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[LCSSA] Post-process PHI-nodes created by SSAUpdate when constructing LCSSA form. 

Summary:
SSAUpdate might insert PHI-nodes inside loops, which can break LCSSA
form unless we fix it up.

This fixes PR28424.

Reviewers: sanjoy, chandlerc, hfinkel

Subscribers: uabelho, llvm-commits

Differential Revision: http://reviews.llvm.org/D21997

llvm-svn: 275883
This commit is contained in:
Michael Zolotukhin 2016-07-18 19:05:08 +00:00
parent 9670f847b8
commit 7a3040dc83
2 changed files with 97 additions and 1 deletions
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11
llvm/lib/Transforms/Utils/LCSSA.cpp
View File

@ -115,7 +115,8 @@ bool llvm::formLCSSAForInstructions(SmallVectorImpl<Instruction *> &Worklist,
SmallVector<PHINode *, 16> AddedPHIs;
SmallVector<PHINode *, 8> PostProcessPHIs;
SSAUpdater SSAUpdate;
SmallVector<PHINode *, 4> InsertedPHIs;
SSAUpdater SSAUpdate(&InsertedPHIs);
SSAUpdate.Initialize(I->getType(), I->getName());
// Insert the LCSSA phi's into all of the exit blocks dominated by the
@ -184,6 +185,14 @@ bool llvm::formLCSSAForInstructions(SmallVectorImpl<Instruction *> &Worklist,
// Otherwise, do full PHI insertion.
SSAUpdate.RewriteUse(*UseToRewrite);
// SSAUpdater might have inserted phi-nodes inside other loops. We'll need
// to post-process them to keep LCSSA form.
for (PHINode *InsertedPN : InsertedPHIs) {
if (auto *OtherLoop = LI.getLoopFor(InsertedPN->getParent()))
if (!L->contains(OtherLoop))
PostProcessPHIs.push_back(InsertedPN);
}
}
// Post process PHI instructions that were inserted into another disjoint

87
llvm/test/Transforms/LCSSA/pr28424.ll Normal file
View File

@ -0,0 +1,87 @@
; RUN: opt < %s -lcssa -S -o - | FileCheck %s
target triple = "x86_64-unknown-linux-gnu"
; PR28424
; Here LCSSA adds phi-nodes for %x into the loop exits. Then, SSAUpdater needs
; to insert phi-nodes to merge these values. That creates a new def, which in
; its turn needs another LCCSA phi-node, and this test ensures that we insert
; it.
; CHECK-LABEL: @foo1
define internal i32 @foo1() {
entry:
br label %header
header:
%x = add i32 0, 1
br i1 undef, label %if, label %loopexit1
if:
br i1 undef, label %latch, label %loopexit2
latch:
br i1 undef, label %header, label %loopexit3
; CHECK: loopexit1:
; CHECK: %x.lcssa = phi i32 [ %x, %header ]
loopexit1:
br label %loop_with_insert_point
; CHECK: loopexit2:
; CHECK: %x.lcssa1 = phi i32 [ %x, %if ]
loopexit2:
br label %exit
; CHECK: loopexit3:
; CHECK: %x.lcssa2 = phi i32 [ %x, %latch ]
loopexit3:
br label %loop_with_insert_point
; CHECK: loop_with_insert_point:
; CHECK: %x4 = phi i32 [ %x4, %loop_with_insert_point ], [ %x.lcssa2, %loopexit3 ], [ %x.lcssa, %loopexit1 ]
loop_with_insert_point:
br i1 undef, label %loop_with_insert_point, label %bb
; CHECK: bb:
; CHECK: %x4.lcssa = phi i32 [ %x4, %loop_with_insert_point ]
bb:
br label %exit
; CHECK: exit:
; CHECK: %x3 = phi i32 [ %x4.lcssa, %bb ], [ %x.lcssa1, %loopexit2 ]
exit:
ret i32 %x
}
; CHECK-LABEL: @foo2
define internal i32 @foo2() {
entry:
br label %header
header:
%x = add i32 0, 1
br i1 undef, label %latch, label %loopexit1
latch:
br i1 undef, label %header, label %loopexit2
; CHECK: loopexit1:
; CHECK: %x.lcssa = phi i32 [ %x, %header ]
loopexit1:
br label %loop_with_insert_point
; CHECK: loopexit2:
; CHECK: %x.lcssa1 = phi i32 [ %x, %latch ]
loopexit2:
br label %loop_with_insert_point
; CHECK: loop_with_insert_point:
; CHECK: %x2 = phi i32 [ %x2, %loop_with_insert_point ], [ %x.lcssa1, %loopexit2 ], [ %x.lcssa, %loopexit1 ]
loop_with_insert_point:
br i1 undef, label %loop_with_insert_point, label %exit
; CHECK: exit:
; CHECK: %x2.lcssa = phi i32 [ %x2, %loop_with_insert_point ]
exit:
ret i32 %x
}