SimplifyAllocas: search through more bitcasts to find alloca for llvm.dbg.declare.

lib/Transforms/NaCl/SimplifyAllocas.cpp

Index: lib/Transforms/NaCl/SimplifyAllocas.cpp
diff --git a/lib/Transforms/NaCl/SimplifyAllocas.cpp b/lib/Transforms/NaCl/SimplifyAllocas.cpp
index ba25b5f961ad5ca28254e67de200b003bb2558e8..4ede8b5704f6b8dcb4f18035b3cae82dd42d150b 100644
--- a/lib/Transforms/NaCl/SimplifyAllocas.cpp
+++ b/lib/Transforms/NaCl/SimplifyAllocas.cpp
@@ -18,7 +18,9 @@
 #include "llvm/IR/IntrinsicInst.h"
 #include "llvm/IR/Module.h"
 #include "llvm/Transforms/NaCl.h"
+#include "llvm/Support/Debug.h"
 #include "llvm/Support/raw_ostream.h"
+
 using namespace llvm;
 namespace {
 class SimplifyAllocas : public BasicBlockPass {
@@ -50,6 +52,21 @@ private:
     return false;
   }
 
+  AllocaInst *findAllocaFromBC(BitCastInst *BCInst) {
+    Value *Op0 = BCInst->getOperand(0);
+    while (!llvm::isa<AllocaInst>(Op0)) {
+      if (auto *NextBC = llvm::dyn_cast<BitCastInst>(Op0)) {
+        Op0 = NextBC->getOperand(0);
+      } else {
+        dbgs() << "findAllocaFromBC encountered a non-bitcast intermediate val "
+               << *Op0 << " starting w/ BCInst " << *BCInst << "\n";
+        llvm_unreachable("failed to find alloca");
+        return nullptr;
+      }
+    }
+    return llvm::cast<AllocaInst>(Op0);
+  }
+
   bool runOnBasicBlock(BasicBlock &BB) override {
     bool Changed = false;
     for (BasicBlock::iterator I = BB.getFirstInsertionPt(), E = BB.end();
@@ -106,12 +123,11 @@ private:
           // Sometimes dbg.declare points to an argument instead of an alloca.
           if (auto *VM = dyn_cast<ValueAsMetadata>(MV->getMetadata())) {
             if (auto *BCInst = dyn_cast<BitCastInst>(VM->getValue())) {
-              Value *CastSrc = BCInst->getOperand(0);
-              assert(isa<AllocaInst>(CastSrc));
+              AllocaInst *Alloca = findAllocaFromBC(BCInst);
               Call->setArgOperand(
                   0,
                   MetadataAsValue::get(Inst->getContext(),
-                                       ValueAsMetadata::get(CastSrc)));
+                                       ValueAsMetadata::get(Alloca)));

[Derek Schuff, 2015/06/11 17:43:12]

what will ValueAsMetadata do if you call get on nullptr?

[jvoung (off chromium), 2015/06/11 17:52:19]

It'll assert or deref null. I'll change the findAllocaFromBC to
report_fatal_error instead of returning nullptr?

               Changed = true;
             }
           }