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[LoopSimplifyCFG] Don't delete LCSSA Phis

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When removing edges, we also update Phi inputs and may end up removing
a Phi if it has only one input. We should not do it for edges that leave the current
loop because these Phis are LCSSA Phis and need to be preserved.

Thanks @dmgreen	for finding this!

Differential Revision: https://reviews.llvm.org/D54841

llvm-svn: 347484
This commit is contained in:
Max Kazantsev 2018-11-23 07:56:47 +00:00
parent fa5d441135
commit 4090cb9a08
2 changed files with 56 additions and 1 deletions
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5
lib/Transforms/Scalar/LoopSimplifyCFG.cpp
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@ -249,7 +249,10 @@ private:
for (auto *Succ : successors(BB))
if (Succ != TheOnlySucc) {
DeadSuccessors.insert(Succ);
Succ->removePredecessor(BB);
// If our successor lies in a different loop, we don't want to remove
// the one-input Phi because it is a LCSSA Phi.
bool PreserveLCSSAPhi = !L.contains(Succ);
Succ->removePredecessor(BB, PreserveLCSSAPhi);
}
IRBuilder<> Builder(BB->getContext());

52
test/Transforms/LoopSimplifyCFG/lcssa.ll Normal file
View File

@ -0,0 +1,52 @@
; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
; RUN: opt -S -loop-simplifycfg -verify-loop-info -verify-dom-info -verify-loop-lcssa < %s | FileCheck %s
; RUN: opt -S -passes='require<domtree>,loop(simplify-cfg)' -verify-loop-info -verify-dom-info -verify-loop-lcssa < %s | FileCheck %s
; RUN: opt -S -loop-simplifycfg -enable-mssa-loop-dependency=true -verify-memoryssa -verify-loop-info -verify-dom-info -verify-loop-lcssa < %s | FileCheck %s
target datalayout = "e-m:e-i8:8:32-i16:16:32-i64:64-i128:128-n32:64-S128"
define void @c() {
; CHECK-LABEL: @c(
; CHECK-NEXT: entry:
; CHECK-NEXT: br label [[D:%.*]]
; CHECK: d.loopexit:
; CHECK-NEXT: [[DOTLCSSA:%.*]] = phi i32 [ [[TMP1:%.*]], [[FOR_COND:%.*]] ]
; CHECK-NEXT: br label [[D]]
; CHECK: d:
; CHECK-NEXT: [[TMP0:%.*]] = phi i32 [ undef, [[ENTRY:%.*]] ], [ [[DOTLCSSA]], [[D_LOOPEXIT:%.*]] ]
; CHECK-NEXT: br label [[FOR_COND]]
; CHECK: for.cond:
; CHECK-NEXT: [[TMP1]] = phi i32 [ [[TMP0]], [[D]] ], [ 0, [[IF_END:%.*]] ]
; CHECK-NEXT: [[TOBOOL2:%.*]] = icmp eq i32 [[TMP1]], 0
; CHECK-NEXT: br i1 [[TOBOOL2]], label [[IF_END]], label [[D_LOOPEXIT]]
; CHECK: if.end:
; CHECK-NEXT: br label [[FOR_COND]]
;
entry:
br label %d
d.loopexit: ; preds = %if.end.7, %for.body
%.lcssa = phi i32 [ %1, %for.body ], [ 0, %if.end.7 ]
br label %d
d: ; preds = %d.loopexit, %entry
%0 = phi i32 [ undef, %entry ], [ %.lcssa, %d.loopexit ]
br label %for.cond
for.cond: ; preds = %if.end.8, %d
%1 = phi i32 [ %0, %d ], [ 0, %if.end.8 ]
br label %for.body
for.body: ; preds = %for.cond
%tobool2 = icmp eq i32 %1, 0
br i1 %tobool2, label %if.end, label %d.loopexit
if.end: ; preds = %for.body
br label %if.end.7
if.end.7: ; preds = %if.end
br i1 true, label %if.end.8, label %d.loopexit
if.end.8: ; preds = %if.end.7
br label %for.cond
}