fix(compiler): Move operations in scf.for reinstantiation pattern before replacement

The reinstantianting rewrite pattern for `scf.for` operations,
`TypeConvertingReinstantiationPattern<scf::ForOp, false>`, calls
`mlir::ConversionPatternRewriter::replaceOpWithNewOp()` before moving
the operations of the original loop to the newly created loop. Since
`replaceOpWithNewOp()` indirectly marks all operations of the old loop
as ignored for dialect conversion, the dialect converter never
descends recursively into the newly created loop.

This causes operations that are illegal to be preserved, which results
in illegal IR after dialect conversion.

This commit splits the replacement into three steps:

  1. Creation of the new loop via
     mlir::ConversionPatternRewriter::create()`
  2. Moving operations from the old loop to the newly created one
  3. Replacement of the original loop with the results of the new one
     via `mlir::ConversionPatternRewriter::replaceOp()`

This causes the operations of the loops not to be ignored and fixes
dialect conversion.

compilers/concrete-compiler/compiler/lib/Conversion/Utils/Dialects/SCF.cpp

@@ -14,8 +14,8 @@ TypeConvertingReinstantiationPattern<scf::ForOp, false>::matchAndRewrite(
     scf::ForOp oldOp, mlir::OpConversionPattern<scf::ForOp>::OpAdaptor adaptor,
     mlir::ConversionPatternRewriter &rewriter) const {
   // Create new for loop with empty body, but converted iter args
-  scf::ForOp newForOp = rewriter.replaceOpWithNewOp<scf::ForOp>(
-      oldOp, adaptor.getLowerBound(), adaptor.getUpperBound(),
+  scf::ForOp newForOp = rewriter.create<scf::ForOp>(
+      oldOp.getLoc(), adaptor.getLowerBound(), adaptor.getUpperBound(),
       adaptor.getStep(), adaptor.getInitArgs(),
       [&](OpBuilder &builder, Location loc, Value iv, ValueRange args) {});
 
@@ -35,6 +35,8 @@ TypeConvertingReinstantiationPattern<scf::ForOp, false>::matchAndRewrite(
                                newForOp.getRegion());
   }
 
+  rewriter.replaceOp(oldOp, newForOp.getResults());
+
   return mlir::success();
 }
 } // namespace concretelang