InstCombine: Fold away tautological masked compares

It is impossible for (x & INT_MAX) == 0 && x == INT_MAX to ever be true.

While this sort of reasoning should normally live in InstSimplify,
the machinery that derives this result is not trivial to split out.

llvm-svn: 222230

1 files changed, 20 insertions, 0 deletions

diff --git a/llvm/test/Transforms/InstCombine/icmp-logical.ll b/llvm/test/Transforms/InstCombine/icmp-logical.ll
index d5d8cbc8c26..faae2016e20 100644
--- a/llvm/test/Transforms/InstCombine/icmp-logical.ll
+++ b/llvm/test/Transforms/InstCombine/icmp-logical.ll
@@ -150,3 +150,23 @@ define i1 @nomask_rhs(i32 %in) {
   %val = or i1 %tst1, %tst2
   ret i1 %val
 }
+
+define i1 @fold_mask_cmps_to_false(i32 %x) {
+; CHECK-LABEL: @fold_mask_cmps_to_false
+; CHECK: ret i1 false
+  %1 = and i32 %x, 2147483647
+  %2 = icmp eq i32 %1, 0
+  %3 = icmp eq i32 %x, 2147483647
+  %4 = and i1 %3, %2
+  ret i1 %4
+}
+
+define i1 @fold_mask_cmps_to_true(i32 %x) {
+; CHECK-LABEL: @fold_mask_cmps_to_true
+; CHECK: ret i1 true
+  %1 = and i32 %x, 2147483647
+  %2 = icmp ne i32 %1, 0
+  %3 = icmp ne i32 %x, 2147483647
+  %4 = or i1 %3, %2
+  ret i1 %4
+}