[MC] Conditional jumps are encoded sub-optimally

[jsonn]

Bugzilla Link	9290
Resolution	FIXED
Resolved on	May 06, 2011 09:36
Version	trunk
OS	Linux

Extended Description

Consider the follow input fragment:

je 1f
1:

Expect result:
0x74 0x00

Current result:

0x0f 0x84 0x00 0x00 0x00 0x00

[llvmbot]

Hi Jörg, could you clarify this? I tried to reproduce it and failed:

$ llvm-mc -assemble -filetype=obj pr9290.s -o pr9290.o
$ objdump -d pr9290.o

pr9290.o: file format elf64-x86-64

Disassembly of section .text:

0000000000000000 <.text>:
0: 74 00 je 0x2

[llvmbot]

It happens with clang -c!

$ clang -c pr9290.s -o pr9290.o
$ objdump -d pr9290.o

pr9290.o: file format elf64-x86-64

Disassembly of section .text:

0000000000000000 <.text>:
0: 0f 84 00 00 00 00 je 0x6

Uh oh.

[llvmbot]

This is MC relaxing everything at -O0.

[llvmbot]

Reopening.

It is expected that at -O0 clang will relax everything when compiling from C, but it would be nice for it to perform as a regular assembler when given an asm file.

A corner case is the we should not change the behavior when -save-temps is given.