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

1 files changed, 16 insertions, 0 deletions

diff --git a/lib/Target/X86/README.txt b/lib/Target/X86/README.txt
index dd02948f87..d2aaa592e6 100644
--- 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
+
+