InstCombine: Check for zero shift amounts before subtracting one causing integer overflow.

PR17026. Also avoid undefined shifts and shift amounts larger than 64 bits
(those are always undef because we can't represent integer types that large).

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@189672 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 36 insertions, 0 deletions

diff --git a/test/Transforms/InstCombine/shift.ll b/test/Transforms/InstCombine/shift.ll
index 0bdab139b7..b1082f06ef 100644
--- a/test/Transforms/InstCombine/shift.ll
+++ b/test/Transforms/InstCombine/shift.ll
@@ -744,3 +744,39 @@ define i32 @test62(i32 %x) {
 ; CHECK-LABEL: @test62(
 ; CHECK: ashr exact i32 %x, 3
 }
+
+; PR17026
+; CHECK-LABEL: @test63(
+; CHECK-NOT: sh
+; CHECK: ret
+define void @test63(i128 %arg) {
+bb:
+  br i1 undef, label %bb1, label %bb12
+
+bb1:                                              ; preds = %bb11, %bb
+  br label %bb2
+
+bb2:                                              ; preds = %bb7, %bb1
+  br i1 undef, label %bb3, label %bb7
+
+bb3:                                              ; preds = %bb2
+  %tmp = lshr i128 %arg, 36893488147419103232
+  %tmp4 = shl i128 %tmp, 0
+  %tmp5 = or i128 %tmp4, undef
+  %tmp6 = trunc i128 %tmp5 to i16
+  br label %bb8
+
+bb7:                                              ; preds = %bb2
+  br i1 undef, label %bb8, label %bb2
+
+bb8:                                              ; preds = %bb7, %bb3
+  %tmp9 = phi i16 [ %tmp6, %bb3 ], [ undef, %bb7 ]
+  %tmp10 = icmp eq i16 %tmp9, 0
+  br i1 %tmp10, label %bb11, label %bb12
+
+bb11:                                             ; preds = %bb8
+  br i1 undef, label %bb1, label %bb12
+
+bb12:                                             ; preds = %bb11, %bb8, %bb
+  ret void
+}