Re-apply the change from r191393 with fix for pr17380.

This change fixes the problem reported in pr17380 and re-add the dagcombine 
transformation ensuring that the value types are always legal if the 
transformation is triggered after Legalization took place.

Added the test case from pr17380.

llvm-svn: 191509

2 files changed, 223 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index d5f3e9c53e2..f9458925885 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -3748,6 +3748,26 @@ SDValue DAGCombiner::visitSHL(SDNode *N) {
     }
   }
 
+  // fold (shl (zext (srl x, C)), C) -> (zext (shl (srl x, C), C))
+  // Only fold this if the inner zext has no other uses to avoid increasing
+  // the total number of instructions.
+  if (N1C && N0.getOpcode() == ISD::ZERO_EXTEND && N0.hasOneUse() &&
+      N0.getOperand(0).getOpcode() == ISD::SRL &&
+      isa<ConstantSDNode>(N0.getOperand(0)->getOperand(1))) {
+    uint64_t c1 =
+      cast<ConstantSDNode>(N0.getOperand(0)->getOperand(1))->getZExtValue();
+    if (c1 < VT.getSizeInBits()) {
+      uint64_t c2 = N1C->getZExtValue();
+      if (c1 == c2) {
+        SDValue NewOp0 = N0.getOperand(0);
+        EVT CountVT = NewOp0.getOperand(1).getValueType();
+        SDValue NewSHL = DAG.getNode(ISD::SHL, SDLoc(N), NewOp0.getValueType(),
+                                     NewOp0, DAG.getConstant(c2, CountVT));
+        return DAG.getNode(ISD::ZERO_EXTEND, SDLoc(N0), VT, NewSHL);
+      }
+    }
+  }
+
   // fold (shl (srl x, c1), c2) -> (and (shl x, (sub c2, c1), MASK) or
   //                               (and (srl x, (sub c1, c2), MASK)
   // Only fold this if the inner shift has no other uses -- if it does, folding
diff --git a/llvm/test/CodeGen/X86/dagcombine-shifts.ll b/llvm/test/CodeGen/X86/dagcombine-shifts.ll
new file mode 100644
index 00000000000..aed3550a9af
--- /dev/null
+++ b/llvm/test/CodeGen/X86/dagcombine-shifts.ll
@@ -0,0 +1,203 @@
+; SCE: bug 39153
+
+; RUN: llc < %s -mtriple=x86_64-linux-gnu | FileCheck %s
+
+; fold (shl (zext (lshr (A, X))), X) -> (zext (shl (lshr (A, X)), X))
+
+; Canolicalize the sequence shl/zext/lshr performing the zeroextend
+; as the last instruction of the sequence.
+; This will help DAGCombiner to identify and then fold the sequence
+; of shifts into a single AND.
+; This transformation is profitable if the shift amounts are the same
+; and if there is only one use of the zext.
+
+define i16 @fun1(i8 zeroext %v) {
+entry:
+  %shr = lshr i8 %v, 4
+  %ext = zext i8 %shr to i16
+  %shl = shl i16 %ext, 4
+  ret i16 %shl
+}
+
+; CHECK-LABEL: @fun1
+; CHECK: and
+; CHECK-NOT: shr
+; CHECK-NOT: shl
+; CHECK: ret
+
+define i32 @fun2(i8 zeroext %v) {
+entry:
+  %shr = lshr i8 %v, 4
+  %ext = zext i8 %shr to i32
+  %shl = shl i32 %ext, 4
+  ret i32 %shl
+}
+
+; CHECK-LABEL: @fun2
+; CHECK: and
+; CHECK-NOT: shr
+; CHECK-NOT: shl
+; CHECK: ret
+
+define i32 @fun3(i16 zeroext %v) {
+entry:
+  %shr = lshr i16 %v, 4
+  %ext = zext i16 %shr to i32
+  %shl = shl i32 %ext, 4
+  ret i32 %shl
+}
+
+; CHECK-LABEL: @fun3
+; CHECK: and
+; CHECK-NOT: shr
+; CHECK-NOT: shl
+; CHECK: ret
+
+define i64 @fun4(i8 zeroext %v) {
+entry:
+  %shr = lshr i8 %v, 4
+  %ext = zext i8 %shr to i64
+  %shl = shl i64 %ext, 4
+  ret i64 %shl
+}
+
+; CHECK-LABEL: @fun4
+; CHECK: and
+; CHECK-NOT: shr
+; CHECK-NOT: shl
+; CHECK: ret
+
+define i64 @fun5(i16 zeroext %v) {
+entry:
+  %shr = lshr i16 %v, 4
+  %ext = zext i16 %shr to i64
+  %shl = shl i64 %ext, 4
+  ret i64 %shl
+}
+
+; CHECK-LABEL: @fun5
+; CHECK: and
+; CHECK-NOT: shr
+; CHECK-NOT: shl
+; CHECK: ret
+
+define i64 @fun6(i32 zeroext %v) {
+entry:
+  %shr = lshr i32 %v, 4
+  %ext = zext i32 %shr to i64
+  %shl = shl i64 %ext, 4
+  ret i64 %shl
+}
+
+; CHECK-LABEL: @fun6
+; CHECK: and
+; CHECK-NOT: shr
+; CHECK-NOT: shl
+; CHECK: ret
+
+; Don't fold the pattern if we use arithmetic shifts.
+
+define i64 @fun7(i8 zeroext %v) {
+entry:
+  %shr = ashr i8 %v, 4
+  %ext = zext i8 %shr to i64
+  %shl = shl i64 %ext, 4
+  ret i64 %shl
+}
+
+; CHECK-LABEL: @fun7
+; CHECK: sar
+; CHECK: shl
+; CHECK: ret
+
+define i64 @fun8(i16 zeroext %v) {
+entry:
+  %shr = ashr i16 %v, 4
+  %ext = zext i16 %shr to i64
+  %shl = shl i64 %ext, 4
+  ret i64 %shl
+}
+
+; CHECK-LABEL: @fun8
+; CHECK: sar
+; CHECK: shl
+; CHECK: ret
+
+define i64 @fun9(i32 zeroext %v) {
+entry:
+  %shr = ashr i32 %v, 4
+  %ext = zext i32 %shr to i64
+  %shl = shl i64 %ext, 4
+  ret i64 %shl
+}
+
+; CHECK-LABEL: @fun9
+; CHECK: sar
+; CHECK: shl
+; CHECK: ret
+
+; Don't fold the pattern if there is more than one use of the
+; operand in input to the shift left.
+
+define i64 @fun10(i8 zeroext %v) {
+entry:
+  %shr = lshr i8 %v, 4
+  %ext = zext i8 %shr to i64
+  %shl = shl i64 %ext, 4
+  %add = add i64 %shl, %ext
+  ret i64 %add
+}
+
+; CHECK-LABEL: @fun10
+; CHECK: shr
+; CHECK: shl
+; CHECK: ret
+
+define i64 @fun11(i16 zeroext %v) {
+entry:
+  %shr = lshr i16 %v, 4
+  %ext = zext i16 %shr to i64
+  %shl = shl i64 %ext, 4
+  %add = add i64 %shl, %ext
+  ret i64 %add
+}
+
+; CHECK-LABEL: @fun11
+; CHECK: shr
+; CHECK: shl
+; CHECK: ret
+
+define i64 @fun12(i32 zeroext %v) {
+entry:
+  %shr = lshr i32 %v, 4
+  %ext = zext i32 %shr to i64
+  %shl = shl i64 %ext, 4
+  %add = add i64 %shl, %ext
+  ret i64 %add
+}
+
+; CHECK-LABEL: @fun12
+; CHECK: shr
+; CHECK: shl
+; CHECK: ret
+
+; PR17380
+; Make sure that the combined dags are legal if we run the DAGCombiner after
+; Legalization took place. The add instruction is redundant and increases by 
+; one the number of uses of the zext. This prevents the transformation from
+; firing before dags are legalized and optimized.
+; Once the add is removed, the number of uses becomes one and therefore the
+; dags are canonicalized. After Legalization, we need to make sure that the
+; valuetype for the shift count is legal.
+
+define void @g(i32 %a) {
+  %b = lshr i32 %a, 2
+  %c = zext i32 %b to i64
+  %d = add i64 %c, 1
+  %e = shl i64 %c, 2
+  tail call void @f(i64 %e)
+  ret void
+}
+
+declare void @f(i64)
+