InstCombine: fold (A << C) == (B << C) --> ((A^B) & (~0U >> C)) == 0

Anding and comparing with zero can be done in a single instruction on
most archs so this is a bit cheaper.

llvm-svn: 233291

1 files changed, 0 insertions, 38 deletions

diff --git a/llvm/lib/Target/README.txt b/llvm/lib/Target/README.txt
index 52a334a6174..282d9234c1a 100644
--- a/llvm/lib/Target/README.txt
+++ b/llvm/lib/Target/README.txt
@@ -1844,44 +1844,6 @@ we remove checking in code like
 
 //===---------------------------------------------------------------------===//
 
-This code (from Benchmarks/Dhrystone/dry.c):
-
-define i32 @Func1(i32, i32) nounwind readnone optsize ssp {
-entry:
-  %sext = shl i32 %0, 24
-  %conv = ashr i32 %sext, 24
-  %sext6 = shl i32 %1, 24
-  %conv4 = ashr i32 %sext6, 24
-  %cmp = icmp eq i32 %conv, %conv4
-  %. = select i1 %cmp, i32 10000, i32 0
-  ret i32 %.
-}
-
-Should be simplified into something like:
-
-define i32 @Func1(i32, i32) nounwind readnone optsize ssp {
-entry:
-  %sext = shl i32 %0, 24
-  %conv = and i32 %sext, 0xFF000000
-  %sext6 = shl i32 %1, 24
-  %conv4 = and i32 %sext6, 0xFF000000
-  %cmp = icmp eq i32 %conv, %conv4
-  %. = select i1 %cmp, i32 10000, i32 0
-  ret i32 %.
-}
-
-and then to:
-
-define i32 @Func1(i32, i32) nounwind readnone optsize ssp {
-entry:
-  %conv = and i32 %0, 0xFF
-  %conv4 = and i32 %1, 0xFF
-  %cmp = icmp eq i32 %conv, %conv4
-  %. = select i1 %cmp, i32 10000, i32 0
-  ret i32 %.
-}
-//===---------------------------------------------------------------------===//
-
 clang -O3 currently compiles this code
 
 int g(unsigned int a) {