https://bugs.llvm.org/show_bug.cgi?id=43523
Bug ID: 43523
Summary: [InstCombine] Extract high bits + sext -> Extract high
bits with sext
Product: libraries
Version: trunk
Hardware: PC
OS: Linux
Status: NEW
Severity: enhancement
Priority: P
Component: Scalar Optimizations
Assignee: unassignedb...@nondot.org
Reporter: lebedev...@gmail.com
CC: llvm-bugs@lists.llvm.org
https://godbolt.org/z/qhpAcX
int extract_high_bits_with_signext_BAD(unsigned long data, int nbits) {
return (int(data >> (64-nbits)) << (32-nbits)) >> (32-nbits);
}
int extract_high_bits_with_signext_GOOD(unsigned long data, int nbits) {
return (signed long)(data) >> (64-nbits);
}
I'm not sure yet what generalization of the pattern is there,
maybe here i can get away with just looking for that specific pattern..
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