[ARM] Constant Materialize: imms with specific value can be encoded into mov.w

Summary: Thumb2 supports encoding immediates with specific patterns into mov.w by splatting the low 8 bits into other bytes.

Reviewers: john.brawn, jmolloy

Subscribers: jmolloy, aemerson, rengolin, samparker, llvm-commits

Differential Revision: https://reviews.llvm.org/D23090

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@277610 91177308-0d34-0410-b5e6-96231b3b80d8

Author: Weiming Zhao

lib/Target/ARM/ARMISelDAGToDAG.cpp

@@ -476,7 +476,9 @@ bool ARMDAGToDAGISel::isShifterOpProfitable(const SDValue &Shift,
 unsigned ARMDAGToDAGISel::ConstantMaterializationCost(unsigned Val) const {
   if (Subtarget->isThumb()) {
     if (Val <= 255) return 1;                               // MOV
-    if (Subtarget->hasV6T2Ops() && Val <= 0xffff) return 1; // MOVW
+    if (Subtarget->hasV6T2Ops() &&
+        (Val <= 0xffff || ARM_AM::getT2SOImmValSplatVal(Val) != -1))
+      return 1; // MOVW
     if (Val <= 510) return 2;                               // MOV + ADDi8
     if (~Val <= 255) return 2;                              // MOV + MVN
     if (ARM_AM::isThumbImmShiftedVal(Val)) return 2;        // MOV + LSL

test/CodeGen/ARM/subtarget-no-movt.ll

@@ -42,4 +42,21 @@ define i32 @foo1(i32 %a) {
   ret i32 %1
 }
 
+; NO-OPTION-LABEL: {{_?}}foo2
+; NO-OPTION: mov.w	r0, #-536813568
+; NO-OPTION-LABEL-NOT: .long
+
+; USE-MOVT-LABEL: {{_?}}foo2
+; USE-MOVT: mov.w	r0, #-536813568
+; USE-MOVT-NOT: .long
+
+; NO-USE-MOVT-LABEL: {{_?}}foo2
+; NO-USE-MOVT: mov.w	r0, #-536813568
+; NO-USE-MOVT-NOT: .long
+define i32 @foo2() {
+  %1 = load i32, i32* inttoptr (i32 -536813568 to i32*) ; load from 0xe000e000
+  ret i32 %1
+}
+
+
 attributes #0 = { "target-features"="+no-movt" }