From 27e4ba59e4918494fca1e4cc2222a2dfdaa4a888 Mon Sep 17 00:00:00 2001
From: Dzmitry Malyshau <dmalyshau@mozilla.com>
Date: Fri, 13 Aug 2021 00:37:02 -0400
Subject: [PATCH] Validate that SampleLevel::Exact isn't used for comparisons

---
 src/back/msl/writer.rs             | 2 +-
 src/front/spv/image.rs             | 7 ++++++-
 src/valid/expression.rs            | 6 ++++++
 tests/out/analysis/shadow.info.ron | 2 +-
 tests/out/ir/shadow.ron            | 2 +-
 5 files changed, 15 insertions(+), 4 deletions(-)

diff --git a/src/back/msl/writer.rs b/src/back/msl/writer.rs
index 465992d82a..f206973b1e 100644
--- a/src/back/msl/writer.rs
+++ b/src/back/msl/writer.rs
@@ -2625,7 +2625,7 @@ fn test_stack_size() {
         let stack_size = addresses.end - addresses.start;
         // check the size (in debug only)
         // last observed macOS value: 17504
-        if stack_size < 14000 || stack_size > 19000 {
+        if stack_size < 13000 || stack_size > 19000 {
             panic!("`put_block` stack size {} has changed!", stack_size);
         }
     }
diff --git a/src/front/spv/image.rs b/src/front/spv/image.rs
index 72c10c1231..fac750ddb9 100644
--- a/src/front/spv/image.rs
+++ b/src/front/spv/image.rs
@@ -449,7 +449,12 @@ impl<I: Iterator<Item = u32>> super::Parser<I> {
                 spirv::ImageOperands::LOD => {
                     let lod_expr = self.next()?;
                     let lod_handle = self.lookup_expression.lookup(lod_expr)?.handle;
-                    level = crate::SampleLevel::Exact(lod_handle);
+                    level = if options.compare {
+                        log::debug!("Assuming {:?} is zero", lod_handle);
+                        crate::SampleLevel::Zero
+                    } else {
+                        crate::SampleLevel::Exact(lod_handle)
+                    };
                     words_left -= 1;
                 }
                 spirv::ImageOperands::GRAD => {
diff --git a/src/valid/expression.rs b/src/valid/expression.rs
index 73cc0d1322..2324fb5184 100644
--- a/src/valid/expression.rs
+++ b/src/valid/expression.rs
@@ -93,6 +93,8 @@ pub enum ExpressionError {
     InvalidSampleOffset(crate::ImageDimension, Handle<crate::Constant>),
     #[error("Depth reference {0:?} is not a scalar float")]
     InvalidDepthReference(Handle<crate::Expression>),
+    #[error("Depth sample level can only be Auto or Zero")]
+    InvalidDepthSampleLevel,
     #[error("Sample level (exact) type {0:?} is not a scalar float")]
     InvalidSampleLevelExactType(Handle<crate::Expression>),
     #[error("Sample level (bias) type {0:?} is not a scalar float")]
@@ -451,6 +453,10 @@ impl super::Validator {
                         } => {}
                         _ => return Err(ExpressionError::InvalidDepthReference(expr)),
                     }
+                    match level {
+                        crate::SampleLevel::Auto | crate::SampleLevel::Zero => {}
+                        _ => return Err(ExpressionError::InvalidDepthSampleLevel),
+                    }
                 }
 
                 // check level properties
diff --git a/tests/out/analysis/shadow.info.ron b/tests/out/analysis/shadow.info.ron
index 142cdb0781..f5695163b2 100644
--- a/tests/out/analysis/shadow.info.ron
+++ b/tests/out/analysis/shadow.info.ron
@@ -385,7 +385,7 @@
                             bits: 0,
                         ),
                     ),
-                    ref_count: 1,
+                    ref_count: 0,
                     assignable_global: None,
                     ty: Value(Scalar(
                         kind: Float,
diff --git a/tests/out/ir/shadow.ron b/tests/out/ir/shadow.ron
index 52fa481c86..c71064af86 100644
--- a/tests/out/ir/shadow.ron
+++ b/tests/out/ir/shadow.ron
@@ -1039,7 +1039,7 @@
                     coordinate: 72,
                     array_index: Some(74),
                     offset: None,
-                    level: Exact(25),
+                    level: Zero,
                     depth_ref: Some(69),
                 ),
             ],