Make passes assert their dependencies consistently. (#156)

* Make passes assert their dependencies consistently.

This avoids ambiguity about whose responsibility it is to run
to compute cfg, domtree, and loop_analysis data.

* Reset the `valid` flag in DominatorTree's `clear()`.

* Remove the redundant assert from DominatorTree::with_function.

* Remove the message strings from obvious asserts.

This avoids having them spill out into multiple lines.

* Refactor calls to `compute` on `Context` objects into helper functions.

cranelift/src/filetest/legalizer.rs

@@ -40,7 +40,7 @@ impl SubTest for TestLegalizer {
         comp_ctx.func = func.into_owned();
         let isa = context.isa.expect("legalizer needs an ISA");
 
-        comp_ctx.flowgraph();
+        comp_ctx.compute_cfg();
         comp_ctx.legalize(isa).map_err(|e| {
             pretty_error(&comp_ctx.func, context.isa, e)
         })?;

cranelift/src/filetest/licm.rs

@@ -38,6 +38,8 @@ impl SubTest for TestLICM {
         let mut comp_ctx = cretonne::Context::new();
         comp_ctx.func = func.into_owned();
 
+        comp_ctx.flowgraph();
+        comp_ctx.compute_loop_analysis();
         comp_ctx.licm();
         comp_ctx.verify(context.isa).map_err(|e| {
             pretty_error(&comp_ctx.func, context.isa, Into::into(e))

cranelift/src/filetest/regalloc.rs

@@ -44,11 +44,12 @@ impl SubTest for TestRegalloc {
         let mut comp_ctx = cretonne::Context::new();
         comp_ctx.func = func.into_owned();
 
-        comp_ctx.flowgraph();
+        comp_ctx.compute_cfg();
         // TODO: Should we have an option to skip legalization?
         comp_ctx.legalize(isa).map_err(|e| {
             pretty_error(&comp_ctx.func, context.isa, e)
         })?;
+        comp_ctx.compute_domtree();
         comp_ctx.regalloc(isa).map_err(|e| {
             pretty_error(&comp_ctx.func, context.isa, e)
         })?;

cranelift/src/filetest/simple_gvn.rs

@@ -38,6 +38,7 @@ impl SubTest for TestSimpleGVN {
         let mut comp_ctx = cretonne::Context::new();
         comp_ctx.func = func.into_owned();
 
+        comp_ctx.flowgraph();
         comp_ctx.simple_gvn();
         comp_ctx.verify(context.isa).map_err(|e| {
             pretty_error(&comp_ctx.func, context.isa, Into::into(e))

cranelift/src/wasm.rs

@@ -158,6 +158,8 @@ fn handle_module(
             context.verify(None).map_err(|err| {
                 pretty_verifier_error(&context.func, None, err)
             })?;
+            context.flowgraph();
+            context.compute_loop_analysis();
             context.licm();
             context.verify(None).map_err(|err| {
                 pretty_verifier_error(&context.func, None, err)