Fold (add x, shl(0 - y, n)) -> sub(x, shl(y, n)), to simplify some code

that SCEVExpander can produce when running on behalf of LSR.

llvm-svn: 93949

1 files changed, 17 insertions, 0 deletions

diff --git a/llvm/test/CodeGen/X86/neg-shl-add.ll b/llvm/test/CodeGen/X86/neg-shl-add.ll
new file mode 100644
index 00000000000..7aebc383dde
--- /dev/null
+++ b/llvm/test/CodeGen/X86/neg-shl-add.ll
@@ -0,0 +1,17 @@
+; RUN: llc -march=x86-64 < %s | not grep negq
+
+; These sequences don't need neg instructions; they can be done with
+; a single shift and sub each.
+
+define i64 @foo(i64 %x, i64 %y, i64 %n) nounwind {
+  %a = sub i64 0, %y
+  %b = shl i64 %a, %n
+  %c = add i64 %b, %x
+  ret i64 %c
+}
+define i64 @boo(i64 %x, i64 %y, i64 %n) nounwind {
+  %a = sub i64 0, %y
+  %b = shl i64 %a, %n
+  %c = add i64 %x, %b
+  ret i64 %c
+}