[TailCallElim] Don’t mark llvm.stackrestore with tail-call (llvm#101352)

This is to teach tailcallelim transformation not to mark
llvm.stackrestore with tail-call, as the intrinsic call can modify
unescaped allocas from the caller.
 
This fixes a problem found with our downstream testing. The problem can
also be shown when running the test case
llvm/test/Transforms/MemCpyOpt/stackrestore with passes=”tailcallelim,
memcpyopt”.

Author: scui-ibm

llvm/lib/Transforms/Scalar/TailRecursionElimination.cpp

@@ -243,6 +243,12 @@ static bool markTails(Function &F, OptimizationRemarkEmitter *ORE) {
           isa<PseudoProbeInst>(&I))
         continue;
 
+      // Bail out for intrinsic stackrestore call because it can modify
+      // unescaped allocas.
+      if (auto *II = dyn_cast<IntrinsicInst>(CI))
+        if (II->getIntrinsicID() == Intrinsic::stackrestore)
+          continue;
+
       // Special-case operand bundles "clang.arc.attachedcall", "ptrauth", and
       // "kcfi".
       bool IsNoTail = CI->isNoTailCall() ||

llvm/test/Transforms/TailCallElim/stackrestore.ll

@@ -0,0 +1,14 @@
+; RUN: opt -S -passes=tailcallelim < %s | FileCheck %s
+
+define void @foo() {
+; CHECK-LABEL: define void @foo()
+; CHECK-NOT:   tail call void @llvm.stackrestore.p0
+;
+entry:
+  %0 = call ptr @llvm.stacksave.p0()
+  call void @llvm.stackrestore.p0(ptr %0)
+  ret void
+}
+
+declare ptr @llvm.stacksave.p0()
+declare void @llvm.stackrestore.p0(ptr)