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[LoopUnroll] Handle certain PHIs in full unrolling properly 

Summary:
When reconstructing the CFG of the loop after unrolling,
LoopUnroll could in some cases remove the phi operands of
loop-carried values instead of preserving them, resulting
in undef phi values after loop unrolling.

When doing this reconstruction, avoid removing incoming
phi values for phis in the successor blocks if the successor
is the block we are jumping to anyway.

Patch-by: ebevhan

Reviewers: fhahn, efriedma

Reviewed By: fhahn

Subscribers: bjope, lebedev.ri, zzheng, dmgreen, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D66334

llvm-svn: 369886
This commit is contained in:
Bjorn Pettersson 2019-08-26 09:29:53 +00:00
parent d43d912b4b
commit d804bd17de
2 changed files with 112 additions and 3 deletions
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8
llvm/lib/Transforms/Utils/LoopUnroll.cpp
View File

@ -711,7 +711,7 @@ LoopUnrollResult llvm::UnrollLoop(Loop *L, UnrollLoopOptions ULO, LoopInfo *LI,
auto setDest = [LoopExit, ContinueOnTrue](BasicBlock *Src, BasicBlock *Dest,
ArrayRef<BasicBlock *> NextBlocks,
BasicBlock *CurrentHeader,
BasicBlock *BlockInLoop,
bool NeedConditional) {
auto *Term = cast<BranchInst>(Src->getTerminator());
if (NeedConditional) {
@ -723,7 +723,9 @@ LoopUnrollResult llvm::UnrollLoop(Loop *L, UnrollLoopOptions ULO, LoopInfo *LI,
if (Dest != LoopExit) {
BasicBlock *BB = Src;
for (BasicBlock *Succ : successors(BB)) {
if (Succ == CurrentHeader)
// Preserve the incoming value from BB if we are jumping to the block
// in the current loop.
if (Succ == BlockInLoop)
continue;
for (PHINode &Phi : Succ->phis())
Phi.removeIncomingValue(BB, false);
@ -794,7 +796,7 @@ LoopUnrollResult llvm::UnrollLoop(Loop *L, UnrollLoopOptions ULO, LoopInfo *LI,
// unconditional branch for some iterations.
NeedConditional = false;
setDest(Headers[i], Dest, Headers, Headers[i], NeedConditional);
setDest(Headers[i], Dest, Headers, HeaderSucc[i], NeedConditional);
}
// Set up latches to branch to the new header in the unrolled iterations or

107
llvm/test/Transforms/LoopUnroll/unroll-header-exiting-with-phis.ll Normal file
View File

@ -0,0 +1,107 @@
; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
; RUN: opt < %s -S -loop-unroll -unroll-allow-partial | FileCheck %s
; The phi which acts as input to func should not be undef. It should
; have its loop-carried value (the load in for.cond) replaced accordingly
; after unrolling the loop.
define i16 @full_unroll(i16* %A) {
; CHECK-LABEL: @full_unroll(
; CHECK-NEXT: entry:
; CHECK-NEXT: br label [[FOR_COND:%.*]]
; CHECK: for.cond:
; CHECK-NEXT: [[TMP2:%.*]] = load i16, i16* [[A:%.*]]
; CHECK-NEXT: br label [[FOR_COND_CLEANUP3:%.*]]
; CHECK: for.cond.cleanup:
; CHECK-NEXT: [[DOTLCSSA10_LCSSA:%.*]] = phi i16 [ [[TMP2_2:%.*]], [[FOR_COND_CLEANUP3_2:%.*]] ]
; CHECK-NEXT: [[TMP3:%.*]] = call i16 @func(i16 [[DOTLCSSA10_LCSSA]])
; CHECK-NEXT: ret i16 0
; CHECK: for.cond.cleanup3:
; CHECK-NEXT: [[PTR_1:%.*]] = getelementptr inbounds i16, i16* [[A]], i64 1
; CHECK-NEXT: [[TMP2_1:%.*]] = load i16, i16* [[PTR_1]]
; CHECK-NEXT: br label [[FOR_COND_CLEANUP3_1:%.*]]
; CHECK: for.cond.cleanup3.1:
; CHECK-NEXT: [[PTR_2:%.*]] = getelementptr inbounds i16, i16* [[A]], i64 2
; CHECK-NEXT: [[TMP2_2]] = load i16, i16* [[PTR_2]]
; CHECK-NEXT: br label [[FOR_COND_CLEANUP3_2]]
; CHECK: for.cond.cleanup3.2:
; CHECK-NEXT: [[PTR_3:%.*]] = getelementptr inbounds i16, i16* [[A]], i64 3
; CHECK-NEXT: [[TMP2_3:%.*]] = load i16, i16* [[PTR_3]]
; CHECK-NEXT: br i1 false, label [[FOR_COND_CLEANUP3_3:%.*]], label [[FOR_COND_CLEANUP:%.*]]
; CHECK: for.cond.cleanup3.3:
; CHECK-NEXT: unreachable
;
entry:
br label %for.cond
for.cond: ; preds = %for.cond.cleanup3, %entry
%.lcssa10 = phi i16 [ 123, %entry ], [ %.lcssa, %for.cond.cleanup3 ]
%i.0 = phi i64 [ 0, %entry ], [ %inc9, %for.cond.cleanup3 ]
%ptr = getelementptr inbounds i16, i16* %A, i64 %i.0
%tmp2 = load i16, i16* %ptr
%cmp = icmp ult i64 %i.0, 3
br i1 %cmp, label %for.cond.cleanup3, label %for.cond.cleanup
for.cond.cleanup: ; preds = %for.cond
%.lcssa10.lcssa = phi i16 [ %.lcssa10, %for.cond ]
%tmp3 = call i16 (i16) @func(i16 %.lcssa10.lcssa)
ret i16 0
for.cond.cleanup3: ; preds = %for.cond
%.lcssa = phi i16 [ %tmp2, %for.cond ]
%inc9 = add i64 %i.0, 1
br label %for.cond
}
define i16 @partial_unroll(i16* %A) {
; CHECK-LABEL: @partial_unroll(
; CHECK-NEXT: entry:
; CHECK-NEXT: br label [[FOR_COND:%.*]]
; CHECK: for.cond:
; CHECK-NEXT: [[I_0:%.*]] = phi i64 [ 0, [[ENTRY:%.*]] ], [ [[INC9_2:%.*]], [[FOR_COND_CLEANUP3_2:%.*]] ]
; CHECK-NEXT: [[PTR:%.*]] = getelementptr inbounds i16, i16* [[A:%.*]], i64 [[I_0]]
; CHECK-NEXT: [[TMP2:%.*]] = load i16, i16* [[PTR]]
; CHECK-NEXT: br label [[FOR_COND_CLEANUP3:%.*]]
; CHECK: for.cond.cleanup:
; CHECK-NEXT: [[DOTLCSSA10_LCSSA:%.*]] = phi i16 [ [[TMP2_1:%.*]], [[FOR_COND_CLEANUP3_1:%.*]] ]
; CHECK-NEXT: [[TMP3:%.*]] = call i16 @func(i16 [[DOTLCSSA10_LCSSA]])
; CHECK-NEXT: ret i16 0
; CHECK: for.cond.cleanup3:
; CHECK-NEXT: [[INC9:%.*]] = add nuw nsw i64 [[I_0]], 1
; CHECK-NEXT: [[PTR_1:%.*]] = getelementptr inbounds i16, i16* [[A]], i64 [[INC9]]
; CHECK-NEXT: [[TMP2_1]] = load i16, i16* [[PTR_1]]
; CHECK-NEXT: br label [[FOR_COND_CLEANUP3_1]]
; CHECK: for.cond.cleanup3.1:
; CHECK-NEXT: [[INC9_1:%.*]] = add nuw nsw i64 [[INC9]], 1
; CHECK-NEXT: [[PTR_2:%.*]] = getelementptr inbounds i16, i16* [[A]], i64 [[INC9_1]]
; CHECK-NEXT: [[TMP2_2:%.*]] = load i16, i16* [[PTR_2]]
; CHECK-NEXT: [[CMP_2:%.*]] = icmp ult i64 [[INC9_1]], 200
; CHECK-NEXT: br i1 [[CMP_2]], label [[FOR_COND_CLEANUP3_2]], label [[FOR_COND_CLEANUP:%.*]]
; CHECK: for.cond.cleanup3.2:
; CHECK-NEXT: [[INC9_2]] = add nuw nsw i64 [[INC9_1]], 1
; CHECK-NEXT: br label [[FOR_COND]]
;
entry:
br label %for.cond
for.cond: ; preds = %for.cond.cleanup3, %entry
%.lcssa10 = phi i16 [ 123, %entry ], [ %.lcssa, %for.cond.cleanup3 ]
%i.0 = phi i64 [ 0, %entry ], [ %inc9, %for.cond.cleanup3 ]
%ptr = getelementptr inbounds i16, i16* %A, i64 %i.0
%tmp2 = load i16, i16* %ptr
%cmp = icmp ult i64 %i.0, 200
br i1 %cmp, label %for.cond.cleanup3, label %for.cond.cleanup
for.cond.cleanup: ; preds = %for.cond
%.lcssa10.lcssa = phi i16 [ %.lcssa10, %for.cond ]
%tmp3 = call i16 (i16) @func(i16 %.lcssa10.lcssa)
ret i16 0
for.cond.cleanup3: ; preds = %for.cond
%.lcssa = phi i16 [ %tmp2, %for.cond ]
%inc9 = add i64 %i.0, 1
br label %for.cond
}
declare i16 @func(i16)