Initial support for differentiating existential types (#3111)

* Merge

* WIP: Complete auto-diff logic for existential types

* Revert "Add compiler option for generating representative hash"

This reverts commit 13b09ef4621e73844c96d64d9c111a8ed0d45aae.

* More fixes for fwd-mode AD on existential types

* Add anyValueSize inference pass

* Fix checking of `Differential.Differential==Differential`

* In-progress: infer any-value-size for existential types

* Existentials now work in forward-mode

* Overhaul handling of existential AD types. Fwd-mode works, reverse-mode requires front-end changes

* Reverse-mode now works on existentials

* Cleanup

* Remove diff rules for create existential object for now

* Revert treat-as-differentiable changes

* Fixes

* More fixes

* Cleanup

* more cleanup

* signed/unsigned

* Revert "Cleanup"

This reverts commit e4f7d71f07bb207736f90708961eeecd09a1b652.

* Cleanup (again)

* Remove public/export/keep-alive on null differential after AD pass

* Minor fix

* Update dictionary accessors

* Keep export decoration

* More fixes + Support for `kIROp_PackAnyValue`

* Merge upstream

* Update expected-failure.txt

1 files changed, 15 insertions, 5 deletions

diff --git a/source/slang/slang-ir-ssa.cpp b/source/slang/slang-ir-ssa.cpp
index 18eba677e..730943bf8 100644
--- a/source/slang/slang-ir-ssa.cpp
+++ b/source/slang/slang-ir-ssa.cpp
@@ -412,7 +412,7 @@ PhiInfo* addPhi(
     {
         valueType = context->getBuilder()->getRateQualifiedType(rate, valueType);
     }
-    IRParam* phi = builder->createParam(valueType);
+    IRParam* phi = builder->emitParam(valueType);
     cloneRelevantDecorations(var, phi);
 
     RefPtr<PhiInfo> phiInfo = new PhiInfo();
@@ -503,6 +503,7 @@ IRInst* tryRemoveTrivialPhi(
     // replace uses of the phi (including its possible uses
     // of itself) with the unique non-phi value.
     phi->replaceUsesWith(same);
+    phi->removeAndDeallocate();
 
     // Clear out the operands to the phi, since they won't
     // actually get used in the program any more.
@@ -849,11 +850,12 @@ void processBlock(
     // leave them as-is, or replace them with a value
     // that we look up with local/global value numbering
 
-    IRInst* next = nullptr;
-    for (auto ii = block->getFirstInst(); ii; ii = next)
-    {
-        next = ii->getNextInst();
+    List<IRInst*> workList;
+    for (auto ii = block->getFirstInst(); ii; ii = ii->getNextInst())
+        workList.add(ii);
 
+    for (auto& ii : workList)
+    {
         // Any new instructions we create to represent
         // the new value will get inserted before whatever
         // instruction we are working with.
@@ -1117,6 +1119,14 @@ bool constructSSA(ConstructSSAContext* context)
     {
         auto blockInfo = *context->blockInfos.tryGetValue(bb);
 
+        // First remove phis from their parent blocks.
+        for (auto phiInfo : blockInfo->phis)
+            if (!phiInfo->replacement)
+                phiInfo->phi->removeFromParent();
+
+        // Then, add them back in a consistent order, and add predecessor
+        // args in the same order.
+        // 
         for (auto phiInfo : blockInfo->phis)
         {
             // If we replaced this phi with another value,