[llvm] [clang-tools-extra] [LoopConstrainer] Apply loop gurads to check that loop bounds are safe (PR #71531)
Aleksandr Popov via llvm-commits
llvm-commits at lists.llvm.org
Thu Jan 18 13:34:58 PST 2024
https://github.com/aleks-tmb updated https://github.com/llvm/llvm-project/pull/71531
>From c734c948599ace737d48b32a817bd6410bd2b13e Mon Sep 17 00:00:00 2001
From: Aleksander Popov <apopov at azul.com>
Date: Tue, 7 Nov 2023 05:31:13 +0100
Subject: [PATCH] [LoopConstrainer] Apply loop gurads to check that loop bounds
are safe
Loop guards that apply to loop SCEV bounds allow IRCE for cases with
compound loop bounds such as:
if (K > 0 && M > 0)
for (i = 0; i < min(K, M); i++) {...}
if (K > 0 && M > 0)
for (i = min(K, M); i >= 0; i--) {...}
Otherwise SCEV couldn't prove that loops have safe bounds in these
cases.
---
llvm/lib/Transforms/Utils/LoopConstrainer.cpp | 22 +++--
.../Transforms/IRCE/compound-loop-bound.ll | 85 +++++++++++++++++--
2 files changed, 90 insertions(+), 17 deletions(-)
diff --git a/llvm/lib/Transforms/Utils/LoopConstrainer.cpp b/llvm/lib/Transforms/Utils/LoopConstrainer.cpp
index ea6d952cfa7d4f..da6f37df5b314a 100644
--- a/llvm/lib/Transforms/Utils/LoopConstrainer.cpp
+++ b/llvm/lib/Transforms/Utils/LoopConstrainer.cpp
@@ -42,8 +42,11 @@ static bool isSafeDecreasingBound(const SCEV *Start, const SCEV *BoundSCEV,
ICmpInst::Predicate BoundPred =
IsSigned ? CmpInst::ICMP_SGT : CmpInst::ICMP_UGT;
+ auto StartLG = SE.applyLoopGuards(Start, L);
+ auto BoundLG = SE.applyLoopGuards(BoundSCEV, L);
+
if (LatchBrExitIdx == 1)
- return SE.isLoopEntryGuardedByCond(L, BoundPred, Start, BoundSCEV);
+ return SE.isLoopEntryGuardedByCond(L, BoundPred, StartLG, BoundLG);
assert(LatchBrExitIdx == 0 && "LatchBrExitIdx should be either 0 or 1");
@@ -54,10 +57,10 @@ static bool isSafeDecreasingBound(const SCEV *Start, const SCEV *BoundSCEV,
const SCEV *Limit = SE.getMinusSCEV(SE.getConstant(Min), StepPlusOne);
const SCEV *MinusOne =
- SE.getMinusSCEV(BoundSCEV, SE.getOne(BoundSCEV->getType()));
+ SE.getMinusSCEV(BoundLG, SE.getOne(BoundLG->getType()));
- return SE.isLoopEntryGuardedByCond(L, BoundPred, Start, MinusOne) &&
- SE.isLoopEntryGuardedByCond(L, BoundPred, BoundSCEV, Limit);
+ return SE.isLoopEntryGuardedByCond(L, BoundPred, StartLG, MinusOne) &&
+ SE.isLoopEntryGuardedByCond(L, BoundPred, BoundLG, Limit);
}
/// Given a loop with an increasing induction variable, is it possible to
@@ -86,8 +89,11 @@ static bool isSafeIncreasingBound(const SCEV *Start, const SCEV *BoundSCEV,
ICmpInst::Predicate BoundPred =
IsSigned ? CmpInst::ICMP_SLT : CmpInst::ICMP_ULT;
+ auto StartLG = SE.applyLoopGuards(Start, L);
+ auto BoundLG = SE.applyLoopGuards(BoundSCEV, L);
+
if (LatchBrExitIdx == 1)
- return SE.isLoopEntryGuardedByCond(L, BoundPred, Start, BoundSCEV);
+ return SE.isLoopEntryGuardedByCond(L, BoundPred, StartLG, BoundLG);
assert(LatchBrExitIdx == 0 && "LatchBrExitIdx should be 0 or 1");
@@ -97,9 +103,9 @@ static bool isSafeIncreasingBound(const SCEV *Start, const SCEV *BoundSCEV,
: APInt::getMaxValue(BitWidth);
const SCEV *Limit = SE.getMinusSCEV(SE.getConstant(Max), StepMinusOne);
- return (SE.isLoopEntryGuardedByCond(L, BoundPred, Start,
- SE.getAddExpr(BoundSCEV, Step)) &&
- SE.isLoopEntryGuardedByCond(L, BoundPred, BoundSCEV, Limit));
+ return (SE.isLoopEntryGuardedByCond(L, BoundPred, StartLG,
+ SE.getAddExpr(BoundLG, Step)) &&
+ SE.isLoopEntryGuardedByCond(L, BoundPred, BoundLG, Limit));
}
/// Returns estimate for max latch taken count of the loop of the narrowest
diff --git a/llvm/test/Transforms/IRCE/compound-loop-bound.ll b/llvm/test/Transforms/IRCE/compound-loop-bound.ll
index 0930d19e22154f..e50d8c6127f401 100644
--- a/llvm/test/Transforms/IRCE/compound-loop-bound.ll
+++ b/llvm/test/Transforms/IRCE/compound-loop-bound.ll
@@ -16,23 +16,56 @@ define void @incrementing_loop(ptr %arr, ptr %len_ptr, i32 %K, i32 %M) {
; CHECK-NEXT: br i1 [[AND]], label [[PREHEADER:%.*]], label [[EXIT:%.*]]
; CHECK: preheader:
; CHECK-NEXT: [[SMIN:%.*]] = call i32 @llvm.smin.i32(i32 [[K]], i32 [[M]])
+; CHECK-NEXT: [[SMIN1:%.*]] = call i32 @llvm.smin.i32(i32 [[LEN]], i32 [[M]])
+; CHECK-NEXT: [[SMIN2:%.*]] = call i32 @llvm.smin.i32(i32 [[SMIN1]], i32 [[K]])
+; CHECK-NEXT: [[EXIT_MAINLOOP_AT:%.*]] = call i32 @llvm.smax.i32(i32 [[SMIN2]], i32 0)
+; CHECK-NEXT: [[TMP0:%.*]] = icmp slt i32 0, [[EXIT_MAINLOOP_AT]]
+; CHECK-NEXT: br i1 [[TMP0]], label [[LOOP_PREHEADER:%.*]], label [[MAIN_PSEUDO_EXIT:%.*]]
+; CHECK: loop.preheader:
; CHECK-NEXT: br label [[LOOP:%.*]]
; CHECK: loop:
-; CHECK-NEXT: [[IDX:%.*]] = phi i32 [ 0, [[PREHEADER]] ], [ [[IDX_NEXT:%.*]], [[IN_BOUNDS:%.*]] ]
-; CHECK-NEXT: [[IDX_NEXT]] = add i32 [[IDX]], 1
+; CHECK-NEXT: [[IDX:%.*]] = phi i32 [ [[IDX_NEXT:%.*]], [[IN_BOUNDS:%.*]] ], [ 0, [[LOOP_PREHEADER]] ]
+; CHECK-NEXT: [[IDX_NEXT]] = add nsw i32 [[IDX]], 1
; CHECK-NEXT: [[GUARD:%.*]] = icmp slt i32 [[IDX]], [[LEN]]
-; CHECK-NEXT: br i1 [[GUARD]], label [[IN_BOUNDS]], label [[OUT_OF_BOUNDS:%.*]]
+; CHECK-NEXT: br i1 true, label [[IN_BOUNDS]], label [[OUT_OF_BOUNDS_LOOPEXIT3:%.*]]
; CHECK: in.bounds:
; CHECK-NEXT: [[ADDR:%.*]] = getelementptr i32, ptr [[ARR]], i32 [[IDX]]
; CHECK-NEXT: store i32 0, ptr [[ADDR]], align 4
; CHECK-NEXT: [[NEXT:%.*]] = icmp slt i32 [[IDX_NEXT]], [[SMIN]]
-; CHECK-NEXT: br i1 [[NEXT]], label [[LOOP]], label [[EXIT_LOOPEXIT:%.*]]
+; CHECK-NEXT: [[TMP1:%.*]] = icmp slt i32 [[IDX_NEXT]], [[EXIT_MAINLOOP_AT]]
+; CHECK-NEXT: br i1 [[TMP1]], label [[LOOP]], label [[MAIN_EXIT_SELECTOR:%.*]]
+; CHECK: main.exit.selector:
+; CHECK-NEXT: [[IDX_NEXT_LCSSA:%.*]] = phi i32 [ [[IDX_NEXT]], [[IN_BOUNDS]] ]
+; CHECK-NEXT: [[TMP2:%.*]] = icmp slt i32 [[IDX_NEXT_LCSSA]], [[SMIN]]
+; CHECK-NEXT: br i1 [[TMP2]], label [[MAIN_PSEUDO_EXIT]], label [[EXIT_LOOPEXIT:%.*]]
+; CHECK: main.pseudo.exit:
+; CHECK-NEXT: [[IDX_COPY:%.*]] = phi i32 [ 0, [[PREHEADER]] ], [ [[IDX_NEXT_LCSSA]], [[MAIN_EXIT_SELECTOR]] ]
+; CHECK-NEXT: [[INDVAR_END:%.*]] = phi i32 [ 0, [[PREHEADER]] ], [ [[IDX_NEXT_LCSSA]], [[MAIN_EXIT_SELECTOR]] ]
+; CHECK-NEXT: br label [[POSTLOOP:%.*]]
+; CHECK: out.of.bounds.loopexit:
+; CHECK-NEXT: br label [[OUT_OF_BOUNDS:%.*]]
+; CHECK: out.of.bounds.loopexit3:
+; CHECK-NEXT: br label [[OUT_OF_BOUNDS]]
; CHECK: out.of.bounds:
; CHECK-NEXT: ret void
+; CHECK: exit.loopexit.loopexit:
+; CHECK-NEXT: br label [[EXIT_LOOPEXIT]]
; CHECK: exit.loopexit:
; CHECK-NEXT: br label [[EXIT]]
; CHECK: exit:
; CHECK-NEXT: ret void
+; CHECK: postloop:
+; CHECK-NEXT: br label [[LOOP_POSTLOOP:%.*]]
+; CHECK: loop.postloop:
+; CHECK-NEXT: [[IDX_POSTLOOP:%.*]] = phi i32 [ [[IDX_COPY]], [[POSTLOOP]] ], [ [[IDX_NEXT_POSTLOOP:%.*]], [[IN_BOUNDS_POSTLOOP:%.*]] ]
+; CHECK-NEXT: [[IDX_NEXT_POSTLOOP]] = add i32 [[IDX_POSTLOOP]], 1
+; CHECK-NEXT: [[GUARD_POSTLOOP:%.*]] = icmp slt i32 [[IDX_POSTLOOP]], [[LEN]]
+; CHECK-NEXT: br i1 [[GUARD_POSTLOOP]], label [[IN_BOUNDS_POSTLOOP]], label [[OUT_OF_BOUNDS_LOOPEXIT:%.*]]
+; CHECK: in.bounds.postloop:
+; CHECK-NEXT: [[ADDR_POSTLOOP:%.*]] = getelementptr i32, ptr [[ARR]], i32 [[IDX_POSTLOOP]]
+; CHECK-NEXT: store i32 0, ptr [[ADDR_POSTLOOP]], align 4
+; CHECK-NEXT: [[NEXT_POSTLOOP:%.*]] = icmp slt i32 [[IDX_NEXT_POSTLOOP]], [[SMIN]]
+; CHECK-NEXT: br i1 [[NEXT_POSTLOOP]], label [[LOOP_POSTLOOP]], label [[EXIT_LOOPEXIT_LOOPEXIT:%.*]], !llvm.loop [[LOOP1:![0-9]+]], !loop_constrainer.loop.clone !6
;
entry:
%len = load i32, ptr %len_ptr, !range !0
@@ -78,24 +111,58 @@ define void @decrementing_loop(ptr %arr, ptr %len_ptr, i32 %K, i32 %M) {
; CHECK-NEXT: [[AND:%.*]] = and i1 [[CHECK0]], [[CHECK1]]
; CHECK-NEXT: br i1 [[AND]], label [[PREHEADER:%.*]], label [[EXIT:%.*]]
; CHECK: preheader:
-; CHECK-NEXT: [[SMIN:%.*]] = call i32 @llvm.smin.i32(i32 [[K]], i32 [[M]])
+; CHECK-NEXT: [[INDVAR_START:%.*]] = call i32 @llvm.smin.i32(i32 [[K]], i32 [[M]])
+; CHECK-NEXT: [[TMP0:%.*]] = add i32 [[INDVAR_START]], 1
+; CHECK-NEXT: [[SMIN:%.*]] = call i32 @llvm.smin.i32(i32 [[LEN]], i32 [[TMP0]])
+; CHECK-NEXT: [[SMAX:%.*]] = call i32 @llvm.smax.i32(i32 [[SMIN]], i32 0)
+; CHECK-NEXT: [[EXIT_PRELOOP_AT:%.*]] = add nsw i32 [[SMAX]], -1
+; CHECK-NEXT: [[TMP1:%.*]] = icmp sgt i32 [[INDVAR_START]], [[EXIT_PRELOOP_AT]]
+; CHECK-NEXT: br i1 [[TMP1]], label [[LOOP_PRELOOP_PREHEADER:%.*]], label [[PRELOOP_PSEUDO_EXIT:%.*]]
+; CHECK: loop.preloop.preheader:
+; CHECK-NEXT: br label [[LOOP_PRELOOP:%.*]]
+; CHECK: mainloop:
; CHECK-NEXT: br label [[LOOP:%.*]]
; CHECK: loop:
-; CHECK-NEXT: [[IDX:%.*]] = phi i32 [ [[SMIN]], [[PREHEADER]] ], [ [[IDX_DEC:%.*]], [[IN_BOUNDS:%.*]] ]
-; CHECK-NEXT: [[IDX_DEC]] = sub i32 [[IDX]], 1
+; CHECK-NEXT: [[IDX:%.*]] = phi i32 [ [[IDX_PRELOOP_COPY:%.*]], [[MAINLOOP:%.*]] ], [ [[IDX_DEC:%.*]], [[IN_BOUNDS:%.*]] ]
+; CHECK-NEXT: [[IDX_DEC]] = sub nsw i32 [[IDX]], 1
; CHECK-NEXT: [[GUARD:%.*]] = icmp slt i32 [[IDX]], [[LEN]]
-; CHECK-NEXT: br i1 [[GUARD]], label [[IN_BOUNDS]], label [[OUT_OF_BOUNDS:%.*]]
+; CHECK-NEXT: br i1 true, label [[IN_BOUNDS]], label [[OUT_OF_BOUNDS_LOOPEXIT1:%.*]]
; CHECK: in.bounds:
; CHECK-NEXT: [[ADDR:%.*]] = getelementptr i32, ptr [[ARR]], i32 [[IDX]]
; CHECK-NEXT: store i32 0, ptr [[ADDR]], align 4
; CHECK-NEXT: [[NEXT:%.*]] = icmp sgt i32 [[IDX_DEC]], -1
-; CHECK-NEXT: br i1 [[NEXT]], label [[LOOP]], label [[EXIT_LOOPEXIT:%.*]]
+; CHECK-NEXT: br i1 [[NEXT]], label [[LOOP]], label [[EXIT_LOOPEXIT_LOOPEXIT:%.*]]
+; CHECK: out.of.bounds.loopexit:
+; CHECK-NEXT: br label [[OUT_OF_BOUNDS:%.*]]
+; CHECK: out.of.bounds.loopexit1:
+; CHECK-NEXT: br label [[OUT_OF_BOUNDS]]
; CHECK: out.of.bounds:
; CHECK-NEXT: ret void
+; CHECK: exit.loopexit.loopexit:
+; CHECK-NEXT: br label [[EXIT_LOOPEXIT:%.*]]
; CHECK: exit.loopexit:
; CHECK-NEXT: br label [[EXIT]]
; CHECK: exit:
; CHECK-NEXT: ret void
+; CHECK: loop.preloop:
+; CHECK-NEXT: [[IDX_PRELOOP:%.*]] = phi i32 [ [[IDX_DEC_PRELOOP:%.*]], [[IN_BOUNDS_PRELOOP:%.*]] ], [ [[INDVAR_START]], [[LOOP_PRELOOP_PREHEADER]] ]
+; CHECK-NEXT: [[IDX_DEC_PRELOOP]] = sub i32 [[IDX_PRELOOP]], 1
+; CHECK-NEXT: [[GUARD_PRELOOP:%.*]] = icmp slt i32 [[IDX_PRELOOP]], [[LEN]]
+; CHECK-NEXT: br i1 [[GUARD_PRELOOP]], label [[IN_BOUNDS_PRELOOP]], label [[OUT_OF_BOUNDS_LOOPEXIT:%.*]]
+; CHECK: in.bounds.preloop:
+; CHECK-NEXT: [[ADDR_PRELOOP:%.*]] = getelementptr i32, ptr [[ARR]], i32 [[IDX_PRELOOP]]
+; CHECK-NEXT: store i32 0, ptr [[ADDR_PRELOOP]], align 4
+; CHECK-NEXT: [[NEXT_PRELOOP:%.*]] = icmp sgt i32 [[IDX_DEC_PRELOOP]], -1
+; CHECK-NEXT: [[TMP2:%.*]] = icmp sgt i32 [[IDX_DEC_PRELOOP]], [[EXIT_PRELOOP_AT]]
+; CHECK-NEXT: br i1 [[TMP2]], label [[LOOP_PRELOOP]], label [[PRELOOP_EXIT_SELECTOR:%.*]], !llvm.loop [[LOOP7:![0-9]+]], !loop_constrainer.loop.clone !6
+; CHECK: preloop.exit.selector:
+; CHECK-NEXT: [[IDX_DEC_PRELOOP_LCSSA:%.*]] = phi i32 [ [[IDX_DEC_PRELOOP]], [[IN_BOUNDS_PRELOOP]] ]
+; CHECK-NEXT: [[TMP3:%.*]] = icmp sgt i32 [[IDX_DEC_PRELOOP_LCSSA]], -1
+; CHECK-NEXT: br i1 [[TMP3]], label [[PRELOOP_PSEUDO_EXIT]], label [[EXIT_LOOPEXIT]]
+; CHECK: preloop.pseudo.exit:
+; CHECK-NEXT: [[IDX_PRELOOP_COPY]] = phi i32 [ [[INDVAR_START]], [[PREHEADER]] ], [ [[IDX_DEC_PRELOOP_LCSSA]], [[PRELOOP_EXIT_SELECTOR]] ]
+; CHECK-NEXT: [[INDVAR_END:%.*]] = phi i32 [ [[INDVAR_START]], [[PREHEADER]] ], [ [[IDX_DEC_PRELOOP_LCSSA]], [[PRELOOP_EXIT_SELECTOR]] ]
+; CHECK-NEXT: br label [[MAINLOOP]]
;
entry:
%len = load i32, ptr %len_ptr, !range !0
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