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[dev.ssa] cmd/compile: allocate the flag register in a separate pass

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Spilling/restoring flag values is a pain to do during regalloc.
Instead, allocate the flag register in a separate pass.  Regalloc then
operates normally on any flag recomputation instructions.

Change-Id: Ia1c3d9e6eff678861193093c0b48a00f90e4156b
Reviewed-on: https://go-review.googlesource.com/17694
Reviewed-by: David Chase <drchase@google.com>
This commit is contained in:
Keith Randall 2015-12-09 15:58:18 -08:00
parent 09ffa0c4c7
commit c140df0326
6 changed files with 162 additions and 50 deletions
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11
src/cmd/compile/internal/ssa/compile.go
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@ -97,9 +97,10 @@ var passes = [...]pass{
{"lowered cse", cse},
{"lowered deadcode", deadcode},
{"checkLower", checkLower},
{"critical", critical}, // remove critical edges
{"layout", layout}, // schedule blocks
{"schedule", schedule}, // schedule values
{"critical", critical}, // remove critical edges
{"layout", layout}, // schedule blocks
{"schedule", schedule}, // schedule values
{"flagalloc", flagalloc}, // allocate flags register
{"regalloc", regalloc},
{"stackalloc", stackalloc},
}
@ -142,6 +143,10 @@ var passOrder = [...]constraint{
// checkLower must run after lowering & subsequent dead code elim
{"lower", "checkLower"},
{"lowered deadcode", "checkLower"},
// flagalloc needs instructions to be scheduled.
{"schedule", "flagalloc"},
// regalloc needs flags to be allocated first.
{"flagalloc", "regalloc"},
}
func init() {