From 6b69985da42c6bdbe83127de9653ee795024c8d0 Mon Sep 17 00:00:00 2001
From: Nikita Popov <npopov@redhat.com>
Date: Wed, 26 Jan 2022 11:27:44 +0100
Subject: [PATCH] [MemCpyOpt] Use helper for unwind check

This extends support to byval arguments. It would be further
extended to handle the case of non-captured noalias returns.
---
 llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp   | 24 +++++++++++++++---------
 llvm/test/Transforms/MemCpyOpt/callslot_throw.ll |  6 ++----
 2 files changed, 17 insertions(+), 13 deletions(-)

diff --git a/llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp b/llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp
index 4959125..6698db2 100644
--- a/llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp
+++ b/llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp
@@ -313,15 +313,21 @@ INITIALIZE_PASS_END(MemCpyOptLegacyPass, "memcpyopt", "MemCpy Optimization",
 static bool mayBeVisibleThroughUnwinding(Value *V, Instruction *Start,
                                          Instruction *End) {
   assert(Start->getParent() == End->getParent() && "Must be in same block");
-  if (!Start->getFunction()->doesNotThrow() &&
-      !isa<AllocaInst>(getUnderlyingObject(V))) {
-    for (const Instruction &I :
-         make_range(Start->getIterator(), End->getIterator())) {
-      if (I.mayThrow())
-        return true;
-    }
-  }
-  return false;
+  // Function can't unwind, so it also can't be visible through unwinding.
+  if (Start->getFunction()->doesNotThrow())
+    return false;
+
+  // Object is not visible on unwind.
+  // TODO: Support RequiresNoCaptureBeforeUnwind case.
+  bool RequiresNoCaptureBeforeUnwind;
+  if (isNotVisibleOnUnwind(getUnderlyingObject(V),
+                           RequiresNoCaptureBeforeUnwind) &&
+      !RequiresNoCaptureBeforeUnwind)
+    return false;
+
+  // Check whether there are any unwinding instructions in the range.
+  return any_of(make_range(Start->getIterator(), End->getIterator()),
+                [](const Instruction &I) { return I.mayThrow(); });
 }
 
 void MemCpyOptPass::eraseInstruction(Instruction *I) {
diff --git a/llvm/test/Transforms/MemCpyOpt/callslot_throw.ll b/llvm/test/Transforms/MemCpyOpt/callslot_throw.ll
index ce0d575..62b6fcf 100644
--- a/llvm/test/Transforms/MemCpyOpt/callslot_throw.ll
+++ b/llvm/test/Transforms/MemCpyOpt/callslot_throw.ll
@@ -40,14 +40,12 @@ entry:
   ret void
 }
 
-; TODO: byval argument is not visible on unwind.
+; byval argument is not visible on unwind.
 define void @test_byval(i32* nocapture noalias dereferenceable(4) byval(i32) %x) {
 ; CHECK-LABEL: @test_byval(
 ; CHECK-NEXT:  entry:
 ; CHECK-NEXT:    [[T:%.*]] = alloca i32, align 4
-; CHECK-NEXT:    call void @may_throw(i32* nonnull [[T]])
-; CHECK-NEXT:    [[LOAD:%.*]] = load i32, i32* [[T]], align 4
-; CHECK-NEXT:    store i32 [[LOAD]], i32* [[X:%.*]], align 4
+; CHECK-NEXT:    call void @may_throw(i32* nonnull [[X:%.*]])
 ; CHECK-NEXT:    ret void
 ;
 entry:
-- 
2.7.4