[IR] Don't assume readnone/readonly intrinsics are willreturn

[nikic]

Summary

This removes our "temporary" hack to assume that readnone/readonly intrinsics are also willreturn. An explicit willreturn annotation, usually via default intrinsic attributes, is now required.

Depends on D137557, D137623, D137629.

[nikic]

llvm/lib/Transforms/Utils/Local.cpp

459

These are intrinsics for which the current readnone -> willreturn assumption is incorrect, but optimizations currently rely on it. Needs to be addressed in a followup.

[jdoerfert]

LG, removes the hack for all but 4 intrinsics. Thanks for getting rid of it.

llvm/lib/IR/Instruction.cpp

 }
 
 bool Instruction::willReturn() const {
   // Volatile store isn't guaranteed to return; see LangRef.
   if (auto *SI = dyn_cast<StoreInst>(this))
     return !SI->isVolatile();
 
   if (const auto *CB = dyn_cast<CallBase>(this))
-    // FIXME: Temporarily assume that all side-effect free intrinsics will
-    // return. Remove this workaround once all intrinsics are appropriately
-    // annotated.
-    return CB->hasFnAttr(Attribute::WillReturn) ||
-           (isa<IntrinsicInst>(CB) && CB->onlyReadsMemory());
+    return CB->hasFnAttr(Attribute::WillReturn);
   return true;
 }
 
 bool Instruction::isLifetimeStartOrEnd() const {
   auto *II = dyn_cast<IntrinsicInst>(this);
   if (!II)
     return false;
   Intrinsic::ID ID = II->getIntrinsicID();

llvm/lib/Transforms/Utils/Local.cpp

 #include "llvm/IR/GetElementPtrTypeIterator.h"
 #include "llvm/IR/GlobalObject.h"
 #include "llvm/IR/IRBuilder.h"
 #include "llvm/IR/InstrTypes.h"
 #include "llvm/IR/Instruction.h"
 #include "llvm/IR/Instructions.h"
 #include "llvm/IR/IntrinsicInst.h"
 #include "llvm/IR/Intrinsics.h"
+#include "llvm/IR/IntrinsicsWebAssembly.h"
 #include "llvm/IR/LLVMContext.h"
 #include "llvm/IR/MDBuilder.h"
 #include "llvm/IR/Metadata.h"
 #include "llvm/IR/Module.h"
 #include "llvm/IR/PatternMatch.h"
 #include "llvm/IR/Type.h"
 #include "llvm/IR/Use.h"
 #include "llvm/IR/User.h"
if (DLI->getLabel())
       return false;
     return true;
   }
 
   if (auto *CB = dyn_cast<CallBase>(I))
     if (isRemovableAlloc(CB, TLI))
       return true;
 
-  if (!I->willReturn())
+  if (!I->willReturn()) {
+    auto *II = dyn_cast<IntrinsicInst>(I);
+    if (!II)
       return false;
 
+    // TODO: These intrinsics are not safe to remove, because this may remove
+    // a well-defined trap.
+    switch (II->getIntrinsicID()) {
+    case Intrinsic::wasm_trunc_signed:
+    case Intrinsic::wasm_trunc_unsigned:
+    case Intrinsic::ptrauth_auth:
+    case Intrinsic::ptrauth_resign:
+    case Intrinsic::ptrauth_sign:
+      return true;
+    default:
+      return false;
+    }
+  }
+
   if (!I->mayHaveSideEffects())
     return true;
 
   // Special case intrinsics that "may have side effects" but can be deleted
   // when dead.
   if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) {
     // Safe to delete llvm.stacksave and launder.invariant.group if dead.
     if (II->getIntrinsicID() == Intrinsic::stacksave ||