Factor the (x & 2^n) ? 2^m : 0 instcombine into its own method and generalize it

[oota-llvm.git] / lib / Target / X86 / README.txt

diff --git a/lib/Target/X86/README.txt b/lib/Target/X86/README.txt
index a305ae6ec5505eea1d01814a6ae8b49f7c8734d6..181c1bd4a9a1325e94f0dd9558dad7f33d7fea26 100644 (file)
--- a/lib/Target/X86/README.txt
+++ b/lib/Target/X86/README.txt
@@ -1736,46 +1736,6 @@ Ideal output:
 
 //===---------------------------------------------------------------------===//
 
-Testcase:
-int x(int a) { return (a & 0x80) ? 0x100 : 0; }
-int y(int a) { return (a & 0x80) *2; }
-
-Current:
-       testl   $128, 4(%esp)
-       setne   %al
-       movzbl  %al, %eax
-       shll    $8, %eax
-       ret
-
-Better:
-       movl    4(%esp), %eax
-       addl    %eax, %eax
-       andl    $256, %eax
-       ret
-
-This is another general instcombine transformation that is profitable on all
-targets.  In LLVM IR, these functions look like this:
-
-define i32 @x(i32 %a) nounwind readnone {
-entry:
-       %0 = and i32 %a, 128
-       %1 = icmp eq i32 %0, 0
-       %iftmp.0.0 = select i1 %1, i32 0, i32 256
-       ret i32 %iftmp.0.0
-}
-
-define i32 @y(i32 %a) nounwind readnone {
-entry:
-       %0 = shl i32 %a, 1
-       %1 = and i32 %0, 256
-       ret i32 %1
-}
-
-Replacing an icmp+select with a shift should always be considered profitable in
-instcombine.
-
-//===---------------------------------------------------------------------===//
-
 Re-implement atomic builtins __sync_add_and_fetch() and __sync_sub_and_fetch
 properly.