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cmd/internal/obj/ppc64: improve large prologue generation

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Avoid needing an unsafe section to store LR and adjust SP
for large constants by using the stdux (MOVDU) instruction.

This is also a few instructions shorter as the large
constant adjustment is only created once.

Change-Id: I6ff7a24181cdadb1846a33129fc148dcf59b76d5
Reviewed-on: https://go-review.googlesource.com/c/go/+/710197
Reviewed-by: Keith Randall <khr@google.com>
Reviewed-by: Keith Randall <khr@golang.org>
Reviewed-by: David Chase <drchase@google.com>
Auto-Submit: Keith Randall <khr@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
This commit is contained in:
Paul Murphy
2025-10-08 14:34:09 -05:00
committed by Gopher Robot
parent b0dcb95542
commit 694182d77b
1 changed files with 17 additions and 23 deletions
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40
src/cmd/internal/obj/ppc64/obj9.go
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@@ -903,44 +903,38 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {
q.To.Reg = REGSP
q.Spadj = autosize
} else {
// Frame size is too large for a MOVDU instruction.
// Store link register before decrementing SP, so if a signal comes
// during the execution of the function prologue, the traceback
// code will not see a half-updated stack frame.
// This sequence is not async preemptible, as if we open a frame
// at the current SP, it will clobber the saved LR.
// Frame size is too large for an stdu MOVDU instruction, use stdux MOVDU.
q = obj.Appendp(q, c.newprog)
q.As = AMOVD
q.Pos = p.Pos
q.From.Type = obj.TYPE_REG
q.From.Reg = REG_LR
q.To.Type = obj.TYPE_REG
q.To.Reg = REG_R29 // REGTMP may be used to synthesize large offset in the next instruction
q = c.ctxt.StartUnsafePoint(q, c.newprog)
q.To.Reg = REG_R29
// Create stack adjustment in REGTMP
q = obj.Appendp(q, c.newprog)
q.As = AMOVD
q.Pos = p.Pos
q.From.Type = obj.TYPE_REG
q.From.Reg = REG_R29
q.To.Type = obj.TYPE_MEM
q.To.Offset = int64(-autosize)
q.To.Reg = REGSP
prologueEnd = q
q = obj.Appendp(q, c.newprog)
q.As = AADD
q.Pos = p.Pos
q.From.Type = obj.TYPE_CONST
q.From.Offset = int64(-autosize)
q.To.Type = obj.TYPE_REG
q.To.Reg = REGSP
q.Spadj = +autosize
q.To.Reg = REGTMP
q = c.ctxt.EndUnsafePoint(q, c.newprog, -1)
prologueEnd = q
// MOVDU R29, R31(R1)
q = obj.Appendp(q, c.newprog)
q.As = AMOVDU
q.Pos = p.Pos
q.From.Type = obj.TYPE_REG
q.From.Reg = REG_R29
q.To.Type = obj.TYPE_MEM
q.To.Reg = REGTMP
q.To.Index = REGSP
q.Spadj = autosize
}
prologueEnd.Pos = prologueEnd.Pos.WithXlogue(src.PosPrologueEnd)
} else if c.cursym.Func().Text.Mark&LEAF == 0 {
// A very few functions that do not return to their caller