Move some shift transforms out of instcombine and into InstructionSimplify.

While there, I noticed that the transform "undef >>a X -> undef" was wrong.
For example if X is 2 then the top two bits must be equal, so the result can
not be anything.  I fixed this in the constant folder as well.  Also, I made
the transform for "X << undef" stronger: it now folds to undef always, even
though X might be zero.  This is in accordance with the LangRef, but I must
admit that it is fairly aggressive.  Also, I added "i32 X << 32 -> undef"
following the LangRef and the constant folder, likewise fairly aggressive.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@123417 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 16 insertions, 2 deletions

diff --git a/test/Transforms/InstCombine/shift.ll b/test/Transforms/InstCombine/shift.ll
index 4f6939d..3ae74b5 100644
--- a/test/Transforms/InstCombine/shift.ll
+++ b/test/Transforms/InstCombine/shift.ll
@@ -35,18 +35,32 @@ define i32 @test4(i8 %A) {
 
 define i32 @test5(i32 %A) {
 ; CHECK: @test5
-; CHECK: ret i32 0
+; CHECK: ret i32 undef
         %B = lshr i32 %A, 32  ;; shift all bits out 
         ret i32 %B
 }
 
 define i32 @test5a(i32 %A) {
 ; CHECK: @test5a
-; CHECK: ret i32 0
+; CHECK: ret i32 undef
         %B = shl i32 %A, 32     ;; shift all bits out 
         ret i32 %B
 }
 
+define i32 @test5b() {
+; CHECK: @test5b
+; CHECK: ret i32 -1
+        %B = ashr i32 undef, 2  ;; top two bits must be equal, so not undef
+        ret i32 %B
+}
+
+define i32 @test5b2(i32 %A) {
+; CHECK: @test5b2
+; CHECK: ret i32 -1
+        %B = ashr i32 undef, %A  ;; top %A bits must be equal, so not undef
+        ret i32 %B
+}
+
 define i32 @test6(i32 %A) {
 ; CHECK: @test6
 ; CHECK-NEXT: mul i32 %A, 6