From 072f83c68257ec36ef3113b21eb765ce9f519da7 Mon Sep 17 00:00:00 2001
From: James Price <jrprice@google.com>
Date: Thu, 2 Feb 2023 00:29:27 +0000
Subject: [PATCH] tint/uniformity: filter should not affect result

A derivative_uniformity diagnostic filter should not affect the
uniformity of the return value of a derivative builtin.

Fixed: tint:1815
Change-Id: I58e714978dab747598af5136dc9808a5a658c60e
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/118001
Commit-Queue: James Price <jrprice@google.com>
Reviewed-by: David Neto <dneto@google.com>
Kokoro: Kokoro <noreply+kokoro@google.com>
---
 src/tint/resolver/uniformity.cc      |  2 +-
 src/tint/resolver/uniformity_test.cc | 34 ++++++++++++++++++++++++++++
 2 files changed, 35 insertions(+), 1 deletion(-)

diff --git a/src/tint/resolver/uniformity.cc b/src/tint/resolver/uniformity.cc
index ec10d92398..6c4b53a5ee 100644
--- a/src/tint/resolver/uniformity.cc
+++ b/src/tint/resolver/uniformity.cc
@@ -1512,8 +1512,8 @@ class UniformityGraph {
                         sem_.DiagnosticSeverity(call, ast::DiagnosticRule::kDerivativeUniformity);
                     if (severity != ast::DiagnosticSeverity::kOff) {
                         callsite_tag = {CallSiteTag::CallSiteRequiredToBeUniform, severity};
-                        function_tag = ReturnValueMayBeNonUniform;
                     }
+                    function_tag = ReturnValueMayBeNonUniform;
                 } else if (builtin->IsAtomic()) {
                     callsite_tag = {CallSiteTag::CallSiteNoRestriction};
                     function_tag = ReturnValueMayBeNonUniform;
diff --git a/src/tint/resolver/uniformity_test.cc b/src/tint/resolver/uniformity_test.cc
index 59e42df4f1..334352de4f 100644
--- a/src/tint/resolver/uniformity_test.cc
+++ b/src/tint/resolver/uniformity_test.cc
@@ -8132,6 +8132,40 @@ test:35:7 note: reading from read_write storage buffer 'non_uniform' may result
 )");
 }
 
+TEST_F(UniformityAnalysisDiagnosticFilterTest, BuiltinReturnValueNotAffected) {
+    // Make sure that a diagnostic filter does not affect the uniformity of the return value of a
+    // derivative builtin.
+    std::string src = R"(
+fn foo() {
+  var x: f32;
+
+  @diagnostic(off,derivative_uniformity) {
+    x = dpdx(1.0);
+  }
+
+  if (x < 0.5) {
+    _ = dpdy(1.0); // Should trigger an error
+  }
+}
+
+)";
+
+    RunTest(src, false);
+    EXPECT_EQ(error_,
+              R"(test:10:9 error: 'dpdy' must only be called from uniform control flow
+    _ = dpdy(1.0); // Should trigger an error
+        ^^^^
+
+test:9:3 note: control flow depends on possibly non-uniform value
+  if (x < 0.5) {
+  ^^
+
+test:6:9 note: return value of 'dpdx' may be non-uniform
+    x = dpdx(1.0);
+        ^^^^
+)");
+}
+
 TEST_F(UniformityAnalysisDiagnosticFilterTest, BarriersNotAffected) {
     // Make sure that the diagnostic filter does not affect barriers.
     std::string src = R"(