From 768e62f6c7541439e2edc18dad5fb3846d2e05f9 Mon Sep 17 00:00:00 2001
From: Yong He <yonghe@outlook.com>
Date: Mon, 10 Oct 2022 15:59:45 -0700
Subject: Support multi-level break + single-return conversion + general
 inline. (#2436)

* Support multi-level break.

* Single return.

* Add test for inlining `void` return-type functions.

Co-authored-by: Yong He <yhe@nvidia.com>
---
 source/slang/slang-ir-single-return.cpp | 103 ++++++++++++++++++++++++++++++++
 1 file changed, 103 insertions(+)
 create mode 100644 source/slang/slang-ir-single-return.cpp

(limited to 'source/slang/slang-ir-single-return.cpp')

diff --git a/source/slang/slang-ir-single-return.cpp b/source/slang/slang-ir-single-return.cpp
new file mode 100644
index 000000000..a00066556
--- /dev/null
+++ b/source/slang/slang-ir-single-return.cpp
@@ -0,0 +1,103 @@
+// slang-ir-single-return.cpp
+#include "slang-ir-single-return.h"
+#include "slang-ir.h"
+#include "slang-ir-clone.h"
+#include "slang-ir-insts.h"
+#include "slang-ir-inst-pass-base.h"
+#include "slang-ir-eliminate-multilevel-break.h"
+#include "slang-ir-simplify-cfg.h"
+
+namespace Slang
+{
+
+struct SingleReturnContext : public InstPassBase
+{
+    SingleReturnContext(IRModule* inModule)
+        : InstPassBase(inModule)
+    {}
+    void processFunc(IRGlobalValueWithCode* func)
+    {
+        SharedIRBuilder sharedBuilder;
+        sharedBuilder.init(module);
+        IRBuilder builder(&sharedBuilder);
+        simplifyCFG(func);
+
+        // We make use of the `eliminate-multi-level-break` pass to implement the transformation.
+        // To be able to do that, we need to prepare `func` so that the entire function body
+        // is wrapped in a trivial loop and turn all `return`s into `break`s out of the outter most
+        // loop.
+        builder.setInsertInto(func);
+        auto breakBlock = builder.emitBlock();
+        auto returnBlock = builder.emitBlock();
+        builder.setInsertInto(breakBlock);
+        auto resultType = as<IRFuncType>(func->getDataType())->getResultType();
+
+        IRInst* retValParam = nullptr;
+        if (resultType->getOp() != kIROp_VoidType)
+        {
+            retValParam = builder.emitParam(resultType);
+        }
+        builder.emitBranch(returnBlock);
+
+        auto originalStartBlock = func->getFirstBlock();
+        auto loopHeaderBlock = builder.createBlock();
+        loopHeaderBlock->insertBefore(originalStartBlock);
+        builder.setInsertInto(loopHeaderBlock);
+
+        // Move all params into `loopHeaderBlock`.
+        List<IRParam*> params;
+        for (auto param : originalStartBlock->getParams())
+        {
+            params.add(param);
+        }
+        for (auto param : params)
+        {
+            loopHeaderBlock->addParam(param);
+        }
+        auto loopInst = (IRLoop*)builder.emitLoop(originalStartBlock, breakBlock, originalStartBlock);
+
+        // Now replace all return insts as break insts.
+        processChildInstsOfType<IRReturn>(kIROp_Return, func, [&](IRReturn* returnInst)
+            {
+                IRInst* retVal = nullptr;
+                if (returnInst->getOperandCount() == 0)
+                    retVal = builder.getVoidValue();
+                else
+                    retVal = returnInst->getVal();
+                builder.setInsertBefore(returnInst);
+                if (resultType->getOp()==kIROp_VoidType)
+                {
+                    builder.emitBranch(breakBlock);
+                }
+                else
+                {
+                    builder.emitBranch(breakBlock, 1, &retVal);
+                }
+                returnInst->removeAndDeallocate();
+            });
+
+        builder.setInsertInto(returnBlock);
+        if (retValParam)
+            builder.emitReturn(retValParam);
+        else
+            builder.emitReturn();
+
+        // Now run the multi-level-break pass.
+        eliminateMultiLevelBreakForFunc(module, func);
+
+        // Now remove the trivial loop header.
+        SLANG_RELEASE_ASSERT(loopInst->getContinueBlock() == loopInst->getTargetBlock());
+        auto targetBlock = loopInst->getTargetBlock();
+        for (auto param : params)
+            targetBlock->addParam(param);
+        loopHeaderBlock->removeAndDeallocate();
+    }
+};
+
+void convertFuncToSingleReturnForm(IRModule* irModule, IRGlobalValueWithCode* func)
+{
+    SingleReturnContext context(irModule);
+    context.processFunc(func);
+}
+
+} // namespace Slang
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