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tcg/mips: fix add2

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The add2 code in the tcg_out_addsub2 function doesn't take into account
the case where rl == al == bl. In that case we can't compute the carry
after the addition. As it corresponds to a multiplication by 2, the
carry bit is the bit 31.

While this is a corner case, this prevents x86-64 guests to boot on a
MIPS host.

Backports commit c99d69694af4ed15b33e3f7c2e3ef6972c14358d from qemu
This commit is contained in:
Aurelien Jarno 2018-02-14 17:19:19 -05:00 committed by Lioncash
parent 4e68b4167d
commit 45927edecf
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1 changed files with 3 additions and 0 deletions
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qemu/tcg/mips/tcg-target.c
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@ -1271,6 +1271,9 @@ static void tcg_out_addsub2(TCGContext *s, TCGReg rl, TCGReg rh, TCGReg al,
if (cbl) {
tcg_out_opc_imm(s, OPC_ADDIU, rl, al, bl);
tcg_out_opc_imm(s, OPC_SLTIU, TCG_TMP0, rl, bl);
} else if (rl == al && rl == bl) {
tcg_out_opc_sa(s, OPC_SRL, TCG_TMP0, al, 31);
tcg_out_opc_reg(s, OPC_ADDU, rl, al, bl);
} else {
tcg_out_opc_reg(s, OPC_ADDU, rl, al, bl);
tcg_out_opc_reg(s, OPC_SLTU, TCG_TMP0, rl, (rl == bl ? al : bl));