[PATCH] D102635: [LoopUnroll] Use tripcount from exiting header, if latch not exiting.
Florian Hahn via Phabricator via llvm-commits
llvm-commits at lists.llvm.org
Mon May 17 09:26:51 PDT 2021
fhahn created this revision.
fhahn added reviewers: reames, Whitney, Meinersbur, mkazantsev.
Herald added subscribers: zzheng, hiraditya.
fhahn requested review of this revision.
Herald added a project: LLVM.
Currently we use the trip count from the exiting latch or from the
unique exit block. If the loop is not rotated, the latch won't exit but
the header will.
This patch falls back to using the trip count from the header, if the
header is exiting and the latch is not.
This fixes cases where we failed to unroll with -Oz, like
https://godbolt.org/z/fP6sna8qK
bool foo(int *ptr, int limit) {
#pragma clang loop unroll(full)
for (unsigned int i = 0; i < 4; i++) {
if (ptr[i] > limit)
return false;
ptr[i]++;
}
return true;
}
Repository:
rG LLVM Github Monorepo
https://reviews.llvm.org/D102635
Files:
llvm/lib/Transforms/Scalar/LoopUnrollPass.cpp
llvm/test/Transforms/LoopUnroll/unroll-header-exiting-with-phis-multiple-exiting-blocks.ll
Index: llvm/test/Transforms/LoopUnroll/unroll-header-exiting-with-phis-multiple-exiting-blocks.ll
===================================================================
--- llvm/test/Transforms/LoopUnroll/unroll-header-exiting-with-phis-multiple-exiting-blocks.ll
+++ llvm/test/Transforms/LoopUnroll/unroll-header-exiting-with-phis-multiple-exiting-blocks.ll
@@ -8,25 +8,53 @@
; CHECK-NEXT: entry:
; CHECK-NEXT: br label [[HEADER:%.*]]
; CHECK: header:
-; CHECK-NEXT: [[RES:%.*]] = phi i16 [ 123, [[ENTRY:%.*]] ], [ [[RES_NEXT:%.*]], [[LATCH:%.*]] ]
-; CHECK-NEXT: [[I_0:%.*]] = phi i64 [ 0, [[ENTRY]] ], [ [[INC9:%.*]], [[LATCH]] ]
-; CHECK-NEXT: [[PTR:%.*]] = getelementptr inbounds i16, i16* [[A:%.*]], i64 [[I_0]]
-; CHECK-NEXT: [[LV:%.*]] = load i16, i16* [[PTR]], align 2
-; CHECK-NEXT: [[RES_NEXT]] = add i16 [[RES]], [[LV]]
-; CHECK-NEXT: [[CMP:%.*]] = icmp ult i64 [[I_0]], 3
-; CHECK-NEXT: br i1 [[CMP]], label [[EXITING_1:%.*]], label [[EXIT:%.*]]
+; CHECK-NEXT: [[LV:%.*]] = load i16, i16* [[A:%.*]], align 2
+; CHECK-NEXT: [[RES_NEXT:%.*]] = add i16 123, [[LV]]
+; CHECK-NEXT: br i1 true, label [[EXITING_1:%.*]], label [[EXIT:%.*]]
; CHECK: exiting.1:
; CHECK-NEXT: [[EC_1:%.*]] = icmp eq i16 [[LV]], [[X:%.*]]
; CHECK-NEXT: br i1 [[EC_1]], label [[EXIT]], label [[EXITING_2:%.*]]
; CHECK: exiting.2:
; CHECK-NEXT: [[EC_2:%.*]] = icmp eq i16 [[LV]], [[Y:%.*]]
-; CHECK-NEXT: br i1 [[EC_2]], label [[EXIT]], label [[LATCH]]
+; CHECK-NEXT: br i1 [[EC_2]], label [[EXIT]], label [[LATCH:%.*]]
; CHECK: latch:
-; CHECK-NEXT: [[INC9]] = add i64 [[I_0]], 1
-; CHECK-NEXT: br label [[HEADER]]
+; CHECK-NEXT: [[PTR_1:%.*]] = getelementptr inbounds i16, i16* [[A]], i64 1
+; CHECK-NEXT: [[LV_1:%.*]] = load i16, i16* [[PTR_1]], align 2
+; CHECK-NEXT: [[RES_NEXT_1:%.*]] = add i16 [[RES_NEXT]], [[LV_1]]
+; CHECK-NEXT: br i1 true, label [[EXITING_1_1:%.*]], label [[EXIT]]
; CHECK: exit:
-; CHECK-NEXT: [[RES_LCSSA:%.*]] = phi i16 [ [[RES_NEXT]], [[HEADER]] ], [ 0, [[EXITING_1]] ], [ 1, [[EXITING_2]] ]
+; CHECK-NEXT: [[RES_LCSSA:%.*]] = phi i16 [ [[RES_NEXT]], [[HEADER]] ], [ 0, [[EXITING_1]] ], [ 1, [[EXITING_2]] ], [ [[RES_NEXT_1]], [[LATCH]] ], [ 0, [[EXITING_1_1]] ], [ 1, [[EXITING_2_1:%.*]] ], [ [[RES_NEXT_2:%.*]], [[LATCH_1:%.*]] ], [ 0, [[EXITING_1_2:%.*]] ], [ 1, [[EXITING_2_2:%.*]] ], [ [[RES_NEXT_3:%.*]], [[LATCH_2:%.*]] ], [ 0, [[EXITING_1_3:%.*]] ], [ 1, [[EXITING_2_3:%.*]] ]
; CHECK-NEXT: ret i16 [[RES_LCSSA]]
+; CHECK: exiting.1.1:
+; CHECK-NEXT: [[EC_1_1:%.*]] = icmp eq i16 [[LV_1]], [[X]]
+; CHECK-NEXT: br i1 [[EC_1_1]], label [[EXIT]], label [[EXITING_2_1]]
+; CHECK: exiting.2.1:
+; CHECK-NEXT: [[EC_2_1:%.*]] = icmp eq i16 [[LV_1]], [[Y]]
+; CHECK-NEXT: br i1 [[EC_2_1]], label [[EXIT]], label [[LATCH_1]]
+; CHECK: latch.1:
+; CHECK-NEXT: [[PTR_2:%.*]] = getelementptr inbounds i16, i16* [[A]], i64 2
+; CHECK-NEXT: [[LV_2:%.*]] = load i16, i16* [[PTR_2]], align 2
+; CHECK-NEXT: [[RES_NEXT_2]] = add i16 [[RES_NEXT_1]], [[LV_2]]
+; CHECK-NEXT: br i1 true, label [[EXITING_1_2]], label [[EXIT]]
+; CHECK: exiting.1.2:
+; CHECK-NEXT: [[EC_1_2:%.*]] = icmp eq i16 [[LV_2]], [[X]]
+; CHECK-NEXT: br i1 [[EC_1_2]], label [[EXIT]], label [[EXITING_2_2]]
+; CHECK: exiting.2.2:
+; CHECK-NEXT: [[EC_2_2:%.*]] = icmp eq i16 [[LV_2]], [[Y]]
+; CHECK-NEXT: br i1 [[EC_2_2]], label [[EXIT]], label [[LATCH_2]]
+; CHECK: latch.2:
+; CHECK-NEXT: [[PTR_3:%.*]] = getelementptr inbounds i16, i16* [[A]], i64 3
+; CHECK-NEXT: [[LV_3:%.*]] = load i16, i16* [[PTR_3]], align 2
+; CHECK-NEXT: [[RES_NEXT_3]] = add i16 [[RES_NEXT_2]], [[LV_3]]
+; CHECK-NEXT: br i1 false, label [[EXITING_1_3]], label [[EXIT]]
+; CHECK: exiting.1.3:
+; CHECK-NEXT: [[EC_1_3:%.*]] = icmp eq i16 [[LV_3]], [[X]]
+; CHECK-NEXT: br i1 [[EC_1_3]], label [[EXIT]], label [[EXITING_2_3]]
+; CHECK: exiting.2.3:
+; CHECK-NEXT: [[EC_2_3:%.*]] = icmp eq i16 [[LV_3]], [[Y]]
+; CHECK-NEXT: br i1 [[EC_2_3]], label [[EXIT]], label [[LATCH_3:%.*]]
+; CHECK: latch.3:
+; CHECK-NEXT: unreachable
;
entry:
br label %header
Index: llvm/lib/Transforms/Scalar/LoopUnrollPass.cpp
===================================================================
--- llvm/lib/Transforms/Scalar/LoopUnrollPass.cpp
+++ llvm/lib/Transforms/Scalar/LoopUnrollPass.cpp
@@ -1115,6 +1115,11 @@
BasicBlock *ExitingBlock = L->getLoopLatch();
if (!ExitingBlock || !L->isLoopExiting(ExitingBlock))
ExitingBlock = L->getExitingBlock();
+ // If the latch is not exiting and there's no single exiting block, check if
+ // the header is exiting and use it to estimate the trip count. This can
+ // happen when unrolling non-rotated loops.
+ if (!ExitingBlock && L->isLoopExiting(L->getHeader()))
+ ExitingBlock = L->getHeader();
if (ExitingBlock) {
TripCount = SE.getSmallConstantTripCount(L, ExitingBlock);
TripMultiple = SE.getSmallConstantTripMultiple(L, ExitingBlock);
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