Comments (6)
wsmoses
commented on May 27, 2024
I've reproduced this and deduced that we weren't enabling scoped alias analysis (and thus Enzyme, without that improved alias info, had to assume extra things cached). Happily turning that on eliminates the caches completely (which is undergoing a PR now).
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unrealwill
commented on May 27, 2024
Thanks for the quick fix ! 👍
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unrealwill
commented on May 27, 2024
FYI, I cloned a fresh enzyme revision 6117bbd which should contain the current fix, then rebuild, and reinstall Enzyme.
But I still observe the bug with clang version 11.1.0
I'll try a more recent clang (hopefully it will have a compatible Cuda version).
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unrealwill
commented on May 27, 2024
The bug is also present with
clang version 12.0.1 freshly installed from https://github.com/llvm/llvm-project/tree/release/12.x
I'll try clang's mainline
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wsmoses
commented on May 27, 2024
Just to confirm, can you past the output of the analysis?
Specifically, the thing to look for is that there's no more lines like bugDense.cpp:21:31: remark: Caching instruction
There will still exist some lines like bugDense.cpp:21:21: remark: Load may need caching which effectively say that you're overwriting out and if you need the old value of out, it needs to be cached because of this store. A different analysis (differential use analysis) will determine that Enzyme won't need the old value of out in the reverse, and thus there's no need to cache it (and thus no Caching instruction...)
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unrealwill
commented on May 27, 2024
OK, it still spits plenty of lines but looking more carefully there is no longer "remark: Caching instruction".
👍 so I guess it should be OK now.
There is still a "remark: Load must be recomputed" though (but I care less about this provided it's not quadratic)
Here is the new output :
clang bugDense.cpp -lstdc++ -lm -fno-exceptions -Rpass=enzyme -Xclang -load -Xclang /usr/local/lib/ClangEnzyme-12.so -O2 -o bin/bugDense
remark: Load may need caching %arrayidx9.promoted.i = load double, double* %arrayidx9.i, align 8, !tbaa !47, !alias.scope !32, !noalias !44 due to store double %add10.i, double* %arrayidx9.i, align 8, !dbg !49, !tbaa !47, !alias.scope !32, !noalias !44 [-Rpass=enzyme]
bugDense.cpp:21:21: remark: Load may need caching %10 = load double, double* %arrayidx.i, align 8, !dbg !56, !tbaa !47, !alias.scope !26, !noalias !57 due to tail call void @llvm.memset.p0i8.i64(i8* align 8 %v6.i.i34, i8 0, i64 %15, i1 false) #12, !dbg !79, !alias.scope !80, !noalias !83 [-Rpass=enzyme]
out[i] += A[i*m+j] *x[j];
^
bugDense.cpp:21:31: remark: Load may need caching %11 = load double, double* %arrayidx6.i, align 8, !dbg !58, !tbaa !47, !alias.scope !30, !noalias !59 due to tail call void @llvm.memset.p0i8.i64(i8* align 8 %v6.i.i34, i8 0, i64 %15, i1 false) #12, !dbg !79, !alias.scope !80, !noalias !83 [-Rpass=enzyme]
out[i] += A[i*m+j] *x[j];
^
remark: Load may need caching %arrayidx9.promoted.i43 = load double, double* %arrayidx9.i42, align 8, !tbaa !47, !alias.scope !74, !noalias !83 due to store double %add10.i54, double* %arrayidx9.i42, align 8, !dbg !86, !tbaa !47, !alias.scope !74, !noalias !83 [-Rpass=enzyme]
bugDense.cpp:21:31: remark: Load must be recomputed %11 = load double, double* %arrayidx6.i, align 8, !dbg !58, !tbaa !47, !alias.scope !30, !noalias !59 in reverse_invertfor.body4.i due to tail call void @llvm.memset.p0i8.i64(i8* align 8 %v6.i.i34, i8 0, i64 %15, i1 false) #12, !dbg !79, !alias.scope !80, !noalias !83 [-Rpass=enzyme]
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