From 9b97ddf29a10ec9c73d5e2afe5013eaff9e4b5ba Mon Sep 17 00:00:00 2001
From: Sean Stangl <sean.stangl@gmail.com>
Date: Thu, 18 Jul 2019 09:59:28 -0600
Subject: [PATCH] Enable basic block checks through a feature. (#856)

This allows prefixing BB-specific code with "#[cfg(feature = "basic-blocks")]",
which avoids having to reference an environment variable across the codebase.

The easiest way to enable the feature locally is to add the arguments
'features = ["basic-blocks"]' to the workspace Cargo.toml, where it defines
the cranelift-codegen dependency.
---
 cranelift/codegen/Cargo.toml          |  3 +++
 cranelift/codegen/src/verifier/mod.rs | 11 +++--------
 2 files changed, 6 insertions(+), 8 deletions(-)

diff --git a/cranelift/codegen/Cargo.toml b/cranelift/codegen/Cargo.toml
index aa579c4cde..a9834dac07 100644
--- a/cranelift/codegen/Cargo.toml
+++ b/cranelift/codegen/Cargo.toml
@@ -62,6 +62,9 @@ riscv = []
 # For dependent crates that want to serialize some parts of cranelift
 enable-serde = ["serde"]
 
+# Temporary feature that enforces basic block semantics.
+basic-blocks = []
+
 [badges]
 maintenance = { status = "experimental" }
 travis-ci = { repository = "CraneStation/cranelift" }
diff --git a/cranelift/codegen/src/verifier/mod.rs b/cranelift/codegen/src/verifier/mod.rs
index 694e5e46de..276e43adf9 100644
--- a/cranelift/codegen/src/verifier/mod.rs
+++ b/cranelift/codegen/src/verifier/mod.rs
@@ -267,8 +267,6 @@ struct Verifier<'a> {
     expected_cfg: ControlFlowGraph,
     expected_domtree: DominatorTree,
     isa: Option<&'a dyn TargetIsa>,
-    // To be removed when #796 is completed.
-    verify_encodable_as_bb: bool,
 }
 
 impl<'a> Verifier<'a> {
@@ -280,7 +278,6 @@ impl<'a> Verifier<'a> {
             expected_cfg,
             expected_domtree,
             isa: fisa.isa,
-            verify_encodable_as_bb: std::env::var("CRANELIFT_BB").is_ok(),
         }
     }
 
@@ -473,12 +470,8 @@ impl<'a> Verifier<'a> {
 
     /// Check that the given EBB can be encoded as a BB, by checking that only
     /// branching instructions are ending the EBB.
+    #[cfg(feature = "basic-blocks")]
     fn encodable_as_bb(&self, ebb: Ebb, errors: &mut VerifierErrors) -> VerifierStepResult<()> {
-        // Skip this verification if the environment variable is not set.
-        if !self.verify_encodable_as_bb {
-            return Ok(());
-        };
-
         let dfg = &self.func.dfg;
         let inst_iter = self.func.layout.ebb_insts(ebb);
         // Skip non-branching instructions.
@@ -1794,6 +1787,8 @@ impl<'a> Verifier<'a> {
                 self.verify_encoding(inst, errors)?;
                 self.immediate_constraints(inst, errors)?;
             }
+
+            #[cfg(feature = "basic-blocks")]
             self.encodable_as_bb(ebb, errors)?;
         }