Check full block range for loop/continue overlap in RVSDG guards

Selection and switch construct guards now check ALL blocks between
header and merge indices, not just named targets (header, then, else,
merge). Intermediate blocks in the range may be loop continue targets
that must remain reachable.

Author: LegNeato

rust/spirv-tools-opt/src/direct/mod.rs

@@ -625,20 +625,22 @@ pub fn optimize_module_direct(module: &Module) -> Result<Module, EgglogOptError>
     // For each selection construct, convert to RVSDG EffGamma
     for (sel_idx, sel) in selection_constructs.iter().enumerate() {
         // Skip selections that overlap with loop bodies or continue blocks.
-        // Check ALL blocks involved (header, then, else, merge) — not just the header —
-        // because SPIR-V blocks may not be laid out contiguously.
+        // Check ALL blocks in the construct range [header, merge] — not just the
+        // named targets — because intermediate blocks (e.g. continue targets) may
+        // exist between branch targets and the merge block.
         {
             let label_map = &func_block_labels[sel.func_idx];
-            let in_loop = loop_block_set.contains(&(sel.func_idx, sel.header_block_idx))
-                || continue_block_set.contains(&(sel.func_idx, sel.header_block_idx))
-                || [&sel.then_label, &sel.else_label, &sel.merge_label]
-                    .iter()
-                    .any(|label| {
-                        label_map.get(label).map_or(false, |&idx| {
-                            loop_block_set.contains(&(sel.func_idx, idx))
-                                || continue_block_set.contains(&(sel.func_idx, idx))
-                        })
-                    });
+            let merge_idx = label_map.get(&sel.merge_label).copied();
+            let in_loop = if let Some(merge_idx) = merge_idx {
+                // Check all blocks from header to merge (inclusive)
+                (sel.header_block_idx..=merge_idx).any(|idx| {
+                    loop_block_set.contains(&(sel.func_idx, idx))
+                        || continue_block_set.contains(&(sel.func_idx, idx))
+                })
+            } else {
+                // Can't resolve merge — skip to be safe
+                true
+            };
             if in_loop {
                 continue;
             }
@@ -746,21 +748,19 @@ pub fn optimize_module_direct(module: &Module) -> Result<Module, EgglogOptError>
     let mut rvsdg_switches: Vec<RvsdgSwitch> = Vec::new();
 
     for sw in &switch_constructs {
-        // Skip switches that overlap with loop bodies or continue blocks
+        // Skip switches that overlap with loop bodies or continue blocks.
+        // Check ALL blocks in the construct range [header, merge].
         {
             let label_map = &func_block_labels[sw.func_idx];
-            let in_loop = loop_block_set.contains(&(sw.func_idx, sw.header_block_idx))
-                || continue_block_set.contains(&(sw.func_idx, sw.header_block_idx))
-                || sw.case_labels.iter().any(|label| {
-                    label_map.get(label).map_or(false, |&idx| {
-                        loop_block_set.contains(&(sw.func_idx, idx))
-                            || continue_block_set.contains(&(sw.func_idx, idx))
-                    })
-                })
-                || label_map.get(&sw.merge_label).map_or(false, |&idx| {
+            let merge_idx = label_map.get(&sw.merge_label).copied();
+            let in_loop = if let Some(merge_idx) = merge_idx {
+                (sw.header_block_idx..=merge_idx).any(|idx| {
                     loop_block_set.contains(&(sw.func_idx, idx))
                         || continue_block_set.contains(&(sw.func_idx, idx))
-                });
+                })
+            } else {
+                true
+            };
             if in_loop {
                 continue;
             }