[RISCV] Precommit test case to show bug in RISCVISelDagToDag

[eopXD]

Summary

The optimization level should not be restored into O2.
This is a pre-commit test case to show fix in D126641.

[craig.topper]

LGTM

llvm/test/CodeGen/RISCV/isel-optnone.ll

+; REQUIRES: asserts
+; RUN: llc < %s -O0 -mtriple=riscv64 -debug-only=isel 2>&1 | FileCheck %s
+
+define i32* @fooOptnone(i32* %p, i32* %q, i32** %z) #0 {
+; CHECK: Changing optimization level for Function fooOptnone
+; CHECL: Before: -O2 ; After: -O0
+
+; CHECK: Restoring optimization level for Function fooOptnone
+; CHECK: Before: -O0 ; After: -O2
+entry:
+  %r = load i32, i32* %p
+  %s = load i32, i32* %q
+  %y = load i32*, i32** %z
+
+  %t0 = add i32 %r, %s
+  %t1 = add i32 %t0, 1
+  %t2 = getelementptr i32, i32* %y, i32 1
+  %t3 = getelementptr i32, i32* %t2, i32 %t1
+
+  ret i32* %t3
+
+}
+
+attributes #0 = { nounwind optnone noinline }