DAG: Combine (and (setne X, 0), (setne X, -1)) -> (setuge (add X, 1), 2)

A common idiom is to use zero and all-ones as sentinal values and to
check for both in a single conditional ("x != 0 && x != (unsigned)-1").
That generates code, for i32, like:
  testl %edi, %edi
  setne %al
  cmpl  $-1, %edi
  setne %cl
  andb  %al, %cl

With this transform, we generate the simpler:
  incl  %edi
  cmpl  $1, %edi
  seta  %al

Similar improvements for other integer sizes and on other platforms. In
general, combining the two setcc instructions into one is better.

rdar://14689217

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@188315 91177308-0d34-0410-b5e6-96231b3b80d8

3 files changed, 40 insertions, 0 deletions

diff --git a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 0d71761..0e316db 100644
--- a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -2675,6 +2675,19 @@ SDValue DAGCombiner::visitAND(SDNode *N) {
         return DAG.getSetCC(SDLoc(N), VT, ORNode, LR, Op1);
       }
     }
+    // Simplify (and (setne X, 0), (setne X, -1)) -> (setuge (add X, 1), 2)
+    if (LL == RL && isa<ConstantSDNode>(LR) && isa<ConstantSDNode>(RR) &&
+        Op0 == Op1 && LL.getValueType().isInteger() &&
+      Op0 == ISD::SETNE && ((cast<ConstantSDNode>(LR)->isNullValue() &&
+                                 cast<ConstantSDNode>(RR)->isAllOnesValue()) ||
+                                (cast<ConstantSDNode>(LR)->isAllOnesValue() &&
+                                 cast<ConstantSDNode>(RR)->isNullValue()))) {
+      SDValue ADDNode = DAG.getNode(ISD::ADD, SDLoc(N0), LL.getValueType(),
+                                    LL, DAG.getConstant(1, LL.getValueType()));
+      AddToWorkList(ADDNode.getNode());
+      return DAG.getSetCC(SDLoc(N), VT, ADDNode,
+                          DAG.getConstant(2, LL.getValueType()), ISD::SETUGE);
+    }
     // canonicalize equivalent to ll == rl
     if (LL == RR && LR == RL) {
       Op1 = ISD::getSetCCSwappedOperands(Op1);
diff --git a/test/CodeGen/ARM/setcc-sentinals.ll b/test/CodeGen/ARM/setcc-sentinals.ll
new file mode 100644
index 0000000..4033a81
--- /dev/null
+++ b/test/CodeGen/ARM/setcc-sentinals.ll
@@ -0,0 +1,14 @@
+; RUN: llc < %s -mcpu=cortex-a8 -march=arm -asm-verbose=false | FileCheck %s
+
+define zeroext i1 @test0(i32 %x) nounwind {
+; CHECK-LABEL: test0:
+; CHECK-NEXT: add [[REG:(r[0-9]+)|(lr)]], r0, #1
+; CHECK-NEXT: mov r0, #0
+; CHECK-NEXT: cmp [[REG]], #1
+; CHECK-NEXT: movhi r0, #1
+; CHECK-NEXT: bx  lr
+  %cmp1 = icmp ne i32 %x, -1
+  %not.cmp = icmp ne i32 %x, 0
+  %.cmp1 = and i1 %cmp1, %not.cmp
+  ret i1 %.cmp1
+}
diff --git a/test/CodeGen/X86/setcc-sentinals.ll b/test/CodeGen/X86/setcc-sentinals.ll
new file mode 100644
index 0000000..cae5f58
--- /dev/null
+++ b/test/CodeGen/X86/setcc-sentinals.ll
@@ -0,0 +1,13 @@
+; RUN: llc < %s -mcpu=generic -march=x86-64 -asm-verbose=false | FileCheck %s
+
+define zeroext i1 @test0(i64 %x) nounwind {
+; CHECK-LABEL: test0:
+; CHECK-NEXT: incq %rdi
+; CHECK-NEXT: cmpq $1, %rdi
+; CHECK-NEXT: seta %al
+; CHECK-NEXT: ret
+  %cmp1 = icmp ne i64 %x, -1
+  %not.cmp = icmp ne i64 %x, 0
+  %.cmp1 = and i1 %cmp1, %not.cmp
+  ret i1 %.cmp1
+}