From a6755fc0debc3005e8bd730521ecc8dba61a24e8 Mon Sep 17 00:00:00 2001 From: Cholerae Hu Date: Fri, 31 Jul 2020 13:57:48 +0800 Subject: [PATCH] cmd/compile: check indirect connection between if block and phi block in addLocalInductiveFacts CL 244579 added guard clauses to prevent a faulty state that was possible under the incorrect logic of the uniquePred loop in addLocalInductiveFacts. That faulty state was still making the intended optimization, but not for the correct reason. Removing the faulty state also removed the overly permissive application of the optimization, and therefore made these two tests fail. We disabled the tests of this optimization in CL 244579 to allow us to quickly apply the fix in the CL. This CL now corrects the logic of the uniquePred loop in order to apply the optimization correctly. The comment above the uniquePred loop says that it will follow unique predecessors until it reaches a join point. Without updating the child node on each iteration, it cannot follow the chain of unique predecessors more than one step. Adding the update to the child node on each iteration of the loop allows the logic to follow the chain of unique predecessors until reaching a join point (because a non-unique predecessor will signify a join point). Updates #40502. Change-Id: I23d8367046a2ab3ce4be969631f9ba15dc533e6c Reviewed-on: https://go-review.googlesource.com/c/go/+/246157 Run-TryBot: Dmitri Shuralyov TryBot-Result: Go Bot Reviewed-by: David Chase Trust: Dmitri Shuralyov --- src/cmd/compile/internal/ssa/prove.go | 2 +- test/prove.go | 6 ++---- 2 files changed, 3 insertions(+), 5 deletions(-) diff --git a/src/cmd/compile/internal/ssa/prove.go b/src/cmd/compile/internal/ssa/prove.go index ce7d689f93..8a2e7c09bc 100644 --- a/src/cmd/compile/internal/ssa/prove.go +++ b/src/cmd/compile/internal/ssa/prove.go @@ -1082,7 +1082,7 @@ func addLocalInductiveFacts(ft *factsTable, b *Block) { return nil } pred, child := b.Preds[1].b, b - for ; pred != nil; pred = uniquePred(pred) { + for ; pred != nil; pred, child = uniquePred(pred), pred { if pred.Kind != BlockIf { continue } diff --git a/test/prove.go b/test/prove.go index 3c19c513b6..d37021d283 100644 --- a/test/prove.go +++ b/test/prove.go @@ -670,8 +670,7 @@ func oforuntil(b []int) { i := 0 if len(b) > i { top: - // TODO: remove the todo of next line once we complete the following optimization of CL 244579 - // println(b[i]) // todo: ERROR "Induction variable: limits \[0,\?\), increment 1$" "Proved IsInBounds$" + println(b[i]) // ERROR "Induction variable: limits \[0,\?\), increment 1$" "Proved IsInBounds$" i++ if i < len(b) { goto top @@ -721,8 +720,7 @@ func range1(b []int) { // range2 elements are larger, so they use the general form of a range loop. func range2(b [][32]int) { for i, v := range b { - // TODO: remove the todo of next line once we complete the following optimization of CL 244579 - b[i][0] = v[0] + 1 // todo: ERROR "Induction variable: limits \[0,\?\), increment 1$" "Proved IsInBounds$" + b[i][0] = v[0] + 1 // ERROR "Induction variable: limits \[0,\?\), increment 1$" "Proved IsInBounds$" if i < len(b) { // ERROR "Proved Less64$" println("x") } -- 2.50.0