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target-arm: Simplify insn_crosses_page() 

Recent changes have left insn_crosses_page() more complicated
than it needed to be:
 * it's only called from thumb_tr_translate_insn() so we know
   for certain that we're looking at a Thumb insn
 * the caller's check for dc->pc >= dc->next_page_start - 3
   means that dc->pc can't possibly be 4 aligned, so there's
   no need to check that (the check was partly there to ensure
   that we didn't treat an ARM insn as Thumb, I think)
 * we now have thumb_insn_is_16bit() which lets us do a precise
   check of the length of the next insn, rather than opencoding
   an inaccurate check

Simplify it down to just loading the first half of the insn
and calling thumb_insn_is_16bit() on it.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 1507556919-24992-8-git-send-email-peter.maydell@linaro.org
This commit is contained in:
Peter Maydell 2017-10-09 14:48:37 +01:00
parent 296e5a0a6c
commit 5b8d7289e9
1 changed files with 6 additions and 21 deletions
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27
target/arm/translate.c
View File

@ -11872,29 +11872,14 @@ static bool insn_crosses_page(CPUARMState *env, DisasContext *s)
{
/* Return true if the insn at dc->pc might cross a page boundary.
* (False positives are OK, false negatives are not.)
* We know this is a Thumb insn, and our caller ensures we are
* only called if dc->pc is less than 4 bytes from the page
* boundary, so we cross the page if the first 16 bits indicate
* that this is a 32 bit insn.
*/
uint16_t insn;
uint16_t insn = arm_lduw_code(env, s->pc, s->sctlr_b);
if ((s->pc & 3) == 0) {
/* At a 4-aligned address we can't be crossing a page */
return false;
}
/* This must be a Thumb insn */
insn = arm_lduw_code(env, s->pc, s->sctlr_b);
if ((insn >> 11) >= 0x1d) {
/* Top five bits 0b11101 / 0b11110 / 0b11111 : this is the
* First half of a 32-bit Thumb insn. Thumb-1 cores might
* end up actually treating this as two 16-bit insns (see the
* code at the start of disas_thumb2_insn()) but we don't bother
* to check for that as it is unlikely, and false positives here
* are harmless.
*/
return true;
}
/* Definitely a 16-bit insn, can't be crossing a page. */
return false;
return !thumb_insn_is_16bit(s, insn);
}
static int arm_tr_init_disas_context(DisasContextBase *dcbase,