From 124ac2b997a953ca620d2e339c2b6f6f0fc88abc Mon Sep 17 00:00:00 2001
From: Benjamin Kramer <benny.kra@googlemail.com>
Date: Tue, 26 Jul 2011 22:42:13 +0000
Subject: Add a neat little two's complement hack for x86.

On x86 we can't encode an immediate LHS of a sub directly. If the RHS comes from a XOR with a constant we can
fold the negation into the xor and add one to the immediate of the sub. Then we can turn the sub into an add,
which can be commuted and encoded efficiently.

This code is generated for __builtin_clz and friends.

llvm-svn: 136167
---
 llvm/test/CodeGen/X86/sub.ll | 11 +++++++++++
 1 file changed, 11 insertions(+)
 create mode 100644 llvm/test/CodeGen/X86/sub.ll

(limited to 'llvm/test/CodeGen/X86/sub.ll')

diff --git a/llvm/test/CodeGen/X86/sub.ll b/llvm/test/CodeGen/X86/sub.ll
new file mode 100644
index 00000000000..2a4d2d6e3fc
--- /dev/null
+++ b/llvm/test/CodeGen/X86/sub.ll
@@ -0,0 +1,11 @@
+; RUN: llc -march=x86 < sub.ll | FileCheck %s
+
+define i32 @test1(i32 %x) {
+  %xor = xor i32 %x, 31
+  %sub = sub i32 32, %xor
+  ret i32 %sub
+; CHECK: test1:
+; CHECK:      xorl $-32
+; CHECK-NEXT: addl $33
+; CHECK-NEXT: ret
+}
-- 
cgit v1.2.3