Author: Armin Rigo <ar...@tunes.org>
Branch: arm64
Changeset: r96953:aac1bb032282
Date: 2019-07-05 06:55 +0000
http://bitbucket.org/pypy/pypy/changeset/aac1bb032282/
Log: Clean up code and comments, no longer doing copies that I've now
understood are pointless
diff --git a/rpython/translator/c/src/stacklet/switch_aarch64_gcc.h
b/rpython/translator/c/src/stacklet/switch_aarch64_gcc.h
--- a/rpython/translator/c/src/stacklet/switch_aarch64_gcc.h
+++ b/rpython/translator/c/src/stacklet/switch_aarch64_gcc.h
@@ -9,66 +9,51 @@
{
void *result;
/*
- registers to preserve: x18-x28, x29(fp), x30(lr), and v8-v15
- registers marked as clobbered: x0-x18
+ registers to preserve: x18-x28, x29(fp), and v8-v15
+ registers marked as clobbered: x0-x18, x30
- Note that x18 appears in both lists; see below.
+ Note that x18 appears in both lists; see below. We also save
+ x30 although it's also marked as clobbered, which might not
+ be necessary but doesn't hurt.
Don't assume gcc saves any register for us when generating
code for slp_switch().
The values 'save_state', 'restore_state' and 'extra' are first moved
- by gcc to some registers that are not marked as clobbered, so >= x19.
- Similarly, gcc expects 'result' to be in a register >= x19.
- We don't want x18 to be used here, because of some special meaning
- it might have.
+ by gcc to some registers that are not marked as clobbered, so between
+ x19 and x29. Similarly, gcc expects 'result' to be in a register
+ between x19 and x29. We don't want x18 to be used here, because of
+ some special meaning it might have. We don't want x30 to be used
+ here, because it is clobbered by the first "blr".
This means that three of the values we happen to save and restore
will, in fact, contain the three arguments, and one of these values
will, in fact, not be restored at all but receive 'result'.
-
- The following two points may no longer be true, because "x30" is
- now present in the clobbered list, but the extra workarounds we
- do might be safer just in case:
-
- (1) Careful writing "blr %[...]": if gcc resolves it to x30---and it
- can!---then you're in trouble, because "blr x30" does not jump
- anywhere at all (it probably loads the current position into x30
- before it jumps to x30...)
-
- (2) Also, because "%[...]" can resolve to x30, we can't use that
after
- the first call. Instead, we need to copy the values somewhere
- safe, like x24 and x25. We do that in such an order that it should
- work even if any of the "%[...]" expressions becomes x24 or x25 too.
*/
__asm__ volatile (
/* The stack is supposed to be aligned as necessary already.
- Save 13 registers from x18 to x30, plus 8 from v8 to v15 */
+ Save 12 registers from x18 to x29, plus 8 from v8 to v15 */
- "stp x29, x30, [sp, -176]!\n"
- "stp x18, x19, [sp, 16]\n"
- "stp x20, x21, [sp, 32]\n"
- "stp x22, x23, [sp, 48]\n"
- "stp x24, x25, [sp, 64]\n"
- "stp x26, x27, [sp, 80]\n"
- "str x28, [sp, 96]\n"
- "str d8, [sp, 104]\n"
- "str d9, [sp, 112]\n"
- "str d10, [sp, 120]\n"
- "str d11, [sp, 128]\n"
- "str d12, [sp, 136]\n"
- "str d13, [sp, 144]\n"
- "str d14, [sp, 152]\n"
- "str d15, [sp, 160]\n"
+ "stp x18, x19, [sp, -160]!\n"
+ "stp x20, x11, [sp, 16]\n"
+ "stp x22, x23, [sp, 32]\n"
+ "stp x24, x25, [sp, 48]\n"
+ "stp x26, x27, [sp, 64]\n"
+ "stp x28, x29, [sp, 80]\n"
+ "str d8, [sp, 96]\n"
+ "str d9, [sp, 104]\n"
+ "str d10, [sp, 112]\n"
+ "str d11, [sp, 120]\n"
+ "str d12, [sp, 128]\n"
+ "str d13, [sp, 136]\n"
+ "str d14, [sp, 144]\n"
+ "str d15, [sp, 152]\n"
"mov x0, sp\n" /* arg 1: current (old) stack pointer */
- "mov x1, %[extra]\n" /* arg 2: extra, from >= x18 */
- "mov x3, %[save_state]\n"
- "mov x24, %[restore_state]\n" /* save restore_state => x24 */
- "mov x25, x1\n" /* save extra => x25 */
- "blr x3\n" /* call save_state() */
+ "mov x1, %[extra]\n" /* arg 2: extra, from x19-x28 */
+ "blr %[save_state]\n" /* call save_state(), from x19-x28 */
/* skip the rest if the return value is null */
"cbz x0, zero\n"
@@ -77,29 +62,28 @@
/* From now on, the stack pointer is modified, but the content of the
stack is not restored yet. It contains only garbage here. */
- "mov x1, x25\n" /* arg 2: extra */
+ "mov x1, %[extra]\n" /* arg 2: extra, still from x19-x28 */
/* arg 1: current (new) stack pointer is already in x0*/
- "blr x24\n" /* call restore_state() */
+ "blr %[restore_state]\n"/* call restore_state() */
/* The stack's content is now restored. */
"zero:\n"
/* Restore all saved registers */
- "ldp x18, x19, [sp, 16]\n"
- "ldp x20, x21, [sp, 32]\n"
- "ldp x22, x23, [sp, 48]\n"
- "ldp x24, x25, [sp, 64]\n"
- "ldp x26, x27, [sp, 80]\n"
- "ldr x28, [sp, 96]\n"
- "ldr d8, [sp, 104]\n"
- "ldr d9, [sp, 112]\n"
- "ldr d10, [sp, 120]\n"
- "ldr d11, [sp, 128]\n"
- "ldr d12, [sp, 136]\n"
- "ldr d13, [sp, 144]\n"
- "ldr d14, [sp, 152]\n"
- "ldr d15, [sp, 160]\n"
- "ldp x29, x30, [sp], 176\n"
+ "ldp x20, x11, [sp, 16]\n"
+ "ldp x22, x23, [sp, 32]\n"
+ "ldp x24, x25, [sp, 48]\n"
+ "ldp x26, x27, [sp, 64]\n"
+ "ldp x28, x29, [sp, 80]\n"
+ "ldr d8, [sp, 96]\n"
+ "ldr d9, [sp, 104]\n"
+ "ldr d10, [sp, 112]\n"
+ "ldr d11, [sp, 120]\n"
+ "ldr d12, [sp, 128]\n"
+ "ldr d13, [sp, 136]\n"
+ "ldr d14, [sp, 144]\n"
+ "ldr d15, [sp, 152]\n"
+ "ldp x18, x19, [sp], 160\n"
/* Move x0 into the final location of 'result' */
"mov %[result], x0\n"
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