From 1b12d8855d8e84c37aeba8c99883e5ada6b5fdca Mon Sep 17 00:00:00 2001
From: Chris Lattner <sabre@nondot.org>
Date: Wed, 14 Nov 2007 06:19:25 +0000
Subject: [PATCH] Implement PR1796 and Transforms/SimplifyCFG/noreturn-call.ll
 by inserting unreachable after no-return calls.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@44099 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Transforms/Scalar/SimplifyCFG.cpp        | 74 ++++++++++++++++----
 test/Transforms/SimplifyCFG/noreturn-call.ll | 11 +++
 2 files changed, 70 insertions(+), 15 deletions(-)
 create mode 100644 test/Transforms/SimplifyCFG/noreturn-call.ll

diff --git a/lib/Transforms/Scalar/SimplifyCFG.cpp b/lib/Transforms/Scalar/SimplifyCFG.cpp
index 200264e9174..74005757206 100644
--- a/lib/Transforms/Scalar/SimplifyCFG.cpp
+++ b/lib/Transforms/Scalar/SimplifyCFG.cpp
@@ -24,6 +24,7 @@
 #include "llvm/Constants.h"
 #include "llvm/Instructions.h"
 #include "llvm/Module.h"
+#include "llvm/ParameterAttributes.h"
 #include "llvm/Support/CFG.h"
 #include "llvm/Support/Compiler.h"
 #include "llvm/Pass.h"
@@ -50,6 +51,46 @@ FunctionPass *llvm::createCFGSimplificationPass() {
   return new CFGSimplifyPass();
 }
 
+/// ChangeToUnreachable - Insert an unreachable instruction before the specified
+/// instruction, making it and the rest of the code in the block dead.
+static void ChangeToUnreachable(Instruction *I) {
+  BasicBlock *BB = I->getParent();
+  // Loop over all of the successors, removing BB's entry from any PHI
+  // nodes.
+  for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB); SI != SE; ++SI)
+    (*SI)->removePredecessor(BB);
+  
+  new UnreachableInst(I);
+  
+  // All instructions after this are dead.
+  BasicBlock::iterator BBI = I, BBE = BB->end();
+  while (BBI != BBE) {
+    if (!BBI->use_empty())
+      BBI->replaceAllUsesWith(UndefValue::get(BBI->getType()));
+    BB->getInstList().erase(BBI++);
+  }
+}
+
+/// IsNoReturn - Return true if the specified call is to a no-return function.
+static bool IsNoReturn(const CallInst *CI) {
+  if (const ParamAttrsList *Attrs = CI->getParamAttrs())
+    if (Attrs->paramHasAttr(0, ParamAttr::NoReturn))
+      return true;
+  
+  if (const Function *Callee = CI->getCalledFunction()) {
+    if (const ParamAttrsList *Attrs = Callee->getParamAttrs())
+      if (Attrs->paramHasAttr(0, ParamAttr::NoReturn))
+        return true;
+  
+    const FunctionType *FT = Callee->getFunctionType();
+    if (const ParamAttrsList *Attrs = FT->getParamAttrs())
+      if (Attrs->paramHasAttr(0, ParamAttr::NoReturn))
+        return true;
+  }
+  return false;
+}
+
+
 static bool MarkAliveBlocks(BasicBlock *BB,
                             SmallPtrSet<BasicBlock*, 128> &Reachable) {
   
@@ -66,26 +107,29 @@ static bool MarkAliveBlocks(BasicBlock *BB,
     // Do a quick scan of the basic block, turning any obviously unreachable
     // instructions into LLVM unreachable insts.  The instruction combining pass
     // canonnicalizes unreachable insts into stores to null or undef.
-    for (BasicBlock::iterator BBI = BB->begin(), E = BB->end(); BBI != E; ++BBI)
+    for (BasicBlock::iterator BBI = BB->begin(), E = BB->end(); BBI != E;++BBI){
+      if (CallInst *CI = dyn_cast<CallInst>(BBI)) {
+        if (IsNoReturn(CI)) {
+          // If we found a call to a no-return function, insert an unreachable
+          // instruction after it.  Make sure there isn't *already* one there
+          // though.
+          ++BBI;
+          if (!isa<UnreachableInst>(BBI)) {
+            ChangeToUnreachable(BBI);
+            Changed = true;
+          }
+          break;
+        }
+      }
+      
       if (StoreInst *SI = dyn_cast<StoreInst>(BBI))
         if (isa<ConstantPointerNull>(SI->getOperand(1)) ||
             isa<UndefValue>(SI->getOperand(1))) {
-          // Loop over all of the successors, removing BB's entry from any PHI
-          // nodes.
-          for (succ_iterator I = succ_begin(BB), SE = succ_end(BB); I != SE;++I)
-            (*I)->removePredecessor(BB);
-
-          new UnreachableInst(SI);
-
-          // All instructions after this are dead.
-          while (BBI != E) {
-            if (!BBI->use_empty())
-              BBI->replaceAllUsesWith(UndefValue::get(BBI->getType()));
-            BB->getInstList().erase(BBI++);
-          }
+          ChangeToUnreachable(SI);
+          Changed = true;
           break;
         }
-
+    }
 
     Changed |= ConstantFoldTerminator(BB);
     for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB); SI != SE; ++SI)
diff --git a/test/Transforms/SimplifyCFG/noreturn-call.ll b/test/Transforms/SimplifyCFG/noreturn-call.ll
new file mode 100644
index 00000000000..0e1c6327e8b
--- /dev/null
+++ b/test/Transforms/SimplifyCFG/noreturn-call.ll
@@ -0,0 +1,11 @@
+; RUN: llvm-as < %s | opt -simplifycfg | llvm-dis | grep unreachable
+; PR1796
+
+declare void @Finisher(i32) noreturn
+
+define void @YYY(i32) {
+  tail call void @Finisher(i32 %0) noreturn
+  tail call void @Finisher(i32 %0) noreturn
+  ret void
+}
+
-- 
2.34.1