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

llvm-svn: 188315

2 files changed, 27 insertions, 0 deletions

diff --git a/llvm/test/CodeGen/ARM/setcc-sentinals.ll b/llvm/test/CodeGen/ARM/setcc-sentinals.ll
new file mode 100644
index 00000000000..4033a810985
--- /dev/null
+++ b/llvm/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/llvm/test/CodeGen/X86/setcc-sentinals.ll b/llvm/test/CodeGen/X86/setcc-sentinals.ll
new file mode 100644
index 00000000000..cae5f58d17f
--- /dev/null
+++ b/llvm/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
+}