Subzero: Validate phi instructions after CFG construction.
It checks that each phi label corresponds to an incoming edge, and that each incoming edge has a corresponding phi label.
It does not check that duplicate incoming edges get the same phi value.
Performance impact is minimal (~0.2%) despite the O(N^2) implementation.
BUG= https://code.google.com/p/nativeclient/issues/detail?id=4304
R=jpp@chromium.org
Review URL: https://codereview.chromium.org/1351433002 .
diff --git a/src/IceCfgNode.cpp b/src/IceCfgNode.cpp
index cb8d97e..0ccc6ea 100644
--- a/src/IceCfgNode.cpp
+++ b/src/IceCfgNode.cpp
@@ -80,6 +80,46 @@
OutEdges = Insts.rbegin()->getTerminatorEdges();
}
+// Validate each Phi instruction in the node with respect to control flow. For
+// every phi argument, its label must appear in the predecessor list. For each
+// predecessor, there must be a phi argument with that label. We don't check
+// that phi arguments with the same label have the same value.
+void CfgNode::validatePhis() {
+ for (Inst &Instr : Phis) {
+ auto *Phi = llvm::cast<InstPhi>(&Instr);
+ // We do a simple O(N^2) algorithm to check for consistency. Even so, it
+ // shows up as only about 0.2% of the total translation time. But if
+ // necessary, we could improve the complexity by using a hash table to count
+ // how many times each node is referenced in the Phi instruction, and how
+ // many times each node is referenced in the incoming edge list, and compare
+ // the two for equality.
+ for (SizeT i = 0; i < Phi->getSrcSize(); ++i) {
+ CfgNode *Label = Phi->getLabel(i);
+ bool Found = false;
+ for (CfgNode *InNode : getInEdges()) {
+ if (InNode == Label) {
+ Found = true;
+ break;
+ }
+ }
+ if (!Found)
+ llvm::report_fatal_error("Phi error: label for bad incoming edge");
+ }
+ for (CfgNode *InNode : getInEdges()) {
+ bool Found = false;
+ for (SizeT i = 0; i < Phi->getSrcSize(); ++i) {
+ CfgNode *Label = Phi->getLabel(i);
+ if (InNode == Label) {
+ Found = true;
+ break;
+ }
+ }
+ if (!Found)
+ llvm::report_fatal_error("Phi error: missing label for incoming edge");
+ }
+ }
+}
+
// This does part 1 of Phi lowering, by creating a new dest variable
// for each Phi instruction, replacing the Phi instruction's dest with
// that variable, and adding an explicit assignment of the old dest to
