[PATCH] D62418: [MustExecute] Improve MustExecute to correctly handle loop nest
Whitney via Phabricator via llvm-commits
llvm-commits at lists.llvm.org
Sat May 25 09:41:57 PDT 2019
Whitney updated this revision to Diff 201406.
Whitney added a comment.
Addressed all review comments.
Repository:
rL LLVM
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D62418/new/
https://reviews.llvm.org/D62418
Files:
llvm/lib/Analysis/MustExecute.cpp
llvm/test/Analysis/MustExecute/loop-header.ll
Index: llvm/test/Analysis/MustExecute/loop-header.ll
===================================================================
--- llvm/test/Analysis/MustExecute/loop-header.ll
+++ llvm/test/Analysis/MustExecute/loop-header.ll
@@ -83,17 +83,15 @@
ret i1 false
}
-; FIXME: everything in inner loop header should be must execute
-; for outer as well
define i1 @nested_no_throw(i32* noalias %p, i32 %high) {
; CHECK-LABEL: @nested_no_throw
; CHECK-LABEL: loop: ; preds = %next
; CHECK: %iv = phi i32 [ 0, %entry ], [ %iv.next, %next ] ; (mustexec in: loop)
; CHECK: br label %inner_loop ; (mustexec in: loop)
; CHECK-LABEL: inner_loop:
-; CHECK: %v = load i32, i32* %p ; (mustexec in: inner_loop)
-; CHECK: %inner.test = icmp eq i32 %v, 0 ; (mustexec in: inner_loop)
-; CHECK: br i1 %inner.test, label %inner_loop, label %next ; (mustexec in: inner_loop)
+; CHECK: %v = load i32, i32* %p ; (mustexec in 2 loops: inner_loop, loop)
+; CHECK: %inner.test = icmp eq i32 %v, 0 ; (mustexec in 2 loops: inner_loop, loop)
+; CHECK: br i1 %inner.test, label %inner_loop, label %next ; (mustexec in 2 loops: inner_loop, loop)
; CHECK-LABEL: next:
; CHECK: %iv.next = add nuw nsw i32 %iv, 1 ; (mustexec in: loop)
; CHECK: %exit.test = icmp slt i32 %iv, %high ; (mustexec in: loop)
Index: llvm/lib/Analysis/MustExecute.cpp
===================================================================
--- llvm/lib/Analysis/MustExecute.cpp
+++ llvm/lib/Analysis/MustExecute.cpp
@@ -193,7 +193,8 @@
SmallPtrSet<const BasicBlock *, 4> Predecessors;
collectTransitivePredecessors(CurLoop, BB, Predecessors);
- // Make sure that all successors of all predecessors of BB are either:
+ // Make sure that all successors of, all predecessors of BB which are not
+ // dominated by BB, are either:
// 1) BB,
// 2) Also predecessors of BB,
// 3) Exit blocks which are not taken on 1st iteration.
@@ -203,6 +204,12 @@
// Predecessor block may throw, so it has a side exit.
if (blockMayThrow(Pred))
return false;
+
+ // BB dominates Pred, so if Pred runs, BB must run.
+ // This is true when Pred is a loop latch.
+ if (DT->dominates(BB, Pred))
+ continue;
+
for (auto *Succ : successors(Pred))
if (CheckedSuccessors.insert(Succ).second &&
Succ != BB && !Predecessors.count(Succ))
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