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Given that we're not actually reducing the instruction count in the included regression tests, I think we would call this a canonicalization step. The motivation comes from the example in PR26702: https://llvm.org/bugs/show_bug.cgi?id=26702 If we hoist the bitwise logic ahead of the bitcast, the previously unoptimizable example of: define <4 x i32> @is_negative(<4 x i32> %x) { %lobit = ashr <4 x i32> %x, <i32 31, i32 31, i32 31, i32 31> %not = xor <4 x i32> %lobit, <i32 -1, i32 -1, i32 -1, i32 -1> %bc = bitcast <4 x i32> %not to <2 x i64> %notnot = xor <2 x i64> %bc, <i64 -1, i64 -1> %bc2 = bitcast <2 x i64> %notnot to <4 x i32> ret <4 x i32> %bc2 } Simplifies to the expected: define <4 x i32> @is_negative(<4 x i32> %x) { %lobit = ashr <4 x i32> %x, <i32 31, i32 31, i32 31, i32 31> ret <4 x i32> %lobit } Differential Revision: http://reviews.llvm.org/D17583 git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@262645 91177308-0d34-0410-b5e6-96231b3b80d8 |
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