Add a note.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@85329 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Target/X86/README.txt b/lib/Target/X86/README.txt
index 046d35c..5967fd5 100644 (file)
--- a/lib/Target/X86/README.txt
+++ b/lib/Target/X86/README.txt
@@ -1952,3 +1952,26 @@ fact these instructions are identical to the non-lock versions. We need a way to
 add target specific information to target nodes and have this information
 carried over to machine instructions. Asm printer (or JIT) can use this
 information to add the "lock" prefix.
+
+//===---------------------------------------------------------------------===//
+
+int func(int a, int b) { if (a & 0x80) b |= 0x80; else b &= 0x80; return b; }
+
+Current:
+
+        movb    %sil, %al
+        andb    $-128, %sil
+        orb     $-128, %al
+        testb   %dil, %dil
+        js      LBB1_2
+        movb    %sil, %al
+LBB1_2:
+        movsbl  %al, %eax
+
+Better:
+        movl    %esi, %eax
+        orl     $-128, %eax
+        andl    $-128, %esi
+        testb   %dil, %dil
+        cmovns  %esi, %eax
+        movsbl  %al,%eax