                    V,
+                                    DAG.getConstant(Log2_32(MulAmt - 1),
+                                                    MVT::i32)));
+    } else if (isPowerOf2_32(MulAmt + 1)) {
+      // (mul x, 2^N - 1) => (sub (shl x, N), x)
+      Res = DAG.getNode(ISD::SUB, DL, VT,
+                        DAG.getNode(ISD::SHL, DL, VT,
+                                    V,
+                                    DAG.getConstant(Log2_32(MulAmt + 1),
+                                                    MVT::i32)),
+                        V);
+    } else
+      return SDValue();
+  } else {
+    uint64_t MulAmtAbs = -MulAmt;
+    if (isPowerOf2_32(MulAmtAbs + 1)) {
+      // (mul x, -(2^N - 1)) => (sub x, (shl x, N))
+      Res = DAG.getNode(ISD::SUB, DL, VT,
+                        V,
+                        DAG.getNode(ISD::SHL, DL, VT,
+                                    V,
+                                    DAG.getConstant(Log2_32(MulAmtAbs + 1),
+                                                    MVT::i32)));
+    } else if (isPowerOf2_32(MulAmtAbs - 1)) {
+      // (mul x, -(2^N + 1)) => - (add (shl x, N), x)
+      Res = DAG.getNode(ISD::ADD, DL, VT,
+                        V,
+                        DAG.getNode(ISD::SHL, DL, VT,
+                                    V,
+                                    DAG.getConstant(Log2_32(MulAmtAbs-1),
+                                                    MVT::i32)));
+      Res = DAG.getNode(ISD::SUB, DL, VT,
+                        DAG.getConstant(0, MVT::i32),Res);
+
+    } else
+      return SDValue();
+  }
 
   if (ShiftAmt != 0)
-    Res = DAG.getNode(ISD::SHL, DL, VT, Res,
-                      DAG.getConstant(ShiftAmt, MVT::i32));
+    Res = DAG.getNode(ISD::SHL, DL, VT,
+                      Res, DAG.getConstant(ShiftAmt, MVT::i32));
 
   // Do not add new nodes to DAG combiner worklist.
   DCI.CombineTo(N, Res, false);