PNaCl: Fix ExpandTls to handle a couple of corner cases involving PHI nodes

ExpandTls's use of replaceUsesOfWith() didn't work for PHI nodes
containing the same Constant twice (which needs to work for same or
differing incoming BasicBlocks).  The same applies to
ExpandTlsConstantExpr.

I noticed this while implementing ExpandConstantExpr.

Fix this and factor out some common code that all three passes can
use.

BUG=https://code.google.com/p/nativeclient/issues/detail?id=2837
TEST=test/Transforms/NaCl/*.ll

Review URL: https://codereview.chromium.org/13128002

1 files changed, 40 insertions, 0 deletions

diff --git a/lib/Transforms/NaCl/ExpandUtils.cpp b/lib/Transforms/NaCl/ExpandUtils.cpp
new file mode 100644
index 0000000000..0670ff75ce
--- /dev/null
+++ b/lib/Transforms/NaCl/ExpandUtils.cpp
@@ -0,0 +1,40 @@
+//===-- ExpandUtils.cpp - Helper functions for expansion passes -----------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/IR/BasicBlock.h"
+#include "llvm/IR/Instructions.h"
+#include "llvm/Transforms/NaCl.h"
+
+using namespace llvm;
+
+Instruction *llvm::PhiSafeInsertPt(Use *U) {
+  Instruction *InsertPt = cast<Instruction>(U->getUser());
+  if (PHINode *PN = dyn_cast<PHINode>(InsertPt)) {
+    // We cannot insert instructions before a PHI node, so insert
+    // before the incoming block's terminator.  This could be
+    // suboptimal if the terminator is a conditional.
+    InsertPt = PN->getIncomingBlock(*U)->getTerminator();
+  }
+  return InsertPt;
+}
+
+void llvm::PhiSafeReplaceUses(Use *U, Value *NewVal) {
+  if (PHINode *PN = dyn_cast<PHINode>(U->getUser())) {
+    // A PHI node can have multiple incoming edges from the same
+    // block, in which case all these edges must have the same
+    // incoming value.
+    BasicBlock *BB = PN->getIncomingBlock(*U);
+    for (unsigned I = 0; I < PN->getNumIncomingValues(); ++I) {
+      if (PN->getIncomingBlock(I) == BB)
+        PN->setIncomingValue(I, NewVal);
+    }
+  } else {
+    U->getUser()->replaceUsesOfWith(U->get(), NewVal);
+  }
+}