Fix a README item by having InstructionSimplify do a mild form of value

numbering, in which it considers (for example) "%a = add i32 %x, %y" and
"%b = add i32 %x, %y" to be equal because the operands are equal and the
result of the instructions only depends on the values of the operands.
This has almost no effect (it removes 4 instructions from gcc-as-one-file),
and perhaps slows down compilation: I measured a 0.4% slowdown on the large
gcc-as-one-file testcase, but it wasn't statistically significant.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@122654 91177308-0d34-0410-b5e6-96231b3b80d8

test/Transforms/InstSimplify/2010-12-31-ValueNumber.ll

@@ -0,0 +1,9 @@
+; RUN: opt < %s -instsimplify -S | FileCheck %s
+define i1 @g(i32 %a) nounwind readnone {
+; CHECK: @g
+  %add = shl i32 %a, 1
+  %mul = shl i32 %a, 1
+  %cmp = icmp ugt i32 %add, %mul
+  ret i1 %cmp
+; CHECK: ret i1 false
+}