bce8af97e3
When an instruction has multiple valid encodings, such as with and without a REX prefix on x86-64, Cretonne typically picks the encoding which gives the register allocator the most flexibility, which is typically the longest encoding. This patch adds a pass that runs after register allocation that picks the smallest encoding, working within the constraints of the register allocator's choices. The result is smaller and easier to read encodings. In the future, we may want to merge this pass into the relaxation pass, or possibly fold it into the final encoding step, however for now, a discrete pass will suffice.
30 lines
800 B
Plaintext
30 lines
800 B
Plaintext
test binemit
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set is_64bit=1
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set opt_level=best
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isa x86
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; Test that instruction shrinking eliminates REX prefixes when possible.
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; The binary encodings can be verified with the command:
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;
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; sed -ne 's/^ *; asm: *//p' filetests/isa/x86/shrink.cton | llvm-mc -show-encoding -triple=x86_64
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;
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function %test_shrinking(i32) -> i32 {
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ebb0(v0: i32 [ %rdi ]):
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; asm: movl $0x2,%eax
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[-,%rcx] v1 = iconst.i32 2 ; bin: b9 00000002
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; asm: subl %ecx,%edi
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[-,%rdi] v2 = isub v0, v1 ; bin: 29 cf
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return v2
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}
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function %test_not_shrinking(i32) -> i32 {
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ebb0(v0: i32 [ %r8 ]):
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; asm: movl $0x2,%eax
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[-,%rcx] v1 = iconst.i32 2 ; bin: b9 00000002
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; asm: subl %ecx,%edi
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[-,%r8] v2 = isub v0, v1 ; bin: 41 29 c8
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return v2
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}
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