[Test] Opportunity for sinking to unreachable in InstCombine

Author: xortator

llvm/test/Transforms/InstCombine/sink_to_unreachable.ll

@@ -0,0 +1,72 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt -instcombine -S < %s | FileCheck %s
+; RUN: opt -passes=instcombine -S < %s | FileCheck %s
+
+declare void @use(i32 %x)
+
+define void @test_01(i32 %x, i32 %y) {
+; CHECK-LABEL: @test_01(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[C2:%.*]] = icmp slt i32 [[X:%.*]], [[Y:%.*]]
+; CHECK-NEXT:    br i1 [[C2]], label [[EXIT:%.*]], label [[UNREACHED:%.*]]
+; CHECK:       unreached:
+; CHECK-NEXT:    [[C1:%.*]] = icmp ne i32 [[X]], [[Y]]
+; CHECK-NEXT:    [[COMPARATOR:%.*]] = zext i1 [[C1]] to i32
+; CHECK-NEXT:    call void @use(i32 [[COMPARATOR]])
+; CHECK-NEXT:    unreachable
+; CHECK:       exit:
+; CHECK-NEXT:    ret void
+;
+entry:
+  %c1 = icmp eq i32 %x, %y
+  %c2 = icmp slt i32 %x, %y
+  %signed = select i1 %c2, i32 -1, i32 1
+  %comparator = select i1 %c1, i32 0, i32 %signed
+  br i1 %c2, label %exit, label %unreached
+
+unreached:
+  call void @use(i32 %comparator)
+  unreachable
+
+exit:
+  ret void
+}
+
+
+; TODO: %comparator and %signed can be sunk down to unreachable just as in
+; test above.
+define void @test_02(i32 %x, i32 %y) {
+; CHECK-LABEL: @test_02(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[C1:%.*]] = icmp eq i32 [[X:%.*]], [[Y:%.*]]
+; CHECK-NEXT:    [[C2:%.*]] = icmp slt i32 [[X]], [[Y]]
+; CHECK-NEXT:    [[SIGNED:%.*]] = select i1 [[C2]], i32 -1, i32 1
+; CHECK-NEXT:    [[COMPARATOR:%.*]] = select i1 [[C1]], i32 0, i32 [[SIGNED]]
+; CHECK-NEXT:    br i1 [[C2]], label [[EXIT:%.*]], label [[MEDIUM:%.*]]
+; CHECK:       medium:
+; CHECK-NEXT:    [[C3:%.*]] = icmp sgt i32 [[X]], [[Y]]
+; CHECK-NEXT:    br i1 [[C3]], label [[EXIT]], label [[UNREACHED:%.*]]
+; CHECK:       unreached:
+; CHECK-NEXT:    call void @use(i32 [[COMPARATOR]])
+; CHECK-NEXT:    unreachable
+; CHECK:       exit:
+; CHECK-NEXT:    ret void
+;
+entry:
+  %c1 = icmp eq i32 %x, %y
+  %c2 = icmp slt i32 %x, %y
+  %signed = select i1 %c2, i32 -1, i32 1
+  %comparator = select i1 %c1, i32 0, i32 %signed
+  br i1 %c2, label %exit, label %medium
+
+medium:
+  %c3 = icmp sgt i32 %x, %y
+  br i1 %c3, label %exit, label %unreached
+
+unreached:
+  call void @use(i32 %comparator)
+  unreachable
+
+exit:
+  ret void
+}