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[LICM] Don't try to sink values out of loops without any exits

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There is no suitable basic block to sink instructions in loops without
exits.  The only way an instruction in a loop without exits can be used
is as an incoming value to a PHI.  In such cases, the incoming block for
the corresponding value is unreachable.

This fixes PR24013.

Differential Revision: http://reviews.llvm.org/D10903

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@241987 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
David Majnemer 2015-07-12 03:53:05 +00:00
parent 866cf31c07
commit a1b821fac9
2 changed files with 31 additions and 1 deletions
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13
lib/Transforms/Scalar/LICM.cpp
View File

@ -602,7 +602,8 @@ static bool sink(Instruction &I, const LoopInfo *LI, const DominatorTree *DT,
// PHI nodes in exit blocks due to LCSSA form. Just RAUW them with clones of
// the instruction.
while (!I.use_empty()) {
Instruction *User = I.user_back();
Value::user_iterator UI = I.user_begin();
auto *User = cast<Instruction>(*UI);
if (!DT->isReachableFromEntry(User->getParent())) {
User->replaceUsesOfWith(&I, UndefValue::get(I.getType()));
continue;
@ -610,6 +611,16 @@ static bool sink(Instruction &I, const LoopInfo *LI, const DominatorTree *DT,
// The user must be a PHI node.
PHINode *PN = cast<PHINode>(User);
// Surprisingly, instructions can be used outside of loops without any
// exits. This can only happen in PHI nodes if the incoming block is
// unreachable.
Use &U = UI.getUse();
BasicBlock *BB = PN->getIncomingBlock(U);
if (!DT->isReachableFromEntry(BB)) {
U = UndefValue::get(I.getType());
continue;
}
BasicBlock *ExitBlock = PN->getParent();
assert(ExitBlockSet.count(ExitBlock) &&
"The LCSSA PHI is not in an exit block!");

19
test/Transforms/LICM/PR24013.ll Normal file
View File

@ -0,0 +1,19 @@
; RUN: opt -licm -S < %s | FileCheck %s
define void @f(i1 zeroext %p1) {
; CHECK-LABEL: @f(
entry:
br label %lbl
lbl.loopexit: ; No predecessors!
br label %lbl
lbl: ; preds = %lbl.loopexit, %entry
%phi = phi i32 [ %conv, %lbl.loopexit ], [ undef, %entry ]
; CHECK: phi i32 [ undef, {{.*}} ], [ undef
br label %if.then.5
if.then.5: ; preds = %if.then.5, %lbl
%conv = zext i1 undef to i32
br label %if.then.5
}