[llvm] r175553 - Fix a bug in mayHaveSideEffects. Functions that do not return are now considered as instructions with side effects.

[Nadav Rotem]

Author: nadav
Date: Tue Feb 19 14:02:09 2013
New Revision: 175553

URL: http://llvm.org/viewvc/llvm-project?rev=175553&view=rev
Log:

Fix a bug in mayHaveSideEffects. Functions that do not return are now considered as instructions with side effects. 

rdar://13227456


Added:
    llvm/trunk/test/Transforms/FunctionAttrs/noreturn.ll
Modified:
    llvm/trunk/include/llvm/IR/Instruction.h
    llvm/trunk/lib/IR/Instruction.cpp

Modified: llvm/trunk/include/llvm/IR/Instruction.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/IR/Instruction.h?rev=175553&r1=175552&r2=175553&view=diff
==============================================================================
--- llvm/trunk/include/llvm/IR/Instruction.h (original)
+++ llvm/trunk/include/llvm/IR/Instruction.h Tue Feb 19 14:02:09 2013
@@ -309,6 +309,12 @@ public:
   ///
   bool mayThrow() const;
 
+  /// mayReturn - Return true if this is a function that may return.
+  /// this is true for all normal instructions. The only exception
+  /// is functions that are marked with the 'noreturn' attribute.
+  ///
+  bool mayReturn() const;
+
   /// mayHaveSideEffects - Return true if the instruction may have side effects.
   ///
   /// Note that this does not consider malloc and alloca to have side
@@ -316,7 +322,7 @@ public:
   /// instructions which don't used the returned value.  For cases where this
   /// matters, isSafeToSpeculativelyExecute may be more appropriate.
   bool mayHaveSideEffects() const {
-    return mayWriteToMemory() || mayThrow();
+    return mayWriteToMemory() || mayThrow() || !mayReturn();
   }
 
   /// clone() - Create a copy of 'this' instruction that is identical in all

Modified: llvm/trunk/lib/IR/Instruction.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/IR/Instruction.cpp?rev=175553&r1=175552&r2=175553&view=diff
==============================================================================
--- llvm/trunk/lib/IR/Instruction.cpp (original)
+++ llvm/trunk/lib/IR/Instruction.cpp Tue Feb 19 14:02:09 2013
@@ -455,14 +455,18 @@ bool Instruction::mayWriteToMemory() con
   }
 }
 
-/// mayThrow - Return true if this instruction may throw an exception.
-///
 bool Instruction::mayThrow() const {
   if (const CallInst *CI = dyn_cast<CallInst>(this))
     return !CI->doesNotThrow();
   return isa<ResumeInst>(this);
 }
 
+bool Instruction::mayReturn() const {
+  if (const CallInst *CI = dyn_cast<CallInst>(this))
+    return !CI->doesNotReturn();
+  return true;
+}
+
 /// isAssociative - Return true if the instruction is associative:
 ///
 ///   Associative operators satisfy:  x op (y op z) === (x op y) op z

Added: llvm/trunk/test/Transforms/FunctionAttrs/noreturn.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/FunctionAttrs/noreturn.ll?rev=175553&view=auto
==============================================================================
--- llvm/trunk/test/Transforms/FunctionAttrs/noreturn.ll (added)
+++ llvm/trunk/test/Transforms/FunctionAttrs/noreturn.ll Tue Feb 19 14:02:09 2013
@@ -0,0 +1,18 @@
+; RUN: opt < %s -functionattrs -instcombine -S | FileCheck %s
+
+define void @endless_loop() noreturn nounwind readnone ssp uwtable {
+entry:
+  br label %while.body
+
+while.body:
+  br label %while.body
+}
+;CHECK: @main
+;CHECK: endless_loop
+;CHECK: ret
+define i32 @main() noreturn nounwind ssp uwtable {
+entry:
+  tail call void @endless_loop()
+  unreachable
+}
+