emitCudaKernel: avoid relying on isl set variable names in domain of schedule

In particular, call Scop::makeIslAffFromStmtExpr, which takes
care of the mapping between set dimensions and their names,
instead of assuming that the variable names of the domain
of the schedule were preserved through the entire
AST generation process.

This only handles half of the reliance on the preservation
of isl set variable names in the scheduler.
The other half will be handled by the next commit.

Author: Sven Verdoolaege

include/tc/core/polyhedral/cuda/codegen.h

@@ -19,6 +19,7 @@
 #include <string>
 #include <unordered_map>
 
+#include "tc/core/halide2isl.h"
 #include "tc/core/polyhedral/cuda/mapped_scop.h"
 #include "tc/core/polyhedral/scop.h"
 #include "tc/external/isl.h"
@@ -103,6 +104,16 @@ struct CodegenStatementContext : CodegenContext {
     }
     return result;
   }
+  // Make an affine function from a Halide Expr that is defined
+  // over the instance set of the statement corresponding to
+  // the AST node of this CodegenStatementContext.  Return a
+  // null isl::aff if the expression is not affine.  Fail if any
+  // of the variables does not correspond to a parameter or
+  // an instance identifier of the statement.
+  isl::aff makeIslAffFromExpr(const Halide::Expr& e) const {
+    auto space = iteratorMap().get_space().params();
+    return scop().makeIslAffFromStmtExpr(statementId(), space, e);
+  }
 
   isl::id astNodeId;
 };

src/core/polyhedral/cuda/codegen.cc

@@ -21,7 +21,6 @@
 #include <utility>
 
 #include "tc/core/flags.h"
-#include "tc/core/halide2isl.h"
 #include "tc/core/islpp_wrap.h"
 #include "tc/core/libraries.h"
 #include "tc/core/polyhedral/codegen.h"
@@ -458,11 +457,10 @@ namespace detail {
 isl::pw_aff makeAffFromMappedExpr(
     const Halide::Expr& expr,
     const CodegenStatementContext& context) {
-  auto space = context.iteratorMap().get_space().range();
   // We only expect this to be called on encountering a free
   // variable. Compound expressions should be emitted as Halide.
   CHECK(expr.as<Halide::Internal::Variable>());
-  auto aff = halide2isl::makeIslAffFromExpr(space, expr);
+  auto aff = context.makeIslAffFromExpr(expr);
   auto pwaff = isl::pw_aff(aff).pullback(context.iteratorMap());
   return pwaff;
 }
@@ -492,8 +490,7 @@ isl::multi_aff makeMultiAffAccess(
 
   auto ma = isl::multi_aff::zero(space);
   for (size_t i = 0; i < subscripts.size(); ++i) {
-    ma = ma.set_aff(
-        i, halide2isl::makeIslAffFromExpr(domainSpace, subscripts[i]));
+    ma = ma.set_aff(i, context.makeIslAffFromExpr(subscripts[i]));
   }
   return ma;
 }