Missing transformation rotate(x) == 0 to x == 0 #50908
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To generalize, the rotate amount can be anything if the result is checking if all bits are set/clear. So I think there are 8 cases to test:
So something like this (and we can substitute fshr/fshl): |
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Should be fixed with: |
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Extended Description
bool test1(unsigned long long x)
{
unsigned long long r = (x << 32) | (x >> 32);
return r != 0;
}
bool test2(unsigned long long x)
{
unsigned long long r = (x << 32) | (x >> 32);
return r == ~0ULL;
}
Trunk -O3:
test1(unsigned long long): # @test1(unsigned long long)
rol rdi, 32
test rdi, rdi
setne al
ret
test2(unsigned long long): # @test2(unsigned long long)
rol rdi, 32
cmp rdi, -1
sete al
ret
test3(unsigned long long): # @test3(unsigned long long)
rol rdi, 32
test rdi, rdi
setne al
ret
Current codegen:
https://godbolt.org/z/q78xxhWe4
define i1 @src(i64 %0) {
%1:
%2 = fshr i64 %0, i64 %0, i64 32
%3 = icmp ne i64 %2, 0
ret i1 %3
}
=>
define i1 @tgt(i64 %0) {
%1:
%2 = icmp ne i64 %0, 0
ret i1 %2
}
Transformation seems to be correct!
define i1 @src(i64 %0) {
%1:
%2 = fshr i64 %0, i64 %0, i64 32
%3 = icmp ne i64 %2, -1
ret i1 %3
}
=>
define i1 @tgt(i64 %0) {
%1:
%2 = icmp ne i64 %0, -1
ret i1 %2
}
Transformation seems to be correct!
Alive:
https://alive2.llvm.org/ce/z/kmrBvv
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