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author | Duncan P. N. Exon Smith <dexonsmith@apple.com> | 2014-06-12 21:16:19 +0000 |
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committer | Duncan P. N. Exon Smith <dexonsmith@apple.com> | 2014-06-12 21:16:19 +0000 |
commit | 3fdfffbfa344858ce0ffb3dec9a997fb40584857 (patch) | |
tree | 437cb411e972aa1dce985c25f404f8255b5e3ed6 /lib | |
parent | 00c3986254430289472ad839c86dae252139b89c (diff) | |
download | llvm-3fdfffbfa344858ce0ffb3dec9a997fb40584857.tar.gz llvm-3fdfffbfa344858ce0ffb3dec9a997fb40584857.tar.bz2 llvm-3fdfffbfa344858ce0ffb3dec9a997fb40584857.tar.xz |
GVN: Enable value forwarding for calloc
Enable value forwarding for loads from `calloc()` without an intervening
store.
This change extends GVN to handle the following case:
%1 = tail call noalias i8* @calloc(i64 1, i64 4)
%2 = bitcast i8* %1 to i32*
; This load is trivially constant zero
%3 = load i32* %2, align 4
This is analogous to the handling for `malloc()` in the same places.
`malloc()` returns `undef`; `calloc()` returns a zero value. Note that
it is correct to return zero even for out of bounds GEPs since the
result of such a GEP would be undefined.
Patch by Philip Reames!
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@210828 91177308-0d34-0410-b5e6-96231b3b80d8
Diffstat (limited to 'lib')
-rw-r--r-- | lib/Transforms/Scalar/GVN.cpp | 16 |
1 files changed, 16 insertions, 0 deletions
diff --git a/lib/Transforms/Scalar/GVN.cpp b/lib/Transforms/Scalar/GVN.cpp index 6d07dddd3e..56781d44aa 100644 --- a/lib/Transforms/Scalar/GVN.cpp +++ b/lib/Transforms/Scalar/GVN.cpp @@ -1464,6 +1464,13 @@ void GVN::AnalyzeLoadAvailability(LoadInst *LI, LoadDepVect &Deps, continue; } + // Loading from calloc (which zero initializes memory) -> zero + if (isCallocLikeFn(DepInst, TLI)) { + ValuesPerBlock.push_back(AvailableValueInBlock::get( + DepBB, Constant::getNullValue(LI->getType()))); + continue; + } + if (StoreInst *S = dyn_cast<StoreInst>(DepInst)) { // Reject loads and stores that are to the same address but are of // different types if we have to. @@ -1988,6 +1995,15 @@ bool GVN::processLoad(LoadInst *L) { } } + // If this load follows a calloc (which zero initializes memory), + // then the loaded value is zero + if (isCallocLikeFn(DepInst, TLI)) { + L->replaceAllUsesWith(Constant::getNullValue(L->getType())); + markInstructionForDeletion(L); + ++NumGVNLoad; + return true; + } + return false; } |