Prior to this change LLVM would happily elide a call to any allocation
function and a call to any free function operating on the same unused
pointer. This can cause problems in some obscure cases, for example if
the body of operator::new can be inlined but the body of
operator::delete can't, as in this example from jyknight:
#include <stdlib.h>
#include <stdio.h>
int allocs = 0;
void *operator new(size_t n) {
allocs++;
void *mem = malloc(n);
if (!mem) abort();
return mem;
}
__attribute__((noinline)) void operator delete(void *mem) noexcept {
allocs--;
free(mem);
}
void deleteit(int*i) { delete i; }
int main() {
int*i = new int;
deleteit(i);
if (allocs != 0)
printf("MEMORY LEAK! allocs: %d\n", allocs);
}
This patch addresses the issue by introducing the concept of an
allocator function family and uses it to make sure that alloc/free
function pairs are only removed if they're in the same family.
Differential Revision: https://reviews.llvm.org/D117356
To make this actually trigger, we also need to check whether the
function types differ, which is a hidden cast under opaque pointers.
The transform is somewhat less relevant there because it is
primarily about pointer bitcasts, but it can also happen with other
bit- or pointer-castable types.
Byval handling is easier with opaque pointers because there is no
need to adjust the byval type, we only need to make sure that it's
still a pointer.
The logic for handling this was fixed in
8d7f118ab2, but the check for byval
on the callee was retained. This resulted in a weird situation
where the transform would work depending on whether the byval
was only on the call or on both the call and the function.
This is a recommit without changes. I originally reverted this
due to a significant code-size regression on tramp3d-v4, however
further investigation showed that in the tramp3d-v4 case this
change enables additional optimizations (in particular more
jump threading), which happens to reduce the size of a function
just enough to be eligible for inlining at hot callsites, which
results in the code size increase. As such, this was just bad
luck.
-----
This one-use limitation is artificial, we do not increase
instruction count if we perform the fold with multiple uses. The
motivating case is shown in @sub_eq_zero_select, where the one-use
limitation causes us to miss a subsequent select fold.
I believe the backend is pretty good about reusing flag-producing
subs for cmps with same operands, so I think doing this is fine.
Differential Revision: https://reviews.llvm.org/D120337
For conditional branches, we know the value is i1 0 or i1 1 along
the outgoing edges. For switches we can apply exactly the same
optimization, just with the known values determined by the switch
cases.
This transform can still be applied if there are more than two
phi inputs, as long as phi inputs with the same value are dominated
by the same idom edge.
Treat the icmp and sub symmetrically, and require that one of them
has one use, not the icmp in particular. This could be further
relaxed in the abs (but not nabs) case to not check one-use at
all.
extractvalue (any_mul_with_overflow X, -1), 0 --> -X
There are similar other potential transforms that we could do as
noted by the last TODO in the test diffs.
Fixes#54053
Now that we canonicalize SPF min/max to intrinsics, there's no
need to canonicalize the structure of the SPF min/max itself
anymore. This is conceptually NFC, but in practice does slightly
impact results due to folding order differences.
Now that integer min/max intrinsics have good support in both
InstCombine and other passes, start canonicalizing SPF min/max
to intrinsic min/max.
Once this sticks, we can stop matching SPF min/max in various
places, and can remove hacks we have for preventing infinite loops
and breaking of SPF canonicalization.
Differential Revision: https://reviews.llvm.org/D98152
What we're really doing here is converting Op0 udiv Op1 into
Op0 lshr log2(Op1), so phrase it in that way. Actually pushing
the lshr into the log2(Op1) expression should be seen as a separate
transform.
This is the same special logic we apply for SPF signed clamps
when computing the number of sign bits, just for intrinsics.
This just uses the same logic as the select case, but there's
multiple directions this could be improved in: We could also use
the num sign bits from the clamped value, we could do this during
constant range calculation, and there's probably unsigned analogues
for the constant range case at least.
This one-use limitation is artificial, we do not increase
instruction count if we perform the fold with multiple uses. The
motivating case is shown in @sub_eq_zero_select, where the one-use
limitation causes us to miss a subsequent select fold.
I believe the backend is pretty good about reusing flag-producing
subs for cmps with same operands, so I think doing this is fine.
Differential Revision: https://reviews.llvm.org/D120337
This patch fixes an invalid TypeSize->uint64_t implicit conversion in
FoldReinterpretLoadFromConst. If the size of the constant is scalable
we bail out of the optimisation for now.
Tests added here:
Transforms/InstCombine/load-store-forward.ll
Differential Revision: https://reviews.llvm.org/D120240
A generalization like this was suggested in D119754.
This is the inverse direction of D119851,
and we get all of the folds there plus the one that was missed.
There is precedence for this kind of transform in instcombine
with "or" instructions (but strangely only with that one opcode AFAICT).
Similar justification as in the other patch:
The line between instcombine and reassociate for these kinds of folds
is blurry. This doesn't appear to have much cost and gives us the
expected wins from repeated folds as seen in the last set of test diffs.
Differential Revision: https://reviews.llvm.org/D119955
This one tries to fix:
https://github.com/llvm/llvm-project/issues/53357.
Simply, this one would check (x & y) and ~(x | y) in
haveNoCommonBitsSet. Since they shouldn't have common bits (we could
traverse the case by enumerating), and we could convert this one to (x &
y) | ~(x | y) . Then the compiler could handle it in
InstCombineAndOrXor.
Further more, since ((x & y) + (~x & ~y)) would be converted to ((x & y)
+ ~(x | y)), this patch would fix it too.
https://alive2.llvm.org/ce/z/qsKzRS
Reviewed By: spatel, xbolva00, RKSimon, lebedev.ri
Differential Revision: https://reviews.llvm.org/D118094
Integer min/max operations are associative:
max (max X, C0), C1 --> max X, (max C0, C1) --> max X, NewC
https://alive2.llvm.org/ce/z/wW5HVM
This would avoid a regression when we canonicalize to min/max intrinsics
(see D98152 ).
Differential Revision: https://reviews.llvm.org/D119754
Augie Fackler