Teach instsimplify some tricks about exact/nuw/nsw shifts.

improve interfaces to instsimplify to take this info.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@125196 91177308-0d34-0410-b5e6-96231b3b80d8

test/Transforms/InstSimplify/exact-nsw-nuw.ll

@@ -0,0 +1,44 @@
+; RUN: opt < %s -instsimplify -S | FileCheck %s
+
+; PR8862
+
+; CHECK: @shift1
+; CHECK: ret i32 %A
+define i32 @shift1(i32 %A, i32 %B) {
+  %C = lshr exact i32 %A, %B
+  %D = shl nuw i32 %C, %B
+  ret i32 %D
+}
+
+; CHECK: @shift2
+; CHECK: lshr
+; CHECK: ret i32 %D
+define i32 @shift2(i32 %A, i32 %B) {
+  %C = lshr i32 %A, %B
+  %D = shl nuw i32 %C, %B
+  ret i32 %D
+}
+
+; CHECK: @shift3
+; CHECK: ret i32 %A
+define i32 @shift3(i32 %A, i32 %B) {
+  %C = ashr exact i32 %A, %B
+  %D = shl nuw i32 %C, %B
+  ret i32 %D
+}
+
+; CHECK: @shift4
+; CHECK: ret i32 %A
+define i32 @shift4(i32 %A, i32 %B) {
+  %C = shl nuw i32 %A, %B
+  %D = lshr i32 %C, %B
+  ret i32 %D
+}
+
+; CHECK: @shift5
+; CHECK: ret i32 %A
+define i32 @shift5(i32 %A, i32 %B) {
+  %C = shl nsw i32 %A, %B
+  %D = ashr i32 %C, %B
+  ret i32 %D
+}