Another micro-opt.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@42554 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Target/X86/README.txt b/lib/Target/X86/README.txt
index 81e9797f05facc4c43bcf3f88c2974b8f2b0fb22..0fd79f236111860da995d6b08df55570869bc5fe 100644 (file)
--- a/lib/Target/X86/README.txt
+++ b/lib/Target/X86/README.txt
@@ -1306,3 +1306,19 @@ However, ICC caches this information before the loop and produces this:
         movl      88(%esp), %eax                                #481.12
 
 //===---------------------------------------------------------------------===//
+
+This code:
+
+       %tmp659 = icmp slt i16 %tmp654, 0               ; <i1> [#uses=1]
+       br i1 %tmp659, label %cond_true662, label %cond_next715
+
+produces this:
+
+       testw   %cx, %cx
+       movswl  %cx, %esi
+       jns     LBB4_109        # cond_next715
+
+Shark tells us that using %cx in the testw instruction is sub-optimal. It
+suggests using the 32-bit register (which is what ICC uses).
+
+//===---------------------------------------------------------------------===//