Support unwinding from inline assembly

I've taken the following steps to add unwinding support from inline assembly:

1) Add a new `unwind` "attribute" (like `sideeffect`) to the asm syntax:

```
invoke void asm sideeffect unwind "call thrower", "~{dirflag},~{fpsr},~{flags}"()
    to label %exit unwind label %uexit
```

2.) Add Bitcode writing/reading support + LLVM-IR parsing.

3.) Emit EHLabels around inline assembly lowering (SelectionDAGBuilder + GlobalISel) when `InlineAsm::canThrow` is enabled.

4.) Tweak InstCombineCalls/InlineFunction pass to not mark inline assembly "calls" as nounwind.

5.) Add clang support by introducing a new clobber: "unwind", which lower to the `canThrow` being enabled.

6.) Don't allow unwinding callbr.

Reviewed By: Amanieu

Differential Revision: https://reviews.llvm.org/D95745

1 files changed, 80 insertions, 43 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
index 4b2d811..e9eea5b 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
@@ -2873,7 +2873,7 @@ void SelectionDAGBuilder::visitInvoke(const InvokeInst &I) {
   const Value *Callee(I.getCalledOperand());
   const Function *Fn = dyn_cast<Function>(Callee);
   if (isa<InlineAsm>(Callee))
-    visitInlineAsm(I);
+    visitInlineAsm(I, EHPadBB);
   else if (Fn && Fn->isIntrinsic()) {
     switch (Fn->getIntrinsicID()) {
     default:
@@ -7281,36 +7281,72 @@ void SelectionDAGBuilder::visitVectorPredicationIntrinsic(
   setValue(&VPIntrin, Result);
 }
 
-std::pair<SDValue, SDValue>
-SelectionDAGBuilder::lowerInvokable(TargetLowering::CallLoweringInfo &CLI,
-                                    const BasicBlock *EHPadBB) {
+SDValue SelectionDAGBuilder::lowerStartEH(SDValue Chain,
+                                          const BasicBlock *EHPadBB,
+                                          MCSymbol *&BeginLabel) {
   MachineFunction &MF = DAG.getMachineFunction();
   MachineModuleInfo &MMI = MF.getMMI();
-  MCSymbol *BeginLabel = nullptr;
 
-  if (EHPadBB) {
-    // Insert a label before the invoke call to mark the try range.  This can be
-    // used to detect deletion of the invoke via the MachineModuleInfo.
-    BeginLabel = MMI.getContext().createTempSymbol();
+  // Insert a label before the invoke call to mark the try range.  This can be
+  // used to detect deletion of the invoke via the MachineModuleInfo.
+  BeginLabel = MMI.getContext().createTempSymbol();
 
-    // For SjLj, keep track of which landing pads go with which invokes
-    // so as to maintain the ordering of pads in the LSDA.
-    unsigned CallSiteIndex = MMI.getCurrentCallSite();
-    if (CallSiteIndex) {
-      MF.setCallSiteBeginLabel(BeginLabel, CallSiteIndex);
-      LPadToCallSiteMap[FuncInfo.MBBMap[EHPadBB]].push_back(CallSiteIndex);
+  // For SjLj, keep track of which landing pads go with which invokes
+  // so as to maintain the ordering of pads in the LSDA.
+  unsigned CallSiteIndex = MMI.getCurrentCallSite();
+  if (CallSiteIndex) {
+    MF.setCallSiteBeginLabel(BeginLabel, CallSiteIndex);
+    LPadToCallSiteMap[FuncInfo.MBBMap[EHPadBB]].push_back(CallSiteIndex);
 
-      // Now that the call site is handled, stop tracking it.
-      MMI.setCurrentCallSite(0);
-    }
+    // Now that the call site is handled, stop tracking it.
+    MMI.setCurrentCallSite(0);
+  }
+
+  return DAG.getEHLabel(getCurSDLoc(), Chain, BeginLabel);
+}
 
+SDValue SelectionDAGBuilder::lowerEndEH(SDValue Chain, const InvokeInst *II,
+                                        const BasicBlock *EHPadBB,
+                                        MCSymbol *BeginLabel) {
+  assert(BeginLabel && "BeginLabel should've been set");
+
+  MachineFunction &MF = DAG.getMachineFunction();
+  MachineModuleInfo &MMI = MF.getMMI();
+
+  // Insert a label at the end of the invoke call to mark the try range.  This
+  // can be used to detect deletion of the invoke via the MachineModuleInfo.
+  MCSymbol *EndLabel = MMI.getContext().createTempSymbol();
+  Chain = DAG.getEHLabel(getCurSDLoc(), Chain, EndLabel);
+
+  // Inform MachineModuleInfo of range.
+  auto Pers = classifyEHPersonality(FuncInfo.Fn->getPersonalityFn());
+  // There is a platform (e.g. wasm) that uses funclet style IR but does not
+  // actually use outlined funclets and their LSDA info style.
+  if (MF.hasEHFunclets() && isFuncletEHPersonality(Pers)) {
+    assert(II && "II should've been set");
+    WinEHFuncInfo *EHInfo = MF.getWinEHFuncInfo();
+    EHInfo->addIPToStateRange(II, BeginLabel, EndLabel);
+  } else if (!isScopedEHPersonality(Pers)) {
+    assert(EHPadBB);
+    MF.addInvoke(FuncInfo.MBBMap[EHPadBB], BeginLabel, EndLabel);
+  }
+
+  return Chain;
+}
+
+std::pair<SDValue, SDValue>
+SelectionDAGBuilder::lowerInvokable(TargetLowering::CallLoweringInfo &CLI,
+                                    const BasicBlock *EHPadBB) {
+  MCSymbol *BeginLabel = nullptr;
+
+  if (EHPadBB) {
     // Both PendingLoads and PendingExports must be flushed here;
     // this call might not return.
     (void)getRoot();
-    DAG.setRoot(DAG.getEHLabel(getCurSDLoc(), getControlRoot(), BeginLabel));
-
+    DAG.setRoot(lowerStartEH(getControlRoot(), EHPadBB, BeginLabel));
     CLI.setChain(getRoot());
   }
+
   const TargetLowering &TLI = DAG.getTargetLoweringInfo();
   std::pair<SDValue, SDValue> Result = TLI.LowerCallTo(CLI);
 
@@ -7332,22 +7368,8 @@ SelectionDAGBuilder::lowerInvokable(TargetLowering::CallLoweringInfo &CLI,
   }
 
   if (EHPadBB) {
-    // Insert a label at the end of the invoke call to mark the try range.  This
-    // can be used to detect deletion of the invoke via the MachineModuleInfo.
-    MCSymbol *EndLabel = MMI.getContext().createTempSymbol();
-    DAG.setRoot(DAG.getEHLabel(getCurSDLoc(), getRoot(), EndLabel));
-
-    // Inform MachineModuleInfo of range.
-    auto Pers = classifyEHPersonality(FuncInfo.Fn->getPersonalityFn());
-    // There is a platform (e.g. wasm) that uses funclet style IR but does not
-    // actually use outlined funclets and their LSDA info style.
-    if (MF.hasEHFunclets() && isFuncletEHPersonality(Pers)) {
-      assert(CLI.CB);
-      WinEHFuncInfo *EHInfo = DAG.getMachineFunction().getWinEHFuncInfo();
-      EHInfo->addIPToStateRange(cast<InvokeInst>(CLI.CB), BeginLabel, EndLabel);
-    } else if (!isScopedEHPersonality(Pers)) {
-      MF.addInvoke(FuncInfo.MBBMap[EHPadBB], BeginLabel, EndLabel);
-    }
+    DAG.setRoot(lowerEndEH(getRoot(), cast_or_null<InvokeInst>(CLI.CB), EHPadBB,
+                           BeginLabel));
   }
 
   return Result;
@@ -8317,7 +8339,8 @@ public:
 } // end anonymous namespace
 
 /// visitInlineAsm - Handle a call to an InlineAsm object.
-void SelectionDAGBuilder::visitInlineAsm(const CallBase &Call) {
+void SelectionDAGBuilder::visitInlineAsm(const CallBase &Call,
+                                         const BasicBlock *EHPadBB) {
   const InlineAsm *IA = cast<InlineAsm>(Call.getCalledOperand());
 
   /// ConstraintOperands - Information about all of the constraints.
@@ -8405,19 +8428,28 @@ void SelectionDAGBuilder::visitInlineAsm(const CallBase &Call) {
     ExtraInfo.update(T);
   }
 
-
   // We won't need to flush pending loads if this asm doesn't touch
   // memory and is nonvolatile.
   SDValue Flag, Chain = (HasSideEffect) ? getRoot() : DAG.getRoot();
 
+  bool EmitEHLabels = isa<InvokeInst>(Call) && IA->canThrow();
+  if (EmitEHLabels) {
+    assert(EHPadBB && "InvokeInst must have an EHPadBB");
+  }
   bool IsCallBr = isa<CallBrInst>(Call);
-  if (IsCallBr) {
-    // If this is a callbr we need to flush pending exports since inlineasm_br
-    // is a terminator. We need to do this before nodes are glued to
-    // the inlineasm_br node.
+
+  if (IsCallBr || EmitEHLabels) {
+    // If this is a callbr or invoke we need to flush pending exports since
+    // inlineasm_br and invoke are terminators.
+    // We need to do this before nodes are glued to the inlineasm_br node.
     Chain = getControlRoot();
   }
 
+  MCSymbol *BeginLabel = nullptr;
+  if (EmitEHLabels) {
+    Chain = lowerStartEH(Chain, EHPadBB, BeginLabel);
+  }
+
   // Second pass over the constraints: compute which constraint option to use.
   for (SDISelAsmOperandInfo &OpInfo : ConstraintOperands) {
     // If this is an output operand with a matching input operand, look up the
@@ -8808,8 +8840,13 @@ void SelectionDAGBuilder::visitInlineAsm(const CallBase &Call) {
   if (!OutChains.empty())
     Chain = DAG.getNode(ISD::TokenFactor, getCurSDLoc(), MVT::Other, OutChains);
 
+  if (EmitEHLabels) {
+    Chain = lowerEndEH(Chain, cast<InvokeInst>(&Call), EHPadBB, BeginLabel);
+  }
+
   // Only Update Root if inline assembly has a memory effect.
-  if (ResultValues.empty() || HasSideEffect || !OutChains.empty() || IsCallBr)
+  if (ResultValues.empty() || HasSideEffect || !OutChains.empty() || IsCallBr ||
+      EmitEHLabels)
     DAG.setRoot(Chain);
 }