[PATCH] D115992: [AA] Handle callbr instructions in alias analysis.

[Ricky Zhou via Phabricator via llvm-commits]

rickyz created this revision.
rickyz added reviewers: nikic, dfukalov.
Herald added subscribers: jeroen.dobbelaere, hiraditya.
rickyz requested review of this revision.
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Before this change, AAResults::getModRefInfo() was missing a case for
callbr instructions (asm goto), which may read/write memory. In PR52735,
this led to a miscompile where a load was incorrect eliminated.

Add this missing case, as well as an assert verifying that all
memory-accessing instructions are handled properly.

Fixes PR52735.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D115992

Files:
  llvm/lib/Analysis/AliasAnalysis.cpp
  llvm/test/Analysis/BasicAA/pr52735.ll


Index: llvm/test/Analysis/BasicAA/pr52735.ll
===================================================================
--- /dev/null
+++ llvm/test/Analysis/BasicAA/pr52735.ll
@@ -0,0 +1,29 @@
+; RUN: opt %s -basic-aa -aa-eval -print-all-alias-modref-info -disable-output 2>&1 | FileCheck %s
+;
+; Generated from:
+;
+; int foo() {
+;   int v;
+;   asm goto("movl $1, %0" : "=m"(v)::: out);
+; out:
+;   return v;
+; }
+
+target triple = "x86_64-unknown-linux-gnu"
+
+; CHECK-DAG: MayAlias: i32* %v, void (i32*, i8*)* asm "movl $$1, $0", "=*m,X,~{dirflag},~{fpsr},~{flags}"
+
+define dso_local i32 @foo() {
+entry:
+  %v = alloca i32, align 4
+  %0 = bitcast i32* %v to i8*
+  callbr void asm "movl $$1, $0", "=*m,X,~{dirflag},~{fpsr},~{flags}"(i32* nonnull %v, i8* blockaddress(@foo, %out))
+          to label %asm.fallthrough [label %out]
+
+asm.fallthrough:
+  br label %out
+
+out:
+  %1 = load i32, i32* %v, align 4
+  ret i32 %1
+}
Index: llvm/lib/Analysis/AliasAnalysis.cpp
===================================================================
--- llvm/lib/Analysis/AliasAnalysis.cpp
+++ llvm/lib/Analysis/AliasAnalysis.cpp
@@ -697,6 +697,8 @@
     return getModRefInfo((const AtomicRMWInst *)I, Loc, AAQIP);
   case Instruction::Call:
     return getModRefInfo((const CallInst *)I, Loc, AAQIP);
+  case Instruction::CallBr:
+    return getModRefInfo((const CallBrInst *)I, Loc, AAQIP);
   case Instruction::Invoke:
     return getModRefInfo((const InvokeInst *)I, Loc, AAQIP);
   case Instruction::CatchPad:
@@ -704,6 +706,8 @@
   case Instruction::CatchRet:
     return getModRefInfo((const CatchReturnInst *)I, Loc, AAQIP);
   default:
+    assert(!I->mayReadOrWriteMemory() &&
+           "Unhandled memory access instruction!");
     return ModRefInfo::NoModRef;
   }
 }


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