[ARM GlobalISel] Import MOVi32imm into GlobalISel

rovka · rovka · commit 8987d00653a1 · 2019-01-14T12:04:08.000Z
Make it possible for TableGen to produce code for selecting MOVi32imm.
This allows reasonably recent ARM targets to select a lot more constants
than before.

We achieve this by adding GISelPredicateCode to arm_i32imm. It's
impossible to use the exact same code for both DAGISel and GlobalISel,
since one uses "Subtarget-&gt;" and the other "STI." to refer to the
subtarget. Moreover, in GlobalISel we don't have ready access to the
MachineFunction, so we need to add a bit of code for obtaining it from
the instruction that we're selecting. This is also the reason why it
needs to remain a PatLeaf instead of the more specific IntImmLeaf.

llvm-svn: 351056
diff --git a/llvm/lib/Target/ARM/ARMInstrInfo.td b/llvm/lib/Target/ARM/ARMInstrInfo.td
@@ -722,7 +722,20 @@ def arm_i32imm : PatLeaf<(imm), [{
   if (Subtarget->useMovt(*MF))
     return true;
   return ARM_AM::isSOImmTwoPartVal((unsigned)N->getZExtValue());
-}]>;
+}]> {
+  // Ideally this would be an IntImmLeaf, but then we wouldn't have access to
+  // the MachineFunction.
+  let GISelPredicateCode = [{
+    const auto &MF = *MI.getParent()->getParent();
+    if (STI.useMovt(MF))
+      return true;
+
+    const auto &MO = MI.getOperand(1);
+    if (!MO.isCImm())
+      return false;
+    return ARM_AM::isSOImmTwoPartVal(MO.getCImm()->getZExtValue());
+  }];
+}
 
 /// imm0_1 predicate - Immediate in the range [0,1].
 def Imm0_1AsmOperand: ImmAsmOperand<0,1> { let Name = "Imm0_1"; }
diff --git a/llvm/test/CodeGen/ARM/GlobalISel/arm-instruction-select.mir b/llvm/test/CodeGen/ARM/GlobalISel/arm-instruction-select.mir
@@ -64,8 +64,12 @@
   define void @test_stores() #0 { ret void }
 
   define void @test_gep() { ret void }
+
+  define void @test_MOVi32imm() #3 { ret void }
+
   define void @test_constant_imm() { ret void }
   define void @test_constant_cimm() { ret void }
+
   define void @test_pointer_constant_unconstrained() { ret void }
   define void @test_pointer_constant_constrained() { ret void }
 
@@ -1481,6 +1485,23 @@ body:             |
     BX_RET 14, $noreg, implicit $r0
 ...
 ---
+name:            test_MOVi32imm
+# CHECK-LABEL: name: test_MOVi32imm
+legalized:       true
+regBankSelected: true
+selected:        false
+# CHECK: selected: true
+registers:
+  - { id: 0, class: gprb }
+body:             |
+  bb.0:
+    %0(s32) = G_CONSTANT 65537
+    ; CHECK: %[[C:[0-9]+]]:gpr = MOVi32imm 65537
+
+    $r0 = COPY %0(s32)
+    BX_RET 14, $noreg, implicit $r0
+...
+---
 name:            test_constant_imm
 # CHECK-LABEL: name: test_constant_imm
 legalized:       true
