[DebugInfo] Remove Expr from debug variables used as DenseMap keys

We do keep the fragment part of the expression as it is important
to identify fragments separately.

A variable with less fragments should be considered a superset of
variables with more fragments, but that would require to change a
lot of code.

lib/SILOptimizer/Mandatory/DebugInfoCanonicalizer.cpp

@@ -221,6 +221,9 @@ bool DebugInfoCanonicalizer::process() {
           LLVM_DEBUG(llvm::dbgs() << "        Has no var info?! Skipping!\n");
           continue;
         }
+        // Strip things we don't need in the map.
+        debugInfo->DIExpr = debugInfo->DIExpr.getFragmentPart();
+        debugInfo->Type = {};
 
         // Otherwise, we may have a new debug_value to track. Try to begin
         // tracking it...