CodeGen: Don't follow aliases when extracting type info.

[pcc]

Summary

This fixes a crash in the case where the type info object is an alias
pointing to a non-zero offset within a global or is otherwise unanalyzable
by the stripPointerCasts() function. Looking through the alias is not the
right thing to do anyway for similar reasons as D65118.

[pcc]

Ping.

[tejohnson]

LGTM with suggestion below.

llvm/test/CodeGen/X86/typeid-alias.ll

1 ↗

(On Diff #211868)

Add comment about what this is testing. Especially since nothing in the output is being checked (should it?).

[pcc]

llvm/test/CodeGen/X86/typeid-alias.ll

1 ↗

(On Diff #211868)

Done and added a basic sanity check that the output is valid.

llvm/trunk/lib/CodeGen/Analysis.cpp

void llvm::computeValueLLTs(const DataLayout &DL, Type &Ty,
   // Base case: we can get an LLT for this LLVM IR type.
   ValueTys.push_back(getLLTForType(Ty, DL));
   if (Offsets != nullptr)
     Offsets->push_back(StartingOffset * 8);
 }
 
 /// ExtractTypeInfo - Returns the type info, possibly bitcast, encoded in V.
 GlobalValue *llvm::ExtractTypeInfo(Value *V) {
-  V = V->stripPointerCasts();
+  V = V->stripPointerCastsNoFollowAliases();
   GlobalValue *GV = dyn_cast<GlobalValue>(V);
   GlobalVariable *Var = dyn_cast<GlobalVariable>(V);
 
   if (Var && Var->getName() == "llvm.eh.catch.all.value") {
     assert(Var->hasInitializer() &&
            "The EH catch-all value must have an initializer");
     Value *Init = Var->getInitializer();
     GV = dyn_cast<GlobalValue>(Init);

llvm/trunk/test/CodeGen/X86/typeid-alias.ll

+; Test that we don't crash in the case where the type info object is an
+; alias pointing to a non-zero offset within a global.
+
+; RUN: llc < %s | FileCheck %s
+
+target triple = "x86_64-unknown-linux-gnu"
+
+%struct.exception = type { i8, i8, i32, i8*, i8*, i32, i8* }
+@g = global %struct.exception zeroinitializer
+@a = alias %struct.exception, %struct.exception* inttoptr (i64 add (i64 ptrtoint (%struct.exception* @g to i64), i64 1297036692682702848) to %struct.exception*)
+
+define i32 @typeid() {
+  ; CHECK: movl $1, %eax
+  %eh_typeid = tail call i32 @llvm.eh.typeid.for( i8* getelementptr (%struct.exception, %struct.exception* @a, i32 0, i32 0))
+  ret i32 %eh_typeid
+}
+
+declare i32 @llvm.eh.typeid.for(i8*)