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cmd/compile/internal/ssagen: fix min/max codegen, again

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The large-function phi placement algorithm evidently doesn't like the
same pseudo-variable being used to represent expressions of varying
types.

Instead, use the same tactic as used for "valVar" (ssa.go:6585--6587),
which is to just generate a fresh marker node each time.

Maybe we could just use the OMIN/OMAX nodes themselves as the key
(like we do for OANDAND/OOROR), but that just seems needlessly risky
for negligible memory savings. Using fresh marker values each time
seems obviously safe by comparison.

Fixes #61041.

Change-Id: Ie2600c9c37b599c2e26ae01f5f8a433025d7fd08
Reviewed-on: https://go-review.googlesource.com/c/go/+/506679
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Cuong Manh Le <cuong.manhle.vn@gmail.com>
This commit is contained in:
Matthew Dempsky 2023-06-27 16:51:24 -07:00 committed by Carlos Amedee
parent a3093eca64
commit 79d4defa75
2 changed files with 10 additions and 2 deletions
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5
src/cmd/compile/internal/ssagen/ssa.go
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@ -949,7 +949,6 @@ var (
typVar = ssaMarker("typ") typVar = ssaMarker("typ")
okVar = ssaMarker("ok") okVar = ssaMarker("ok")
deferBitsVar = ssaMarker("deferBits") deferBitsVar = ssaMarker("deferBits")
ternaryVar = ssaMarker("ternary")
) )
// startBlock sets the current block we're generating code in to b. // startBlock sets the current block we're generating code in to b.
@ -3621,6 +3620,10 @@ func (s *state) minMax(n *ir.CallExpr) *ssa.Value {
// ternary emits code to evaluate cond ? x : y. // ternary emits code to evaluate cond ? x : y.
func (s *state) ternary(cond, x, y *ssa.Value) *ssa.Value { func (s *state) ternary(cond, x, y *ssa.Value) *ssa.Value {
// Note that we need a new ternaryVar each time (unlike okVar where we can
// reuse the variable) because it might have a different type every time.
ternaryVar := ssaMarker("ternary")
bThen := s.f.NewBlock(ssa.BlockPlain) bThen := s.f.NewBlock(ssa.BlockPlain)
bElse := s.f.NewBlock(ssa.BlockPlain) bElse := s.f.NewBlock(ssa.BlockPlain)
bEnd := s.f.NewBlock(ssa.BlockPlain) bEnd := s.f.NewBlock(ssa.BlockPlain)

7
test/fixedbugs/issue60982.go
View File

@ -6,8 +6,13 @@
package main package main
func f(x int) int { func f(x int, b bool) int {
if x >= 1000 { if x >= 1000 {
if b { // from #61041
var a struct{ f int64 }
_ = max(0, a.f)
}
return max(x, 2000) return max(x, 2000)
} }
// generate 1000 basic blocks to put this function // generate 1000 basic blocks to put this function