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This tends to happen a lot with bitfield code generated by clang. A simple example for x86_64 is uint64_t foo(uint64_t x) { return (x&1) << 42; } which used to compile into bloated code: shlq $42, %rdi ## encoding: [0x48,0xc1,0xe7,0x2a] movabsq $4398046511104, %rax ## encoding: [0x48,0xb8,0x00,0x00,0x00,0x00,0x00,0x04,0x00,0x00] andq %rdi, %rax ## encoding: [0x48,0x21,0xf8] ret ## encoding: [0xc3] with this patch we can fold the immediate into the and: andq $1, %rdi ## encoding: [0x48,0x83,0xe7,0x01] movq %rdi, %rax ## encoding: [0x48,0x89,0xf8] shlq $42, %rax ## encoding: [0x48,0xc1,0xe0,0x2a] ret ## encoding: [0xc3] It's possible to save another byte by using 'andl' instead of 'andq' but I currently see no way of doing that without making this code even more complicated. See the TODOs in the code. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@129990 91177308-0d34-0410-b5e6-96231b3b80d8 |
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