[llvm] r273762 - The absence of noreturn doesn't ensure mayReturn
David Majnemer via llvm-commits
llvm-commits at lists.llvm.org
Fri Jun 24 17:55:12 PDT 2016
Author: majnemer
Date: Fri Jun 24 19:55:12 2016
New Revision: 273762
URL: http://llvm.org/viewvc/llvm-project?rev=273762&view=rev
Log:
The absence of noreturn doesn't ensure mayReturn
There are two separate issues:
- LLVM doesn't consider infinite loops to be side effects: we happily
hoist/sink above/below loops whose bounds are unknown.
- The absence of the noreturn attribute is insufficient for us to know
if a function will definitely return. Relying on noreturn in the
middle-end for any property is an accident waiting to happen.
Removed:
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=273762&r1=273761&r2=273762&view=diff
==============================================================================
--- llvm/trunk/include/llvm/IR/Instruction.h (original)
+++ llvm/trunk/include/llvm/IR/Instruction.h Fri Jun 24 19:55:12 2016
@@ -394,21 +394,13 @@ public:
/// Return true if this instruction may throw an exception.
bool mayThrow() const;
- /// 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;
-
/// Return true if the instruction may have side effects.
///
/// Note that this does not consider malloc and alloca to have side
/// effects because the newly allocated memory is completely invisible to
/// instructions which don't use the returned value. For cases where this
/// matters, isSafeToSpeculativelyExecute may be more appropriate.
- bool mayHaveSideEffects() const {
- return mayWriteToMemory() || mayThrow() || !mayReturn();
- }
+ bool mayHaveSideEffects() const { return mayWriteToMemory() || mayThrow(); }
/// Return true if the instruction is a variety of EH-block.
bool isEHPad() const {
Modified: llvm/trunk/lib/IR/Instruction.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/IR/Instruction.cpp?rev=273762&r1=273761&r2=273762&view=diff
==============================================================================
--- llvm/trunk/lib/IR/Instruction.cpp (original)
+++ llvm/trunk/lib/IR/Instruction.cpp Fri Jun 24 19:55:12 2016
@@ -545,12 +545,6 @@ bool Instruction::mayThrow() const {
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
Removed: llvm/trunk/test/Transforms/FunctionAttrs/noreturn.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/FunctionAttrs/noreturn.ll?rev=273761&view=auto
==============================================================================
--- llvm/trunk/test/Transforms/FunctionAttrs/noreturn.ll (original)
+++ llvm/trunk/test/Transforms/FunctionAttrs/noreturn.ll (removed)
@@ -1,18 +0,0 @@
-; 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-LABEL: @main(
-;CHECK: endless_loop
-;CHECK: ret
-define i32 @main() noreturn nounwind ssp uwtable {
-entry:
- tail call void @endless_loop()
- unreachable
-}
-
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