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cmd/compile: teach prove about relations between constants

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Currently, we never add a relation between two constants to prove's
fact table because these are eliminated before prove runs, so it
currently doesn't handle facts like this very well even though they're
easy to prove.

We're about to start asserting some conditions that don't appear in
the SSA, but are constructed from existing SSA values that may both be
constants.

Hence, improve the fact table to understand relations between
constants by initializing the constant bounds of constant values to
the value itself, rather than noLimit.

Passes toolstash -cmp.

Change-Id: I71f8dc294e59f19433feab1c10b6d3c99b7f1e26
Reviewed-on: https://go-review.googlesource.com/102601
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: David Chase <drchase@google.com>
This commit is contained in:
Austin Clements 2018-03-23 17:21:33 -04:00
parent 87a18c6109
commit 8d8f620f68
1 changed files with 15 additions and 0 deletions
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15
src/cmd/compile/internal/ssa/prove.go
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@ -279,6 +279,21 @@ func (ft *factsTable) update(parent *Block, v, w *Value, d domain, r relation) {
old, ok := ft.limits[v.ID]
if !ok {
old = noLimit
if v.isGenericIntConst() {
switch d {
case signed:
old.min, old.max = v.AuxInt, v.AuxInt
if v.AuxInt >= 0 {
old.umin, old.umax = uint64(v.AuxInt), uint64(v.AuxInt)
}
case unsigned:
old.umin = v.AuxUnsigned()
old.umax = old.umin
if int64(old.umin) >= 0 {
old.min, old.max = int64(old.umin), int64(old.umin)
}
}
}
}
lim := noLimit
switch d {