Fold (x << c1)>> c2 into a single shift if the bits shifted out aren't used.
This compiles:
int baz(long long a) { return (short)(((int)(a >>24)) >> 9); }
into:
_baz:
srwi r2, r3, 1
extsh r3, r2
blr
on PPC, instead of:
_baz:
slwi r2, r3, 8
srwi r2, r2, 9
extsh r3, r2
blr
GCC produces:
_baz:
srwi r10,r4,24
insrwi r10,r3,24,0
srawi r9,r3,24
srawi r3,r10,9
extsh r3,r3
blr
This implements CodeGen/PowerPC/shl_elim.ll
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@36221
91177308-0d34-0410-b5e6-
96231b3b80d8