Avoid creating duplicate ANDs in SelectionDAG.

[jgalenson]

Summary

When expanding a BRCOND into a BR_CC, do not create an AND 1 if one already exists.

[john.brawn]

test/CodeGen/ARM/wide-compares.ll

39–44

This looks strange - in latest trunk the test is already expecting a bge here. In fact according to svn log wide-compares.ll hasn't changed since the initial commit which already expected bge. Are you sure this patch is for trunk llvm?

[jgalenson]

test/CodeGen/ARM/wide-compares.ll

39–44

Ah, yes, my apologies. This patch is a follow-up to https://reviews.llvm.org/D35821, which has been LGTMed but not yet committed. That patch regresses this test, so we decided to ask whether we wanted to fix it with this patch.

[john.brawn]

LGTM.

lib/CodeGen/SelectionDAG/LegalizeDAG.cpp

case ISD::BRCOND:
     Tmp1 = Node->getOperand(0);
     Tmp2 = Node->getOperand(1);
     if (Tmp2.getOpcode() == ISD::SETCC) {
       Tmp1 = DAG.getNode(ISD::BR_CC, dl, MVT::Other,
                          Tmp1, Tmp2.getOperand(2),
                          Tmp2.getOperand(0), Tmp2.getOperand(1),
                          Node->getOperand(2));
     } else {
-      // We test only the i1 bit.  Skip the AND if UNDEF.
-      Tmp3 = (Tmp2.isUndef()) ? Tmp2 :
-        DAG.getNode(ISD::AND, dl, Tmp2.getValueType(), Tmp2,
+      // We test only the i1 bit.  Skip the AND if UNDEF or another AND.
+      if (Tmp2.isUndef() ||
+          (Tmp2.getOpcode() == ISD::AND &&
+           isa<ConstantSDNode>(Tmp2.getOperand(1)) &&
+           dyn_cast<ConstantSDNode>(Tmp2.getOperand(1))->getZExtValue() == 1))
+        Tmp3 = Tmp2;
+      else
+        Tmp3 = DAG.getNode(ISD::AND, dl, Tmp2.getValueType(), Tmp2,
                            DAG.getConstant(1, dl, Tmp2.getValueType()));
       Tmp1 = DAG.getNode(ISD::BR_CC, dl, MVT::Other, Tmp1,
                          DAG.getCondCode(ISD::SETNE), Tmp3,
                          DAG.getConstant(0, dl, Tmp3.getValueType()),
                          Node->getOperand(2));
     }
     Results.push_back(Tmp1);
     break;
   case ISD::SETCC: {

test/CodeGen/ARM/wide-compares.ll

 ; CHECK-LABEL: test_slt2:
 define void @test_slt2(i64 %a, i64 %b) {
 entry:
   %cmp = icmp slt i64 %a, %b
   ; CHECK-ARM: subs {{[^,]+}}, r0, r2
   ; CHECK-ARM: sbcs {{[^,]+}}, r1, r3
   ; CHECK-THUMB2: subs {{[^,]+}}, r0, r2
   ; CHECK-THUMB2: sbcs.w {{[^,]+}}, r1, r3
-  ; CHECK-ARM: movwge r12, #1
-  ; CHECK-ARM: cmp r12, #0
-  ; CHECK-THUMB2: movge.w r12, #1
-  ; CHECK-THUMB: cmp.w r12, #0
-  ; CHECK: bne [[BB2:\.[0-9A-Za-z_]+]]
+  ; CHECK: bge [[BB2:\.[0-9A-Za-z_]+]]
   br i1 %cmp, label %bb1, label %bb2
 bb1:
   call void @f()
   ret void
 bb2:
   ; CHECK: [[BB2]]:
   ; CHECK-NEXT: bl g
   call void @g()
   ret void
 }
 
 declare void @f()
 declare void @g()