From: Evan Cheng <evan.cheng@apple.com>
Date: Fri, 27 Jan 2006 22:11:01 +0000 (+0000)
Subject: Added notes about a x86 isel deficiency.
X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=e826a018b94c72212021517fb91e6ffb30f1b214;p=oota-llvm.git

Added notes about a x86 isel deficiency.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@25706 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/lib/Target/X86/README.txt b/lib/Target/X86/README.txt
index cb206f3b04e..9410a9acf8d 100644
--- a/lib/Target/X86/README.txt
+++ b/lib/Target/X86/README.txt
@@ -166,3 +166,25 @@ http://gcc.gnu.org/ml/gcc-patches/2004-08/msg02011.html
 
 Combine: a = sin(x), b = cos(x) into a,b = sincos(x).
 
+//===---------------------------------------------------------------------===//
+
+Solve this DAG isel folding deficiency:
+
+int X, Y;
+
+void fn1(void)
+{
+  X = X | (Y << 3);
+}
+
+compiles to
+
+fn1:
+	movl Y, %eax
+	shll $3, %eax
+	orl X, %eax
+	movl %eax, X
+	ret
+
+The problem is the store's chain operand is not the load X but rather
+a TokenFactor of the load X and load Y. This prevents the folding.