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[SROA] Handle PHI with multiple duplicate predecessors

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Summary:
The verifier accepts PHI nodes with multiple entries for the
same basic block, as long as the value is the same.

As seen in PR37203, SROA did not handle such PHI nodes properly
when speculating loads over the PHI, since it inserted multiple
loads in the predecessor block and changed the PHI into having
multiple entries for the same basic block, but with different
values.

This patch teaches SROA to reuse the same speculated load for
each PHI duplicate entry in such situations.

Resolves: https://bugs.llvm.org/show_bug.cgi?id=37203

Reviewers: uabelho, chandlerc, hfinkel, bkramer, efriedma

Reviewed By: efriedma

Subscribers: dberlin, efriedma, llvm-commits

Differential Revision: https://reviews.llvm.org/D46426

llvm-svn: 332577
This commit is contained in:
Bjorn Pettersson 2018-05-17 07:21:41 +00:00
parent 84e6d14321
commit 69e45c2eaf
2 changed files with 64 additions and 1 deletions
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14
lib/Transforms/Scalar/SROA.cpp
View File

@ -1261,10 +1261,21 @@ static void speculatePHINodeLoads(PHINode &PN) {
}
// Inject loads into all of the pred blocks.
DenseMap<BasicBlock*, Value*> InjectedLoads;
for (unsigned Idx = 0, Num = PN.getNumIncomingValues(); Idx != Num; ++Idx) {
BasicBlock *Pred = PN.getIncomingBlock(Idx);
TerminatorInst *TI = Pred->getTerminator();
Value *InVal = PN.getIncomingValue(Idx);
// A PHI node is allowed to have multiple (duplicated) entries for the same
// basic block, as long as the value is the same. So if we already injected
// a load in the predecessor, then we should reuse the same load for all
// duplicated entries.
if (Value* V = InjectedLoads.lookup(Pred)) {
NewPN->addIncoming(V, Pred);
continue;
}
TerminatorInst *TI = Pred->getTerminator();
IRBuilderTy PredBuilder(TI);
LoadInst *Load = PredBuilder.CreateLoad(
@ -1274,6 +1285,7 @@ static void speculatePHINodeLoads(PHINode &PN) {
if (AATags)
Load->setAAMetadata(AATags);
NewPN->addIncoming(Load, Pred);
InjectedLoads[Pred] = Load;
}
LLVM_DEBUG(dbgs() << " speculated to: " << *NewPN << "\n");

51
test/Transforms/SROA/phi-with-duplicate-pred.ll Normal file
View File

@ -0,0 +1,51 @@
; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
; RUN: opt < %s -sroa -S | FileCheck %s
target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:32:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-n8:16:32:64"
@a = external global i16, align 1
define void @f2() {
; CHECK-LABEL: @f2(
; CHECK-NEXT: entry:
; CHECK-NEXT: br i1 undef, label [[IF_THEN:%.*]], label [[IF_ELSE:%.*]]
; CHECK: if.then:
; CHECK-NEXT: br label [[CLEANUP:%.*]]
; CHECK: cleanup:
; CHECK-NEXT: [[G_0_SROA_SPECULATE_LOAD_CLEANUP:%.*]] = load i16, i16* @a, align 1
; CHECK-NEXT: switch i32 2, label [[CLEANUP7:%.*]] [
; CHECK-NEXT: i32 0, label [[LBL1:%.*]]
; CHECK-NEXT: i32 2, label [[LBL1]]
; CHECK-NEXT: ]
; CHECK: if.else:
; CHECK-NEXT: br label [[LBL1]]
; CHECK: lbl1:
; CHECK-NEXT: [[G_0_SROA_SPECULATED:%.*]] = phi i16 [ [[G_0_SROA_SPECULATE_LOAD_CLEANUP]], [[CLEANUP]] ], [ [[G_0_SROA_SPECULATE_LOAD_CLEANUP]], [[CLEANUP]] ], [ undef, [[IF_ELSE]] ]
; CHECK-NEXT: unreachable
; CHECK: cleanup7:
; CHECK-NEXT: ret void
;
entry:
%e = alloca i16, align 1
br i1 undef, label %if.then, label %if.else
if.then: ; preds = %entry
br label %cleanup
cleanup: ; preds = %if.then
switch i32 2, label %cleanup7 [
i32 0, label %lbl1
i32 2, label %lbl1
]
if.else: ; preds = %entry
br label %lbl1
lbl1: ; preds = %if.else, %cleanup, %cleanup
%g.0 = phi i16* [ @a, %cleanup ], [ @a, %cleanup ], [ %e, %if.else ]
%0 = load i16, i16* %g.0, align 1
unreachable
cleanup7: ; preds = %cleanup
ret void
}