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9276050d30
llvm/lib/IR
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George Burgess IV 9276050d30 [LoopVectorize] Don't preserve nsw/nuw flags on shrunken ops. 
If we're shrinking a binary operation, it may be the case that the new
operations wraps where the old didn't. If this happens, the behavior
should be well-defined. So, we can't always carry wrapping flags with us
when we shrink operations.

If we do, we get incorrect optimizations in cases like:

void foo(const unsigned char *from, unsigned char *to, int n) {
  for (int i = 0; i < n; i++)
    to[i] = from[i] - 128;
}

which gets optimized to:

void foo(const unsigned char *from, unsigned char *to, int n) {
  for (int i = 0; i < n; i++)
    to[i] = from[i] | 128;
}

Because:
- InstCombine turned `sub i32 %from.i, 128` into
  `add nuw nsw i32 %from.i, 128`.
- LoopVectorize vectorized the add to be `add nuw nsw <16 x i8>` with a
  vector full of `i8 128`s
- InstCombine took advantage of the fact that the newly-shrunken add
  "couldn't wrap", and changed the `add` to an `or`.

InstCombine seems happy to figure out whether we can add nuw/nsw on its
own, so I just decided to drop the flags. There are already a number of
places in LoopVectorize where we rely on InstCombine to clean up.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@305053 91177308-0d34-0410-b5e6-96231b3b80d8
2017-06-09 03:56:15 +00:00
..
AsmWriter.cpp Move Object format code to lib/BinaryFormat. 2017-06-07 03:48:56 +00:00
AttributeImpl.h [IR] Switch AttributeList to use an array for O(1) access 2017-05-23 17:01:48 +00:00
Attributes.cpp Sort the remaining #include lines in include/... and lib/.... 2017-06-06 11:49:48 +00:00
AttributesCompatFunc.td Provide a way to specify inliner's attribute compatibility and merging. 2015-12-22 23:57:37 +00:00
AutoUpgrade.cpp Added missing break. 2017-05-19 20:31:51 +00:00
BasicBlock.cpp [IR] Add an iterator and range accessor for the PHI nodes of a basic 2017-05-26 03:10:00 +00:00
CMakeLists.txt [CMake] NFC. Updating CMake dependency specifications 2016-11-17 04:36:50 +00:00
Comdat.cpp Sort the remaining #include lines in include/... and lib/.... 2017-06-06 11:49:48 +00:00
ConstantFold.cpp ConstantFold: Handle gep nonnull, undef as well 2017-05-08 17:37:33 +00:00
ConstantFold.h IR: Introduce inrange attribute on getelementptr indices. 2016-11-10 22:34:55 +00:00
ConstantRange.cpp Sort the remaining #include lines in include/... and lib/.... 2017-06-06 11:49:48 +00:00
Constants.cpp [Constants] Use isUIntN/isIntN from MathExtras instead of reimplementing the same code. NFC 2017-06-07 00:58:05 +00:00
ConstantsContext.h [IR] De-virtualize ~Value to save a vptr 2017-05-18 17:24:10 +00:00
Core.cpp [LLVM-C] [OCaml] Expose Type::subtypes. 2017-06-05 11:49:52 +00:00
DataLayout.cpp Sort the remaining #include lines in include/... and lib/.... 2017-06-06 11:49:48 +00:00
DebugInfo.cpp Sort the remaining #include lines in include/... and lib/.... 2017-06-06 11:49:48 +00:00
DebugInfoMetadata.cpp [codeview] Check for a DIExpression offset for local variables 2017-05-09 19:59:29 +00:00
DebugLoc.cpp Sort the remaining #include lines in include/... and lib/.... 2017-06-06 11:49:48 +00:00
DiagnosticInfo.cpp Sort the remaining #include lines in include/... and lib/.... 2017-06-06 11:49:48 +00:00
DiagnosticPrinter.cpp Sort the remaining #include lines in include/... and lib/.... 2017-06-06 11:49:48 +00:00
DIBuilder.cpp Move Object format code to lib/BinaryFormat. 2017-06-07 03:48:56 +00:00
Dominators.cpp Handle non-unique edges in edge-dominance 2017-06-05 16:27:09 +00:00
Function.cpp Sort the remaining #include lines in include/... and lib/.... 2017-06-06 11:49:48 +00:00
GCOV.cpp [gcov] Sort file info before printing it 2017-04-26 00:16:10 +00:00
Globals.cpp Sort the remaining #include lines in include/... and lib/.... 2017-06-06 11:49:48 +00:00
GVMaterializer.cpp [Layering] Move GVMaterializer.h into the IR library where its 2014-03-06 03:50:29 +00:00
InlineAsm.cpp Sort the remaining #include lines in include/... and lib/.... 2017-06-06 11:49:48 +00:00
Instruction.cpp [LoopVectorize] Don't preserve nsw/nuw flags on shrunken ops. 2017-06-09 03:56:15 +00:00
Instructions.cpp [IR] Remove getNumSuccessorsV/getSuccessorV/setSuccessorV from the TerminatorInst subclasses as much as possible now that Value has been de-virtualized 2017-06-08 23:23:08 +00:00
IntrinsicInst.cpp Sort the remaining #include lines in include/... and lib/.... 2017-06-06 11:49:48 +00:00
IRBuilder.cpp [Atomics][LoopIdiom] Recognize unordered atomic memcpy 2017-06-06 16:45:25 +00:00
IRPrintingPasses.cpp Implement getPassName() for IR printing passes. 2017-03-10 07:09:20 +00:00
LegacyPassManager.cpp [llvm] Remove double semicolons 2017-06-06 05:08:36 +00:00
LLVMBuild.txt Move Object format code to lib/BinaryFormat. 2017-06-07 03:48:56 +00:00
LLVMContext.cpp Sort the remaining #include lines in include/... and lib/.... 2017-06-06 11:49:48 +00:00
LLVMContextImpl.cpp [IR] De-virtualize ~Value to save a vptr 2017-05-18 17:24:10 +00:00
LLVMContextImpl.h Move Object format code to lib/BinaryFormat. 2017-06-07 03:48:56 +00:00
Mangler.cpp Move llvm::emitLinkerFlagsForGlobalCOFF() to Mangler. 2017-03-31 04:46:50 +00:00
MDBuilder.cpp Add function importing info from samplepgo profile to the module summary. 2017-02-28 18:09:44 +00:00
Metadata.cpp Sort the remaining #include lines in include/... and lib/.... 2017-06-06 11:49:48 +00:00
MetadataImpl.h DI: Disallow uniquable DICompileUnits 2015-08-03 17:26:41 +00:00
Module.cpp Sort the remaining #include lines in include/... and lib/.... 2017-06-06 11:49:48 +00:00
ModuleSummaryIndex.cpp Re-apply r302108, "IR: Use pointers instead of GUIDs to represent edges in the module summary. NFCI." 2017-05-04 18:03:25 +00:00
Operator.cpp [IR] Remove some unneeded includes from Operator.h and fix cpp files that were transitively depending on it. NFC 2017-03-20 05:08:41 +00:00
OptBisect.cpp Sort the remaining #include lines in include/... and lib/.... 2017-06-06 11:49:48 +00:00
Pass.cpp Cleanup dump() functions. 2017-01-28 02:02:38 +00:00
PassManager.cpp [PM] Introduce an analysis set used to preserve all analyses over 2017-01-15 06:32:49 +00:00
PassRegistry.cpp [LegacyPassManager] Remove TargetMachine constructors 2017-05-18 17:21:13 +00:00
ProfileSummary.cpp Reapply r271728 after adding move cobstructor for ProfileSummaryInfo 2016-06-03 22:54:26 +00:00
Statepoint.cpp Rename AttributeSet to AttributeList 2017-03-21 16:57:19 +00:00
SymbolTableListTraitsImpl.h ADT: Remove external uses of ilist_iterator, NFC 2016-09-03 01:22:56 +00:00
Type.cpp Sort the remaining #include lines in include/... and lib/.... 2017-06-06 11:49:48 +00:00
TypeFinder.cpp Sort the remaining #include lines in include/... and lib/.... 2017-06-06 11:49:48 +00:00
Use.cpp Revert r240137 (Fixed/added namespace ending comments using clang-tidy. NFC) 2015-06-23 09:49:53 +00:00
User.cpp [IR] De-virtualize ~Value to save a vptr 2017-05-18 17:24:10 +00:00
Value.cpp [IR] De-virtualize ~Value to save a vptr 2017-05-18 17:24:10 +00:00
ValueSymbolTable.cpp Sort the remaining #include lines in include/... and lib/.... 2017-06-06 11:49:48 +00:00
ValueTypes.cpp [MVT] add v1i1 MVT 2017-05-18 11:29:41 +00:00
Verifier.cpp Move Object format code to lib/BinaryFormat. 2017-06-07 03:48:56 +00:00