More control flow simplifications. (#2673)

* More control flow and Phi param simplifications.

* Fix.

* Fix gcc error.

* Fix.

* More IR cleanup.

* Fix bug in phi param dce + ifelse simplify.

* Propagate and DCE side-effect-free functions.

* Enhance CFG simplifcation to remove loops with no side effects.

* Fix.

* Fixes.

* Fix tests. Add [__AlwaysFoldIntoUseSite] for rayPayloadLocation.

* More cleanup.

* Fixes.

* Fix.

---------

Co-authored-by: Yong He <yhe@nvidia.com>

1 files changed, 186 insertions, 0 deletions

diff --git a/source/slang/slang-ir-propagate-func-properties.cpp b/source/slang/slang-ir-propagate-func-properties.cpp
new file mode 100644
index 000000000..f98a77fc7
--- /dev/null
+++ b/source/slang/slang-ir-propagate-func-properties.cpp
@@ -0,0 +1,186 @@
+#include "slang-ir-propagate-func-properties.h"
+
+#include "slang-ir.h"
+#include "slang-ir-insts.h"
+#include "slang-ir-util.h"
+
+
+namespace Slang
+{
+bool propagateFuncProperties(IRModule* module)
+{
+    bool result = false;
+    List<IRFunc*> workList;
+    HashSet<IRFunc*> workListSet;
+
+    auto addToWorkList = [&](IRFunc* f)
+    {
+        if (workListSet.Add(f))
+            workList.add(f);
+    };
+    auto addCallersToWorkList = [&](IRFunc* f)
+    {
+        if (auto g = findOuterGeneric(f))
+        {
+            for (auto use = g->firstUse; use; use = use->nextUse)
+            {
+                if (use->getUser()->getOp() == kIROp_Specialize)
+                {
+                    auto specialize = use->getUser();
+                    for (auto iuse = specialize->firstUse; iuse; iuse = iuse->nextUse)
+                    {
+                        if (auto userFunc = getParentFunc(iuse->getUser()))
+                            addToWorkList(userFunc);
+                    }
+                }
+            }
+            return;
+        }
+        for (auto use = f->firstUse; use; use = use->nextUse)
+        {
+            if (use->getUser()->getOp() == kIROp_Call)
+            {
+                if (auto userFunc = getParentFunc(use->getUser()))
+                    addToWorkList(userFunc);
+            }
+        }
+    };
+    for (;;)
+    {
+        bool changed = false;
+        workList.clear();
+        workListSet.Clear();
+
+        // Add side effect free functions and their transitive callers to work list.
+        for (auto inst : module->getGlobalInsts())
+        {
+            auto genericInst = as<IRGeneric>(inst);
+            if (genericInst)
+            {
+                inst = findGenericReturnVal(genericInst);
+            }
+            if (auto func = as<IRFunc>(inst))
+            {
+                if (func->findDecoration<IRReadNoneDecoration>())
+                {
+                    addCallersToWorkList(func);
+                }
+            }
+        }
+
+        // Add remaining functions to work list.
+        for (auto inst : module->getGlobalInsts())
+        {
+            auto genericInst = as<IRGeneric>(inst);
+            if (genericInst)
+            {
+                inst = findGenericReturnVal(genericInst);
+            }
+            if (auto func = as<IRFunc>(inst))
+            {
+                addToWorkList(func);
+            }
+        }
+
+        IRBuilder builder(module);
+
+        for (Index i = 0; i < workList.getCount(); i++)
+        {
+            auto f = workList[i];
+            bool hasSideEffectCall = false;
+            if (f->findDecoration<IRReadNoneDecoration>())
+                continue;
+            // Never propagate to functions without a body.
+            if (f->getFirstBlock() == nullptr)
+                continue;
+            if (f->findDecoration<IRTargetIntrinsicDecoration>())
+                continue;
+            for (auto block : f->getBlocks())
+            {
+                for (auto inst : block->getChildren())
+                {
+                    // Is this inst known to not have global side effect/analyzable?
+                    if (inst->mightHaveSideEffects())
+                    {
+                        switch (inst->getOp())
+                        {
+                        case kIROp_ifElse:
+                        case kIROp_unconditionalBranch:
+                        case kIROp_Switch:
+                        case kIROp_Return:
+                        case kIROp_loop:
+                        case kIROp_Store:
+                        case kIROp_Call:
+                        case kIROp_Param:
+                        case kIROp_Unreachable:
+                            break;
+                        default:
+                            // We have a inst that has side effect and is not understood by this method.
+                            // e.g. bufferStore, discard, etc.
+                            return true;
+                        }
+                    }
+
+                    if (auto call = as<IRCall>(inst))
+                    {
+                        auto callee = getResolvedInstForDecorations(call->getCallee());
+                        switch (callee->getOp())
+                        {
+                        default:
+                            // We are calling an unknown function, so we have to assume
+                            // there are side effects in the call.
+                            hasSideEffectCall = true;
+                            break;
+                        case kIROp_Func:
+                            if (!callee->findDecoration<IRReadNoneDecoration>())
+                            {
+                                hasSideEffectCall = true;
+                                break;
+                            }
+                        }
+                    }
+                    
+                    // Are any operands defined in global scope?
+                    for (UInt o = 0; o < inst->getOperandCount(); o++)
+                    {
+                        auto operand = inst->getOperand(o);
+                        if (getParentFunc(operand) == f)
+                            continue;
+                        if (as<IRConstant>(operand))
+                            continue;
+                        if (as<IRType>(operand))
+                            continue;
+                        switch (operand->getOp())
+                        {
+                        case kIROp_Specialize:
+                        case kIROp_LookupWitness:
+                        case kIROp_StructKey:
+                        case kIROp_WitnessTable:
+                        case kIROp_WitnessTableEntry:
+                        case kIROp_undefined:
+                        case kIROp_Func:
+                            continue;
+                        default:
+                            break;
+                        }
+                        hasSideEffectCall = true;
+                        break;
+                    }
+                }
+                if (hasSideEffectCall)
+                    break;
+            }
+            if (!hasSideEffectCall)
+            {
+                builder.addDecoration(f, kIROp_ReadNoneDecoration);
+                addCallersToWorkList(f);
+                changed = true;
+            }
+        }
+        result |= changed;
+        if (!changed)
+            break;
+    }
+    return result;
+}
+}