https://llvm.org/bugs/show_bug.cgi?id=23996
Bug ID: 23996
Summary: Incorrect/inefficient pushw encodings for x86-64
targets
Product: libraries
Version: trunk
Hardware: PC
OS: All
Status: NEW
Severity: normal
Priority: P
Component: Backend: X86
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected]
Classification: Unclassified
Below is an illustration of the problems. The first pushw is incorrectly
encoded as pushq. The second pushw is encoded correctly but inefficiently as it
uses a 16-bit immediate rather than an 8-bit immediate.
Note also that the gas-generated instruction "66 6a 2a" is incorrectly printed
by llvm-objdump as pushq.
All 3 problems can be fixed by fixing the instruction descriptors for the
16-bit push immediate forms.
------------------------------
bash-4.3$ cat t.s
.section push,"x"
pushw $foo
pushw $42
bash-4.3$ llvm-mc t.s -filetype=obj -o - | llvm-objdump -d -
<stdin>: file format ELF64-x86-64
Disassembly of section push:
push:
0: 68 00 00 00 00 pushq $0
5: 66 68 2a 00 pushw $42
bash-4.3$ gcc -c t.s && llvm-objdump -d t.o
t.o: file format ELF64-x86-64
Disassembly of section push:
push:
0: 66 68 00 00 pushw $0
4: 66 6a 2a pushq $42
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