Index: llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
===================================================================
--- llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -7127,13 +7127,52 @@
             N2, APInt(N2.getScalarValueSizeInBits(), BitWidth - 1)))
       return IsFSHL ? N0 : N1;
 
-  // fold (fsh* N0, N1, c) -> (fsh* N0, N1, c % BitWidth)
+  auto IsUndefOrZero = [](SDValue V) {
+    if (V.isUndef())
+      return true;
+    if (ConstantSDNode *Cst = isConstOrConstSplat(V, /*AllowUndefs*/true))
+      return Cst->getAPIntValue() == 0;
+    return false;
+  };
+
   if (ConstantSDNode *Cst = isConstOrConstSplat(N2)) {
+    EVT ShAmtTy = N2.getValueType();
+
+    // fold (fsh* N0, N1, c) -> (fsh* N0, N1, c % BitWidth)
     if (Cst->getAPIntValue().uge(BitWidth)) {
       uint64_t RotAmt = Cst->getAPIntValue().urem(BitWidth);
       return DAG.getNode(N->getOpcode(), SDLoc(N), VT, N0, N1,
-                         DAG.getConstant(RotAmt, SDLoc(N), N2.getValueType()));
+                         DAG.getConstant(RotAmt, SDLoc(N), ShAmtTy));
     }
+
+    unsigned ShAmt = Cst->getZExtValue();
+    if (ShAmt == 0)
+      return IsFSHL ? N0 : N1;
+
+    // fold fshl(undef_or_zero, N1, C) -> lshr(N1, BW-C)
+    // fold fshr(undef_or_zero, N1, C) -> lshr(N1, C)
+    // fold fshl(N0, undef_or_zero, C) -> shl(N0, C)
+    // fold fshr(N0, undef_or_zero, C) -> shl(N0, BW-C)
+    if (IsUndefOrZero(N0))
+      return DAG.getNode(ISD::SRL, SDLoc(N), VT, N1,
+                         DAG.getConstant(IsFSHL ? BitWidth - ShAmt : ShAmt,
+                                         SDLoc(N), ShAmtTy));
+    if (IsUndefOrZero(N1))
+      return DAG.getNode(ISD::SHL, SDLoc(N), VT, N0,
+                         DAG.getConstant(IsFSHL ? ShAmt : BitWidth - ShAmt,
+                                         SDLoc(N), ShAmtTy));
+  }
+
+  // fold fshr(undef_or_zero, N1, N2) -> lshr(N1, N2)
+  // fold fshl(N0, undef_or_zero, N2) -> shl(N0, N2)
+  // iff We know the shift amount is in range.
+  // TODO: when is it worth doing SUB(BW, N2) as well?
+  if (isPowerOf2_32(BitWidth)) {
+    APInt ModuloBits(N2.getScalarValueSizeInBits(), BitWidth - 1);
+    if (IsUndefOrZero(N0) && !IsFSHL && DAG.MaskedValueIsZero(N2, ~ModuloBits))
+      return DAG.getNode(ISD::SRL, SDLoc(N), VT, N1, N2);
+    if (IsUndefOrZero(N1) && IsFSHL && DAG.MaskedValueIsZero(N2, ~ModuloBits))
+      return DAG.getNode(ISD::SHL, SDLoc(N), VT, N0, N2);
   }
 
   // fold (fshl N0, N0, N2) -> (rotl N0, N2)
Index: llvm/trunk/test/CodeGen/X86/funnel-shift.ll
===================================================================
--- llvm/trunk/test/CodeGen/X86/funnel-shift.ll
+++ llvm/trunk/test/CodeGen/X86/funnel-shift.ll
@@ -404,12 +404,13 @@
 ; X32-SSE2-LABEL: fshl_i32_undef0_cst:
 ; X32-SSE2:       # %bb.0:
 ; X32-SSE2-NEXT:    movl {{[0-9]+}}(%esp), %eax
-; X32-SSE2-NEXT:    shldl $9, %eax, %eax
+; X32-SSE2-NEXT:    shrl $23, %eax
 ; X32-SSE2-NEXT:    retl
 ;
 ; X64-AVX2-LABEL: fshl_i32_undef0_cst:
 ; X64-AVX2:       # %bb.0:
-; X64-AVX2-NEXT:    shldl $9, %edi, %eax
+; X64-AVX2-NEXT:    movl %edi, %eax
+; X64-AVX2-NEXT:    shrl $23, %eax
 ; X64-AVX2-NEXT:    retq
   %res = call i32 @llvm.fshl.i32(i32 undef, i32 %a0, i32 9)
   ret i32 %res
@@ -438,19 +439,18 @@
 ; X32-SSE2-LABEL: fshl_i32_undef1_msk:
 ; X32-SSE2:       # %bb.0:
 ; X32-SSE2-NEXT:    movl {{[0-9]+}}(%esp), %eax
-; X32-SSE2-NEXT:    movl {{[0-9]+}}(%esp), %ecx
-; X32-SSE2-NEXT:    andl $7, %ecx
-; X32-SSE2-NEXT:    # kill: def $cl killed $cl killed $ecx
-; X32-SSE2-NEXT:    shldl %cl, %eax, %eax
+; X32-SSE2-NEXT:    movb {{[0-9]+}}(%esp), %cl
+; X32-SSE2-NEXT:    andb $7, %cl
+; X32-SSE2-NEXT:    shll %cl, %eax
 ; X32-SSE2-NEXT:    retl
 ;
 ; X64-AVX2-LABEL: fshl_i32_undef1_msk:
 ; X64-AVX2:       # %bb.0:
 ; X64-AVX2-NEXT:    movl %esi, %ecx
 ; X64-AVX2-NEXT:    movl %edi, %eax
-; X64-AVX2-NEXT:    andl $7, %ecx
+; X64-AVX2-NEXT:    andb $7, %cl
 ; X64-AVX2-NEXT:    # kill: def $cl killed $cl killed $ecx
-; X64-AVX2-NEXT:    shldl %cl, %eax, %eax
+; X64-AVX2-NEXT:    shll %cl, %eax
 ; X64-AVX2-NEXT:    retq
   %m = and i32 %a1, 7
   %res = call i32 @llvm.fshl.i32(i32 %a0, i32 undef, i32 %m)
@@ -461,13 +461,13 @@
 ; X32-SSE2-LABEL: fshl_i32_undef1_cst:
 ; X32-SSE2:       # %bb.0:
 ; X32-SSE2-NEXT:    movl {{[0-9]+}}(%esp), %eax
-; X32-SSE2-NEXT:    shldl $9, %eax, %eax
+; X32-SSE2-NEXT:    shll $9, %eax
 ; X32-SSE2-NEXT:    retl
 ;
 ; X64-AVX2-LABEL: fshl_i32_undef1_cst:
 ; X64-AVX2:       # %bb.0:
 ; X64-AVX2-NEXT:    movl %edi, %eax
-; X64-AVX2-NEXT:    shldl $9, %eax, %eax
+; X64-AVX2-NEXT:    shll $9, %eax
 ; X64-AVX2-NEXT:    retq
   %res = call i32 @llvm.fshl.i32(i32 %a0, i32 undef, i32 9)
   ret i32 %res
@@ -513,19 +513,18 @@
 ; X32-SSE2-LABEL: fshr_i32_undef0_msk:
 ; X32-SSE2:       # %bb.0:
 ; X32-SSE2-NEXT:    movl {{[0-9]+}}(%esp), %eax
-; X32-SSE2-NEXT:    movl {{[0-9]+}}(%esp), %ecx
-; X32-SSE2-NEXT:    andl $7, %ecx
-; X32-SSE2-NEXT:    # kill: def $cl killed $cl killed $ecx
-; X32-SSE2-NEXT:    shrdl %cl, %eax, %eax
+; X32-SSE2-NEXT:    movb {{[0-9]+}}(%esp), %cl
+; X32-SSE2-NEXT:    andb $7, %cl
+; X32-SSE2-NEXT:    shrl %cl, %eax
 ; X32-SSE2-NEXT:    retl
 ;
 ; X64-AVX2-LABEL: fshr_i32_undef0_msk:
 ; X64-AVX2:       # %bb.0:
 ; X64-AVX2-NEXT:    movl %esi, %ecx
 ; X64-AVX2-NEXT:    movl %edi, %eax
-; X64-AVX2-NEXT:    andl $7, %ecx
+; X64-AVX2-NEXT:    andb $7, %cl
 ; X64-AVX2-NEXT:    # kill: def $cl killed $cl killed $ecx
-; X64-AVX2-NEXT:    shrdl %cl, %eax, %eax
+; X64-AVX2-NEXT:    shrl %cl, %eax
 ; X64-AVX2-NEXT:    retq
   %m = and i32 %a1, 7
   %res = call i32 @llvm.fshr.i32(i32 undef, i32 %a0, i32 %m)
@@ -536,13 +535,13 @@
 ; X32-SSE2-LABEL: fshr_i32_undef0_cst:
 ; X32-SSE2:       # %bb.0:
 ; X32-SSE2-NEXT:    movl {{[0-9]+}}(%esp), %eax
-; X32-SSE2-NEXT:    shrdl $9, %eax, %eax
+; X32-SSE2-NEXT:    shrl $9, %eax
 ; X32-SSE2-NEXT:    retl
 ;
 ; X64-AVX2-LABEL: fshr_i32_undef0_cst:
 ; X64-AVX2:       # %bb.0:
 ; X64-AVX2-NEXT:    movl %edi, %eax
-; X64-AVX2-NEXT:    shrdl $9, %eax, %eax
+; X64-AVX2-NEXT:    shrl $9, %eax
 ; X64-AVX2-NEXT:    retq
   %res = call i32 @llvm.fshr.i32(i32 undef, i32 %a0, i32 9)
   ret i32 %res
@@ -592,12 +591,13 @@
 ; X32-SSE2-LABEL: fshr_i32_undef1_cst:
 ; X32-SSE2:       # %bb.0:
 ; X32-SSE2-NEXT:    movl {{[0-9]+}}(%esp), %eax
-; X32-SSE2-NEXT:    shrdl $9, %eax, %eax
+; X32-SSE2-NEXT:    shll $23, %eax
 ; X32-SSE2-NEXT:    retl
 ;
 ; X64-AVX2-LABEL: fshr_i32_undef1_cst:
 ; X64-AVX2:       # %bb.0:
-; X64-AVX2-NEXT:    shrdl $9, %edi, %eax
+; X64-AVX2-NEXT:    movl %edi, %eax
+; X64-AVX2-NEXT:    shll $23, %eax
 ; X64-AVX2-NEXT:    retq
   %res = call i32 @llvm.fshr.i32(i32 %a0, i32 undef, i32 9)
   ret i32 %res
@@ -645,15 +645,14 @@
 define i32 @fshl_i32_zero0_cst(i32 %a0) nounwind {
 ; X32-SSE2-LABEL: fshl_i32_zero0_cst:
 ; X32-SSE2:       # %bb.0:
-; X32-SSE2-NEXT:    movl {{[0-9]+}}(%esp), %ecx
-; X32-SSE2-NEXT:    xorl %eax, %eax
-; X32-SSE2-NEXT:    shldl $9, %ecx, %eax
+; X32-SSE2-NEXT:    movl {{[0-9]+}}(%esp), %eax
+; X32-SSE2-NEXT:    shrl $23, %eax
 ; X32-SSE2-NEXT:    retl
 ;
 ; X64-AVX2-LABEL: fshl_i32_zero0_cst:
 ; X64-AVX2:       # %bb.0:
-; X64-AVX2-NEXT:    xorl %eax, %eax
-; X64-AVX2-NEXT:    shldl $9, %edi, %eax
+; X64-AVX2-NEXT:    movl %edi, %eax
+; X64-AVX2-NEXT:    shrl $23, %eax
 ; X64-AVX2-NEXT:    retq
   %res = call i32 @llvm.fshl.i32(i32 0, i32 %a0, i32 9)
   ret i32 %res
@@ -683,15 +682,14 @@
 define i32 @fshl_i32_zero1_cst(i32 %a0) nounwind {
 ; X32-SSE2-LABEL: fshl_i32_zero1_cst:
 ; X32-SSE2:       # %bb.0:
-; X32-SSE2-NEXT:    movl {{[0-9]+}}(%esp), %ecx
-; X32-SSE2-NEXT:    xorl %eax, %eax
-; X32-SSE2-NEXT:    shrdl $23, %ecx, %eax
+; X32-SSE2-NEXT:    movl {{[0-9]+}}(%esp), %eax
+; X32-SSE2-NEXT:    shll $9, %eax
 ; X32-SSE2-NEXT:    retl
 ;
 ; X64-AVX2-LABEL: fshl_i32_zero1_cst:
 ; X64-AVX2:       # %bb.0:
-; X64-AVX2-NEXT:    xorl %eax, %eax
-; X64-AVX2-NEXT:    shrdl $23, %edi, %eax
+; X64-AVX2-NEXT:    movl %edi, %eax
+; X64-AVX2-NEXT:    shll $9, %eax
 ; X64-AVX2-NEXT:    retq
   %res = call i32 @llvm.fshl.i32(i32 %a0, i32 0, i32 9)
   ret i32 %res
@@ -721,15 +719,14 @@
 define i32 @fshr_i32_zero0_cst(i32 %a0) nounwind {
 ; X32-SSE2-LABEL: fshr_i32_zero0_cst:
 ; X32-SSE2:       # %bb.0:
-; X32-SSE2-NEXT:    movl {{[0-9]+}}(%esp), %ecx
-; X32-SSE2-NEXT:    xorl %eax, %eax
-; X32-SSE2-NEXT:    shldl $23, %ecx, %eax
+; X32-SSE2-NEXT:    movl {{[0-9]+}}(%esp), %eax
+; X32-SSE2-NEXT:    shrl $9, %eax
 ; X32-SSE2-NEXT:    retl
 ;
 ; X64-AVX2-LABEL: fshr_i32_zero0_cst:
 ; X64-AVX2:       # %bb.0:
-; X64-AVX2-NEXT:    xorl %eax, %eax
-; X64-AVX2-NEXT:    shldl $23, %edi, %eax
+; X64-AVX2-NEXT:    movl %edi, %eax
+; X64-AVX2-NEXT:    shrl $9, %eax
 ; X64-AVX2-NEXT:    retq
   %res = call i32 @llvm.fshr.i32(i32 0, i32 %a0, i32 9)
   ret i32 %res
@@ -758,15 +755,14 @@
 define i32 @fshr_i32_zero1_cst(i32 %a0) nounwind {
 ; X32-SSE2-LABEL: fshr_i32_zero1_cst:
 ; X32-SSE2:       # %bb.0:
-; X32-SSE2-NEXT:    movl {{[0-9]+}}(%esp), %ecx
-; X32-SSE2-NEXT:    xorl %eax, %eax
-; X32-SSE2-NEXT:    shrdl $9, %ecx, %eax
+; X32-SSE2-NEXT:    movl {{[0-9]+}}(%esp), %eax
+; X32-SSE2-NEXT:    shll $23, %eax
 ; X32-SSE2-NEXT:    retl
 ;
 ; X64-AVX2-LABEL: fshr_i32_zero1_cst:
 ; X64-AVX2:       # %bb.0:
-; X64-AVX2-NEXT:    xorl %eax, %eax
-; X64-AVX2-NEXT:    shrdl $9, %edi, %eax
+; X64-AVX2-NEXT:    movl %edi, %eax
+; X64-AVX2-NEXT:    shll $23, %eax
 ; X64-AVX2-NEXT:    retq
   %res = call i32 @llvm.fshr.i32(i32 %a0, i32 0, i32 9)
   ret i32 %res