[X86] Don't accidentally select shll $1, %eax when shrinking an immediate.

addl has higher throughput and this was needlessly picking a suboptimal
encoding causing PR23098.

I wish there was a way of doing this without further duplicating tbl-
generated patterns, but so far I haven't found one.

llvm-svn: 233832

2 files changed, 29 insertions, 1 deletions

diff --git a/llvm/lib/Target/X86/X86ISelDAGToDAG.cpp b/llvm/lib/Target/X86/X86ISelDAGToDAG.cpp
index fb12ce51db2..5da7acfc6ef 100644
--- a/llvm/lib/Target/X86/X86ISelDAGToDAG.cpp
+++ b/llvm/lib/Target/X86/X86ISelDAGToDAG.cpp
@@ -2187,7 +2187,7 @@ SDNode *X86DAGToDAGISel::Select(SDNode *Node) {
     if (Opcode != ISD::AND && (Val & RemovedBitsMask) != 0)
       break;
 
-    unsigned ShlOp, Op;
+    unsigned ShlOp, AddOp, Op;
     MVT CstVT = NVT;
 
     // Check the minimum bitwidth for the new constant.
@@ -2208,6 +2208,7 @@ SDNode *X86DAGToDAGISel::Select(SDNode *Node) {
     case MVT::i32:
       assert(CstVT == MVT::i8);
       ShlOp = X86::SHL32ri;
+      AddOp = X86::ADD32rr;
 
       switch (Opcode) {
       default: llvm_unreachable("Impossible opcode");
@@ -2219,6 +2220,7 @@ SDNode *X86DAGToDAGISel::Select(SDNode *Node) {
     case MVT::i64:
       assert(CstVT == MVT::i8 || CstVT == MVT::i32);
       ShlOp = X86::SHL64ri;
+      AddOp = X86::ADD64rr;
 
       switch (Opcode) {
       default: llvm_unreachable("Impossible opcode");
@@ -2232,6 +2234,9 @@ SDNode *X86DAGToDAGISel::Select(SDNode *Node) {
     // Emit the smaller op and the shift.
     SDValue NewCst = CurDAG->getTargetConstant(Val >> ShlVal, CstVT);
     SDNode *New = CurDAG->getMachineNode(Op, dl, NVT, N0->getOperand(0),NewCst);
+    if (ShlVal == 1)
+      return CurDAG->SelectNodeTo(Node, AddOp, NVT, SDValue(New, 0),
+                                  SDValue(New, 0));
     return CurDAG->SelectNodeTo(Node, ShlOp, NVT, SDValue(New, 0),
                                 getI8Imm(ShlVal));
   }
diff --git a/llvm/test/CodeGen/X86/narrow-shl-cst.ll b/llvm/test/CodeGen/X86/narrow-shl-cst.ll
index 40b976014a7..c9e9a3d2a97 100644
--- a/llvm/test/CodeGen/X86/narrow-shl-cst.ll
+++ b/llvm/test/CodeGen/X86/narrow-shl-cst.ll
@@ -99,3 +99,26 @@ define i64 @test11(i64 %x) nounwind {
 ; CHECK: xorq $-65536
 ; CHECK: shlq $33
 }
+
+; PR23098
+define i32 @test12(i32 %x, i32* %y) nounwind {
+  %and = shl i32 %x, 1
+  %shl = and i32 %and, 255
+  store i32 %shl, i32* %y
+  ret i32 %shl
+; CHECK-LABEL: test12:
+; CHECK: andl $127
+; CHECK-NEXT: addl
+; CHECK-NOT: shl
+}
+
+define i64 @test13(i64 %x, i64* %y) nounwind {
+  %and = shl i64 %x, 1
+  %shl = and i64 %and, 255
+  store i64 %shl, i64* %y
+  ret i64 %shl
+; CHECK-LABEL: test13:
+; CHECK: andq $127
+; CHECK-NEXT: addq
+; CHECK-NOT: shl
+}