[MemCpyOpt] Fixing Incorrect Code Motion while Handling Aggregate Type Values

lenary · lenary · commit 7fc698b06acd · 2019-10-21T10:00:34.000Z
Summary: When MemCpyOpt is handling aggregate type values, if an instruction (let's call it P) between the targeting load (L) and store (S) clobbers the source pointer of L, it will try to hoist S before P. This process will also hoist S's data dependency instructions. However, the current implementation has a bug that if one of S's dependency instructions is //also// a user of P, MemCpyOpt will not prevent it from being hoisted above P and cause a use-before-define error. For example, in the newly added test file (i.e. `aggregate-type-crash.ll`), it will try to hoist both `store %my_struct %1, %my_struct* %3` and its dependent, `%3 = bitcast i8* %2 to %my_struct*`, above `%2 = call i8* @my_malloc(%my_struct* %0)`. Creating the following BB: ``` entry: %1 = bitcast i8* %4 to %my_struct* %2 = bitcast %my_struct* %1 to i8* %3 = bitcast %my_struct* %0 to i8* call void @llvm.memcpy.p0i8.p0i8.i64(i8* align 4 %2, i8* align 4 %3, i64 8, i1 false) %4 = call i8* @my_malloc(%my_struct* %0) ret void ``` Where there is a use-before-define error between `%1` and `%4`. Update: The compiler for the Pony Programming Language [also encounter the same bug](ponylang/ponyc#3140) Patch by Min-Yih Hsu (myhsu) Reviewers: eugenis, pcc, dblaikie, dneilson, t.p.northover, lattner Reviewed By: eugenis Subscribers: lenary, hiraditya, llvm-commits Tags: #llvm Differential Revision: https://reviews.llvm.org/D66060 git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@375403 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Transforms/Scalar/MemCpyOptimizer.cpp b/lib/Transforms/Scalar/MemCpyOptimizer.cpp
@@ -513,9 +513,13 @@ static bool moveUp(AliasAnalysis &AA, StoreInst *SI, Instruction *P,
 
     ToLift.push_back(C);
     for (unsigned k = 0, e = C->getNumOperands(); k != e; ++k)
-      if (auto *A = dyn_cast<Instruction>(C->getOperand(k)))
-        if (A->getParent() == SI->getParent())
+      if (auto *A = dyn_cast<Instruction>(C->getOperand(k))) {
+        if (A->getParent() == SI->getParent()) {
+          // Cannot hoist user of P above P
+          if(A == P) return false;
           Args.insert(A);
+        }
+      }
   }
 
   // We made it, we need to lift
diff --git a/test/Transforms/MemCpyOpt/aggregate-type-crash.ll b/test/Transforms/MemCpyOpt/aggregate-type-crash.ll
@@ -0,0 +1,30 @@
+; RUN: opt -memcpyopt -S -o - < %s | FileCheck %s
+
+target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-apple-macosx10.14.0"
+
+%my_struct = type { i8, i32 }
+
+; Function Attrs: inaccessiblemem_or_argmemonly
+declare noalias i8* @my_malloc(%my_struct*) #0
+
+define void @my_func(%my_struct* %0) {
+entry:
+; CHECK: entry:
+  %1 = load %my_struct, %my_struct* %0
+  %2 = call i8* @my_malloc(%my_struct* %0)
+  %3 = bitcast i8* %2 to %my_struct*
+  store %my_struct %1, %my_struct* %3
+; CHECK-NOT: call void @llvm.memcpy.{{.*}}.{{.*}}.{{.*}}
+  ret void
+}
+
+attributes #0 = { inaccessiblemem_or_argmemonly }
+
+!llvm.module.flags = !{!0, !1, !2}
+!llvm.ident = !{!3}
+
+!0 = !{i32 2, !"SDK Version", [2 x i32] [i32 10, i32 14]}
+!1 = !{i32 1, !"wchar_size", i32 4}
+!2 = !{i32 7, !"PIC Level", i32 2}
+!3 = !{!"Apple LLVM version 10.0.1 (clang-1001.0.46.4)"}
