[dev.ssa] cmd/compile: rewrite user nil check as OpIsNonNil

Rewite user nil checks as OpIsNonNil so our nil check elimination pass
can take advantage and remove redundant checks.

With make.bash this removes 10% more nilchecks (34110 vs 31088).

Change-Id: Ifb01d1b6d2d759f5e2a5aaa0470e1d5a2a680212
Reviewed-on: https://go-review.googlesource.com/14321
Reviewed-by: Keith Randall <khr@golang.org>
Reviewed-by: Josh Bleecher Snyder <josharian@gmail.com>

1 files changed, 40 insertions, 0 deletions

diff --git a/src/cmd/compile/internal/ssa/nilcheck_test.go b/src/cmd/compile/internal/ssa/nilcheck_test.go
index c54f86a7b4..1d048fbb34 100644
--- a/src/cmd/compile/internal/ssa/nilcheck_test.go
+++ b/src/cmd/compile/internal/ssa/nilcheck_test.go
@@ -342,3 +342,43 @@ func TestNilcheckInFalseBranch(t *testing.T) {
 		t.Errorf("removed thirdCheck, but shouldn't have [false branch]")
 	}
 }
+
+// TestNilcheckUser verifies that a user nil check that dominates a generated nil check
+// wil remove the generated nil check.
+func TestNilcheckUser(t *testing.T) {
+	ptrType := &TypeImpl{Size_: 8, Ptr: true, Name: "testptr"} // dummy for testing
+	c := NewConfig("amd64", DummyFrontend{t})
+	fun := Fun(c, "entry",
+		Bloc("entry",
+			Valu("mem", OpArg, TypeMem, 0, ".mem"),
+			Valu("sb", OpSB, TypeInvalid, 0, nil),
+			Goto("checkPtr")),
+		Bloc("checkPtr",
+			Valu("ptr1", OpConstPtr, ptrType, 0, nil, "sb"),
+			Valu("nilptr", OpConstNil, ptrType, 0, nil, "sb"),
+			Valu("bool1", OpNeqPtr, TypeBool, 0, nil, "ptr1", "nilptr"),
+			If("bool1", "secondCheck", "exit")),
+		Bloc("secondCheck",
+			Valu("bool2", OpIsNonNil, TypeBool, 0, nil, "ptr1"),
+			If("bool2", "extra", "exit")),
+		Bloc("extra",
+			Goto("exit")),
+		Bloc("exit",
+			Exit("mem")))
+
+	CheckFunc(fun.f)
+	// we need the opt here to rewrite the user nilcheck
+	opt(fun.f)
+	nilcheckelim(fun.f)
+
+	// clean up the removed nil check
+	fuse(fun.f)
+	deadcode(fun.f)
+
+	CheckFunc(fun.f)
+	for _, b := range fun.f.Blocks {
+		if b == fun.blocks["secondCheck"] && isNilCheck(b) {
+			t.Errorf("secondCheck was not eliminated")
+		}
+	}
+}