Previously we emitted something like
rotl(x, n) {
n &= bitwidth-1;
return n != 0 ? ((x << n) | (x >> (bitwidth - n)) : x;
}
We use a select to avoid the undefined behavior on the (bitwidth - n) shift.
The middle and backend don't really recognize this as a rotate and end up emitting a cmov or control flow because of the select.
A better pattern is (x << (n & mask)) | (x << (-n & mask)) where mask is bitwidth - 1.
Fixes the main complaint in PR37387. There's still some work to be done if the user writes that sequence directly on a short or char where type promotion rules can prevent it from being recognized. The builtin is emitting direct IR with unpromoted types so that isn't a problem for it.
Differential Revision: https://reviews.llvm.org/D46656
llvm-svn: 331943
This allows for -fms-extensions to work the same on LP64. For example,
_BitScanReverse is expected to be 32-bit, matching Windows/LLP64, even
though long is 64-bit on x86_64 Darwin or Linux (LP64).
Implement this by adding a new character code 'N', which is 'int' if
the target is LP64 and the same 'L' otherwise
Differential Revision: https://reviews.llvm.org/D34377
rdar://problem/32599746
llvm-svn: 305875
Craig Topper