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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@30515 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Target/X86/README.txt b/lib/Target/X86/README.txt
index dd02948f8701c0c66bd04a3836d4ba73d7ce51f9..d2aaa592e6b1f30ab3368a8b160e428a0a8f80d0 100644 (file)
--- a/lib/Target/X86/README.txt
+++ b/lib/Target/X86/README.txt
@@ -734,3 +734,19 @@ This currently compiles to:
        addl $12, %esp
 
 The add\sub pair is really unneeded here.
+
+//===---------------------------------------------------------------------===//
+
+We generate really bad code in some cases due to lowering SETCC/SELECT at 
+legalize time, which prevents the post-legalize dag combine pass from
+understanding the code.  As a silly example, this prevents us from folding 
+stuff like this:
+
+bool %test(ulong %x) {
+  %tmp = setlt ulong %x, 4294967296
+  ret bool %tmp
+}
+
+into x.h == 0
+
+