Change the representation of GNU ?: expressions to use a different expression

class and to bind the shared value using OpaqueValueExpr.  This fixes an
unnoticed problem with deserialization of these expressions where the
deserialized form would lose the vital pointer-equality trait;  or rather,
it fixes it because this patch also does the right thing for deserializing
OVEs.

Change OVEs to not be a "temporary object" in the sense that copy elision is
permitted.

This new representation is not totally unawkward to work with, but I think
that's really part and parcel with the semantics we're modelling here.  In
particular, it's much easier to fix things like the copy elision bug and to
make the CFG look right.

I've tried to update the analyzer to deal with this in at least some          
obvious cases, and I think we get a much better CFG out, but the printing
of OpaqueValueExprs probably needs some work.

llvm-svn: 125744

1 files changed, 27 insertions, 0 deletions

diff --git a/clang/lib/CodeGen/CodeGenFunction.cpp b/clang/lib/CodeGen/CodeGenFunction.cpp
index b316fa86f1e..96716ad9ccf 100644
--- a/clang/lib/CodeGen/CodeGenFunction.cpp
+++ b/clang/lib/CodeGen/CodeGenFunction.cpp
@@ -762,3 +762,30 @@ void CodeGenFunction::EmitDeclRefExprDbgValue(const DeclRefExpr *E,
   if (CGDebugInfo *Dbg = getDebugInfo())
     Dbg->EmitGlobalVariable(E->getDecl(), Init);
 }
+
+CodeGenFunction::PeepholeProtection
+CodeGenFunction::protectFromPeepholes(RValue rvalue) {
+  // At the moment, the only aggressive peephole we do in IR gen
+  // is trunc(zext) folding, but if we add more, we can easily
+  // extend this protection.
+
+  if (!rvalue.isScalar()) return PeepholeProtection();
+  llvm::Value *value = rvalue.getScalarVal();
+  if (!isa<llvm::ZExtInst>(value)) return PeepholeProtection();
+
+  // Just make an extra bitcast.
+  assert(HaveInsertPoint());
+  llvm::Instruction *inst = new llvm::BitCastInst(value, value->getType(), "",
+                                                  Builder.GetInsertBlock());
+
+  PeepholeProtection protection;
+  protection.Inst = inst;
+  return protection;
+}
+
+void CodeGenFunction::unprotectFromPeepholes(PeepholeProtection protection) {
+  if (!protection.Inst) return;
+
+  // In theory, we could try to duplicate the peepholes now, but whatever.
+  protection.Inst->eraseFromParent();
+}