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[IndVars] Fix corner case with unreachable Phi inputs. PR40454 

Logic in `getInsertPointForUses` doesn't account for a corner case when `Def`
only comes to a Phi user from unreachable blocks. In this case, the incoming
value may be arbitrary (and not even available in the input block) and break
the loop-related invariants that are asserted below.

In fact, if we encounter this situation, no IR modification is needed. This
Phi will be simplified away with nearest cleanup.

Differential Revision: https://reviews.llvm.org/D58045
Reviewed By: spatel

llvm-svn: 353816
This commit is contained in:
Max Kazantsev 2019-02-12 09:59:44 +00:00
parent 8e0d5ac715
commit 2a184af221
2 changed files with 44 additions and 9 deletions
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26
llvm/lib/Transforms/Scalar/IndVarSimplify.cpp
View File

@ -217,7 +217,9 @@ bool IndVarSimplify::isValidRewrite(Value *FromVal, Value *ToVal) {
/// Determine the insertion point for this user. By default, insert immediately
/// before the user. SCEVExpander or LICM will hoist loop invariants out of the
/// loop. For PHI nodes, there may be multiple uses, so compute the nearest
/// common dominator for the incoming blocks.
/// common dominator for the incoming blocks. A nullptr can be returned if no
/// viable location is found: it may happen if User is a PHI and Def only comes
/// to this PHI from unreachable blocks.
static Instruction *getInsertPointForUses(Instruction *User, Value *Def,
DominatorTree *DT, LoopInfo *LI) {
PHINode *PHI = dyn_cast<PHINode>(User);
@ -230,6 +232,10 @@ static Instruction *getInsertPointForUses(Instruction *User, Value *Def,
continue;
BasicBlock *InsertBB = PHI->getIncomingBlock(i);
if (!DT->isReachableFromEntry(InsertBB))
continue;
if (!InsertPt) {
InsertPt = InsertBB->getTerminator();
continue;
@ -237,7 +243,11 @@ static Instruction *getInsertPointForUses(Instruction *User, Value *Def,
InsertBB = DT->findNearestCommonDominator(InsertPt->getParent(), InsertBB);
InsertPt = InsertBB->getTerminator();
}
assert(InsertPt && "Missing phi operand");
// If we have skipped all inputs, it means that Def only comes to Phi from
// unreachable blocks.
if (!InsertPt)
return nullptr;
auto *DefI = dyn_cast<Instruction>(Def);
if (!DefI)
@ -1307,10 +1317,12 @@ WidenIV::WidenedRecTy WidenIV::getWideRecurrence(NarrowIVDefUse DU) {
/// This IV user cannot be widen. Replace this use of the original narrow IV
/// with a truncation of the new wide IV to isolate and eliminate the narrow IV.
static void truncateIVUse(NarrowIVDefUse DU, DominatorTree *DT, LoopInfo *LI) {
auto *InsertPt = getInsertPointForUses(DU.NarrowUse, DU.NarrowDef, DT, LI);
if (!InsertPt)
return;
LLVM_DEBUG(dbgs() << "INDVARS: Truncate IV " << *DU.WideDef << " for user "
<< *DU.NarrowUse << "\n");
IRBuilder<> Builder(
getInsertPointForUses(DU.NarrowUse, DU.NarrowDef, DT, LI));
IRBuilder<> Builder(InsertPt);
Value *Trunc = Builder.CreateTrunc(DU.WideDef, DU.NarrowDef->getType());
DU.NarrowUse->replaceUsesOfWith(DU.NarrowDef, Trunc);
}
@ -1347,8 +1359,10 @@ bool WidenIV::widenLoopCompare(NarrowIVDefUse DU) {
assert(CastWidth <= IVWidth && "Unexpected width while widening compare.");
// Widen the compare instruction.
IRBuilder<> Builder(
getInsertPointForUses(DU.NarrowUse, DU.NarrowDef, DT, LI));
auto *InsertPt = getInsertPointForUses(DU.NarrowUse, DU.NarrowDef, DT, LI);
if (!InsertPt)
return false;
IRBuilder<> Builder(InsertPt);
DU.NarrowUse->replaceUsesOfWith(DU.NarrowDef, DU.WideDef);
// Widen the other operand of the compare, if necessary.

27
llvm/test/Transforms/IndVarSimplify/pr40454.ll
View File

@ -1,11 +1,32 @@
; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
; RUN: opt -S -indvars < %s | FileCheck %s
; REQUIRES: asserts
; XFAIL: *
target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
define void @test() {
; CHECK-LABEL: @test
; CHECK-LABEL: @test(
; CHECK-NEXT: bb:
; CHECK-NEXT: br label [[BB2:%.*]]
; CHECK: bb1:
; CHECK-NEXT: br label [[BB2]]
; CHECK: bb2:
; CHECK-NEXT: [[TMP:%.*]] = phi i32 [ -9, [[BB:%.*]] ], [ [[TMP6:%.*]], [[BB1:%.*]] ]
; CHECK-NEXT: br label [[BB3:%.*]]
; CHECK: bb3:
; CHECK-NEXT: [[TMP4:%.*]] = phi i32 [ -9, [[BB2]] ], [ [[TMP6]], [[BB10:%.*]] ]
; CHECK-NEXT: br i1 false, label [[BB5:%.*]], label [[BB12:%.*]]
; CHECK: bb5:
; CHECK-NEXT: [[TMP6]] = add nsw i32 [[TMP4]], -1
; CHECK-NEXT: br i1 undef, label [[BB8:%.*]], label [[BB9:%.*]]
; CHECK: bb8:
; CHECK-NEXT: br label [[BB10]]
; CHECK: bb9:
; CHECK-NEXT: br label [[BB10]]
; CHECK: bb10:
; CHECK-NEXT: br label [[BB3]]
; CHECK: bb12:
; CHECK-NEXT: ret void
;
bb:
br label %bb2