New entry.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@43420 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Target/X86/README.txt b/lib/Target/X86/README.txt
index 41b38d84c8aa3c7aa9b6ae2fe0ff27e16f518c0e..567d5c4ebbd259d6a0899d6c8bc18ac3adb2609d 100644 (file)
--- a/lib/Target/X86/README.txt
+++ b/lib/Target/X86/README.txt
@@ -1429,3 +1429,65 @@ Possible optimizations:
 +    }
 +  }
 //===---------------------------------------------------------------------===//
+
+main ()
+{
+  int i = 0;
+  unsigned long int z = 0;
+
+  do {
+    z -= 0x00004000;
+    i++;
+    if (i > 0x00040000)
+      abort ();
+  } while (z > 0);
+  exit (0);
+}
+
+gcc compiles this to:
+
+_main:
+       subl    $28, %esp
+       xorl    %eax, %eax
+       jmp     L2
+L3:
+       cmpl    $262144, %eax
+       je      L10
+L2:
+       addl    $1, %eax
+       cmpl    $262145, %eax
+       jne     L3
+       call    L_abort$stub
+L10:
+       movl    $0, (%esp)
+       call    L_exit$stub
+
+llvm:
+
+_main:
+       subl    $12, %esp
+       movl    $1, %eax
+       movl    $16384, %ecx
+LBB1_1:        # bb
+       cmpl    $262145, %eax
+       jge     LBB1_4  # cond_true
+LBB1_2:        # cond_next
+       incl    %eax
+       addl    $4294950912, %ecx
+       cmpl    $16384, %ecx
+       jne     LBB1_1  # bb
+LBB1_3:        # bb11
+       xorl    %eax, %eax
+       addl    $12, %esp
+       ret
+LBB1_4:        # cond_true
+       call    L_abort$stub
+
+1. LSR should rewrite the first cmp with induction variable %ecx.
+2. DAG combiner should fold
+        leal    1(%eax), %edx
+        cmpl    $262145, %edx
+   =>
+        cmpl    $262144, %eax
+
+//===---------------------------------------------------------------------===//