[InstCombine] Add new rule for MIN(MAX(~A, ~B), ~C) et. al.

Summary:
Optimizing these well are especially interesting for IRCE since it
"clamps" values by generating this sort of pattern through SCEV
expressions.

Depends on D9352.

Reviewers: majnemer

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D9353

llvm-svn: 236203

1 files changed, 17 insertions, 0 deletions

diff --git a/llvm/test/Transforms/InstCombine/max-of-nots.ll b/llvm/test/Transforms/InstCombine/max-of-nots.ll
index 41e3038cbe2..dd9c54b0673 100644
--- a/llvm/test/Transforms/InstCombine/max-of-nots.ll
+++ b/llvm/test/Transforms/InstCombine/max-of-nots.ll
@@ -66,3 +66,20 @@ define i32 @compute_min_pessimization(i32 %x, i32 %y) {
   %min = sub i32 -1, %not_min
   ret i32 %min
 }
+
+define i32 @max_of_nots(i32 %x, i32 %y) {
+; CHECK-LABEL: @max_of_nots(
+; CHECK-NEXT: icmp
+; CHECK-NEXT: select
+; CHECK-NEXT: icmp
+; CHECK-NEXT: select
+; CHECK-NEXT: xor
+; CHECK-NEXT: ret
+  %c0 = icmp sgt i32 %y, 0
+  %xor_y = xor i32 %y, -1
+  %s0 = select i1 %c0, i32 %xor_y, i32 -1
+  %xor_x = xor i32 %x, -1
+  %c1 = icmp slt i32 %s0, %xor_x
+  %smax96 = select i1 %c1, i32 %xor_x, i32 %s0
+  ret i32 %smax96
+}