New instcombine rule: max(~a,~b) -> ~min(a, b)

This case is interesting because ScalarEvolutionExpander lowers min(a,
b) as ~max(~a,~b).  I think the profitability heuristics can be made
more clever/aggressive, but this is a start.

Differential Revision: http://reviews.llvm.org/D7821

llvm-svn: 230285

1 files changed, 68 insertions, 0 deletions

diff --git a/llvm/test/Transforms/InstCombine/max-of-nots.ll b/llvm/test/Transforms/InstCombine/max-of-nots.ll
new file mode 100644
index 00000000000..41e3038cbe2
--- /dev/null
+++ b/llvm/test/Transforms/InstCombine/max-of-nots.ll
@@ -0,0 +1,68 @@
+; RUN: opt -S -instcombine < %s | FileCheck %s
+
+define i32 @compute_min_2(i32 %x, i32 %y) {
+; CHECK-LABEL: compute_min_2
+ entry:
+  %not_x = sub i32 -1, %x
+  %not_y = sub i32 -1, %y
+  %cmp = icmp sgt i32 %not_x, %not_y
+  %not_min = select i1 %cmp, i32 %not_x, i32 %not_y
+  %min = sub i32 -1, %not_min
+  ret i32 %min
+
+; CHECK: %0 = icmp slt i32 %x, %y
+; CHECK-NEXT: %1 = select i1 %0, i32 %x, i32 %y
+; CHECK-NEXT: ret i32 %1
+}
+
+define i32 @compute_min_3(i32 %x, i32 %y, i32 %z) {
+; CHECK-LABEL: compute_min_3
+ entry:
+  %not_x = sub i32 -1, %x
+  %not_y = sub i32 -1, %y
+  %not_z = sub i32 -1, %z
+  %cmp_1 = icmp sgt i32 %not_x, %not_y
+  %not_min_1 = select i1 %cmp_1, i32 %not_x, i32 %not_y
+  %cmp_2 = icmp sgt i32 %not_min_1, %not_z
+  %not_min_2 = select i1 %cmp_2, i32 %not_min_1, i32 %not_z
+  %min = sub i32 -1, %not_min_2
+  ret i32 %min
+
+; CHECK: %0 = icmp slt i32 %x, %y
+; CHECK-NEXT: %1 = select i1 %0, i32 %x, i32 %y
+; CHECK-NEXT: %2 = icmp slt i32 %1, %z
+; CHECK-NEXT: %3 = select i1 %2, i32 %1, i32 %z
+; CHECK-NEXT: ret i32 %3
+}
+
+define i32 @compute_min_arithmetic(i32 %x, i32 %y) {
+; CHECK-LABEL: compute_min_arithmetic
+ entry:
+  %not_value = sub i32 3, %x
+  %not_y = sub i32 -1, %y
+  %cmp = icmp sgt i32 %not_value, %not_y
+  %not_min = select i1 %cmp, i32 %not_value, i32 %not_y
+  ret i32 %not_min
+
+; CHECK: %0 = add i32 %x, -4
+; CHECK-NEXT: %1 = icmp slt i32 %0, %y
+; CHECK-NEXT: %2 = select i1 %1, i32 %0, i32 %y
+; CHECK-NEXT: %3 = xor i32 %2, -1
+; CHECK-NEXT: ret i32 %3
+}
+
+declare void @fake_use(i32)
+
+define i32 @compute_min_pessimization(i32 %x, i32 %y) {
+; CHECK-LABEL: compute_min_pessimization
+ entry:
+  %not_value = sub i32 3, %x
+  call void @fake_use(i32 %not_value)
+  %not_y = sub i32 -1, %y
+  %cmp = icmp sgt i32 %not_value, %not_y
+; CHECK: %not_value = sub i32 3, %x
+; CHECK: %cmp = icmp sgt i32 %not_value, %not_y
+  %not_min = select i1 %cmp, i32 %not_value, i32 %not_y
+  %min = sub i32 -1, %not_min
+  ret i32 %min
+}