[X86] Emit more efficient >= comparisons against 0

We don't do a great job with >= 0 comparisons against zero when the
result is used as an i8.

Given something like:
  void f(long long LL, bool *B) {
    *B = LL >= 0;
  }

We used to generate:
  shrq    $63, %rdi
  xorb    $1, %dil
  movb    %dil, (%rsi)

Now we generate:
  testq   %rdi, %rdi
  setns   (%rsi)

Differential Revision: http://reviews.llvm.org/D12136

llvm-svn: 245498

1 files changed, 44 insertions, 0 deletions

diff --git a/llvm/test/CodeGen/X86/cmp.ll b/llvm/test/CodeGen/X86/cmp.ll
index 584179aacbc..eb9a2901142 100644
--- a/llvm/test/CodeGen/X86/cmp.ll
+++ b/llvm/test/CodeGen/X86/cmp.ll
@@ -211,3 +211,47 @@ define zeroext i1 @test15(i32 %bf.load, i32 %n) {
 ; CHECK:  shrl	$16, %edi
 ; CHECK:  cmpl	%esi, %edi
 }
+
+define i8 @test16(i16 signext %L) {
+  %lshr  = lshr i16 %L, 15
+  %trunc = trunc i16 %lshr to i8
+  %not   = xor i8 %trunc, 1
+  ret i8 %not
+
+; CHECK-LABEL: test16:
+; CHECK:  testw   %di, %di
+; CHECK:  setns   %al
+}
+
+define i8 @test17(i32 %L) {
+  %lshr  = lshr i32 %L, 31
+  %trunc = trunc i32 %lshr to i8
+  %not   = xor i8 %trunc, 1
+  ret i8 %not
+
+; CHECK-LABEL: test17:
+; CHECK:  testl   %edi, %edi
+; CHECK:  setns   %al
+}
+
+define i8 @test18(i64 %L) {
+  %lshr  = lshr i64 %L, 63
+  %trunc = trunc i64 %lshr to i8
+  %not   = xor i8 %trunc, 1
+  ret i8 %not
+
+; CHECK-LABEL: test18:
+; CHECK:  testq   %rdi, %rdi
+; CHECK:  setns   %al
+}
+
+define zeroext i1 @test19(i32 %L) {
+  %lshr  = lshr i32 %L, 31
+  %trunc = trunc i32 %lshr to i1
+  %not   = xor i1 %trunc, 1
+  ret i1 %not
+
+; CHECK-LABEL: test19:
+; CHECK:  testl   %edi, %edi
+; CHECK:  setns   %al
+}