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uint32_t hi(uint64_t res) { uint_32t hi = res >> 32; return !hi; } llvm IR looks like this: define i32 @hi(i64 %res) nounwind uwtable ssp { entry: %lnot = icmp ult i64 %res, 4294967296 %lnot.ext = zext i1 %lnot to i32 ret i32 %lnot.ext } The optimizer has optimize away the right shift and truncate but the resulting constant is too large to fit in the 32-bit immediate field. The resulting x86 code is worse as a result: movabsq $4294967296, %rax ## imm = 0x100000000 cmpq %rax, %rdi sbbl %eax, %eax andl $1, %eax This patch teaches the x86 lowering code to handle ult against a large immediate with trailing zeros. It will issue a right shift and a truncate followed by a comparison against a shifted immediate. shrq $32, %rdi testl %edi, %edi sete %al movzbl %al, %eax It also handles a ugt comparison against a large immediate with trailing bits set. i.e. X > 0x0ffffffff -> (X >> 32) >= 1 rdar://11866926 git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@160312 91177308-0d34-0410-b5e6-96231b3b80d8 |
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