[AA] Handle callbr instructions in alias analysis.

[rickyz]

Summary

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.

[nikic]

LGTM

llvm/lib/Analysis/AliasAnalysis.cpp

698–701

As an optional suggestion, I think this would make it clearer which overload gets actually called.

llvm/test/Analysis/BasicAA/pr52735.ll

15

Just CHECK suffices here.

[rickyz]

Respond to comments.

[rickyz]

Thanks for the review! I'm not a committer, so can you please commit this if it looks good?

[nikic]

In D115992#3201430, @rickyz wrote:

Thanks for the review! I'm not a committer, so can you please commit this if it looks good?

Sure, can you please share Your Name <your@email> to use for attribution?

[rickyz]

Sure thing:

Ricky Zhou <[e-mail]>

llvm/lib/Analysis/AliasAnalysis.cpp

ModRefInfo AAResults::getModRefInfo(const Instruction *I,
   case Instruction::Store:
     return getModRefInfo((const StoreInst *)I, Loc, AAQIP);
   case Instruction::Fence:
     return getModRefInfo((const FenceInst *)I, Loc, AAQIP);
   case Instruction::AtomicCmpXchg:
     return getModRefInfo((const AtomicCmpXchgInst *)I, Loc, AAQIP);
   case Instruction::AtomicRMW:
     return getModRefInfo((const AtomicRMWInst *)I, Loc, AAQIP);
   case Instruction::Call:
-    return getModRefInfo((const CallInst *)I, Loc, AAQIP);
+  case Instruction::CallBr:
   case Instruction::Invoke:
-    return getModRefInfo((const InvokeInst *)I, Loc, AAQIP);
+    return getModRefInfo((const CallBase *)I, Loc, AAQIP);
   case Instruction::CatchPad:
     return getModRefInfo((const CatchPadInst *)I, Loc, AAQIP);
   case Instruction::CatchRet:
     return getModRefInfo((const CatchReturnInst *)I, Loc, AAQIP);
   default:
+    assert(!I->mayReadOrWriteMemory() &&
+           "Unhandled memory access instruction!");
     return ModRefInfo::NoModRef;
   }
 }
 
 /// Return information about whether a particular call site modifies
 /// or reads the specified memory location \p MemLoc before instruction \p I
 /// in a BasicBlock.
 /// FIXME: this is really just shoring-up a deficiency in alias analysis.

llvm/test/Analysis/BasicAA/pr52735.ll

+; 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: 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
+}