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clang-p2996/llvm/test/Transforms/LoopStrengthReduce/X86/sibling-loops.ll
Nikita Popov 835104a114 [LSR] Drop potentially invalid nowrap flags when switching to post-inc IV (PR46943) 
When LSR converts a branch on the pre-inc IV into a branch on the
post-inc IV, the nowrap flags on the addition may no longer be valid.
Previously, a poison result of the addition might have been ignored,
in which case the program was well defined. After branching on the
post-inc IV, we might be branching on poison, which is undefined behavior.

Fix this by discarding nowrap flags which are not present on the SCEV
expression. Nowrap flags on the SCEV expression are proven by SCEV
to always hold, independently of how the expression will be used.
This is essentially the same fix we applied to IndVars LFTR, which
also performs this kind of pre-inc to post-inc conversion.

I believe a similar problem can also exist for getelementptr inbounds,
but I was not able to come up with a problematic test case. The
inbounds case would have to be addressed in a differently anyway
(as SCEV does not track this property).

Fixes https://bugs.llvm.org/show_bug.cgi?id=46943.

Differential Revision: https://reviews.llvm.org/D95286
2021-01-25 23:13:48 +01:00

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; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
; RUN: opt -loop-reduce -S < %s | FileCheck %s
; We find it is very bad to allow LSR formula containing SCEVAddRecExpr Reg
; from siblings of current loop. When one loop is LSR optimized, it can
; insert lsr.iv for other sibling loops, which sometimes leads to many extra
; lsr.iv inserted for loops.
target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
@cond = common local_unnamed_addr global i64 0, align 8
; Check there is no extra lsr.iv generated in foo.
define void @foo(i64 %N) local_unnamed_addr {
; CHECK-LABEL: @foo(
; CHECK-NEXT: entry:
; CHECK-NEXT: br label [[DO_BODY:%.*]]
; CHECK: do.body:
; CHECK-NEXT: [[I_0:%.*]] = phi i64 [ 0, [[ENTRY:%.*]] ], [ [[INC:%.*]], [[DO_BODY]] ]
; CHECK-NEXT: tail call void @goo(i64 [[I_0]], i64 [[I_0]])
; CHECK-NEXT: [[INC]] = add nuw i64 [[I_0]], 1
; CHECK-NEXT: [[T0:%.*]] = load i64, i64* @cond, align 8
; CHECK-NEXT: [[TOBOOL:%.*]] = icmp eq i64 [[T0]], 0
; CHECK-NEXT: br i1 [[TOBOOL]], label [[DO_BODY2_PREHEADER:%.*]], label [[DO_BODY]]
; CHECK: do.body2.preheader:
; CHECK-NEXT: br label [[DO_BODY2:%.*]]
; CHECK: do.body2:
; CHECK-NEXT: [[I_1:%.*]] = phi i64 [ [[INC3:%.*]], [[DO_BODY2]] ], [ 0, [[DO_BODY2_PREHEADER]] ]
; CHECK-NEXT: [[TMP0:%.*]] = add i64 [[INC]], [[I_1]]
; CHECK-NEXT: tail call void @goo(i64 [[I_1]], i64 [[TMP0]])
; CHECK-NEXT: [[INC3]] = add nuw i64 [[I_1]], 1
; CHECK-NEXT: [[T1:%.*]] = load i64, i64* @cond, align 8
; CHECK-NEXT: [[TOBOOL6:%.*]] = icmp eq i64 [[T1]], 0
; CHECK-NEXT: br i1 [[TOBOOL6]], label [[DO_BODY8_PREHEADER:%.*]], label [[DO_BODY2]]
; CHECK: do.body8.preheader:
; CHECK-NEXT: [[TMP1:%.*]] = add i64 [[INC]], [[INC3]]
; CHECK-NEXT: br label [[DO_BODY8:%.*]]
; CHECK: do.body8:
; CHECK-NEXT: [[I_2:%.*]] = phi i64 [ [[INC9:%.*]], [[DO_BODY8]] ], [ 0, [[DO_BODY8_PREHEADER]] ]
; CHECK-NEXT: [[J_2:%.*]] = phi i64 [ [[INC10:%.*]], [[DO_BODY8]] ], [ [[TMP1]], [[DO_BODY8_PREHEADER]] ]
; CHECK-NEXT: tail call void @goo(i64 [[I_2]], i64 [[J_2]])
; CHECK-NEXT: [[INC9]] = add nuw nsw i64 [[I_2]], 1
; CHECK-NEXT: [[INC10]] = add i64 [[J_2]], 1
; CHECK-NEXT: [[T2:%.*]] = load i64, i64* @cond, align 8
; CHECK-NEXT: [[TOBOOL12:%.*]] = icmp eq i64 [[T2]], 0
; CHECK-NEXT: br i1 [[TOBOOL12]], label [[DO_BODY14_PREHEADER:%.*]], label [[DO_BODY8]]
; CHECK: do.body14.preheader:
; CHECK-NEXT: br label [[DO_BODY14:%.*]]
; CHECK: do.body14:
; CHECK-NEXT: [[I_3:%.*]] = phi i64 [ [[INC15:%.*]], [[DO_BODY14]] ], [ 0, [[DO_BODY14_PREHEADER]] ]
; CHECK-NEXT: [[J_3:%.*]] = phi i64 [ [[INC16:%.*]], [[DO_BODY14]] ], [ [[INC10]], [[DO_BODY14_PREHEADER]] ]
; CHECK-NEXT: tail call void @goo(i64 [[I_3]], i64 [[J_3]])
; CHECK-NEXT: [[INC15]] = add nuw nsw i64 [[I_3]], 1
; CHECK-NEXT: [[INC16]] = add i64 [[J_3]], 1
; CHECK-NEXT: [[T3:%.*]] = load i64, i64* @cond, align 8
; CHECK-NEXT: [[TOBOOL18:%.*]] = icmp eq i64 [[T3]], 0
; CHECK-NEXT: br i1 [[TOBOOL18]], label [[DO_BODY20_PREHEADER:%.*]], label [[DO_BODY14]]
; CHECK: do.body20.preheader:
; CHECK-NEXT: br label [[DO_BODY20:%.*]]
; CHECK: do.body20:
; CHECK-NEXT: [[I_4:%.*]] = phi i64 [ [[INC21:%.*]], [[DO_BODY20]] ], [ 0, [[DO_BODY20_PREHEADER]] ]
; CHECK-NEXT: [[J_4:%.*]] = phi i64 [ [[INC22:%.*]], [[DO_BODY20]] ], [ [[INC16]], [[DO_BODY20_PREHEADER]] ]
; CHECK-NEXT: tail call void @goo(i64 [[I_4]], i64 [[J_4]])
; CHECK-NEXT: [[INC21]] = add nuw nsw i64 [[I_4]], 1
; CHECK-NEXT: [[INC22]] = add i64 [[J_4]], 1
; CHECK-NEXT: [[T4:%.*]] = load i64, i64* @cond, align 8
; CHECK-NEXT: [[TOBOOL24:%.*]] = icmp eq i64 [[T4]], 0
; CHECK-NEXT: br i1 [[TOBOOL24]], label [[DO_BODY26_PREHEADER:%.*]], label [[DO_BODY20]]
; CHECK: do.body26.preheader:
; CHECK-NEXT: br label [[DO_BODY26:%.*]]
; CHECK: do.body26:
; CHECK-NEXT: [[I_5:%.*]] = phi i64 [ [[INC27:%.*]], [[DO_BODY26]] ], [ 0, [[DO_BODY26_PREHEADER]] ]
; CHECK-NEXT: [[J_5:%.*]] = phi i64 [ [[INC28:%.*]], [[DO_BODY26]] ], [ [[INC22]], [[DO_BODY26_PREHEADER]] ]
; CHECK-NEXT: tail call void @goo(i64 [[I_5]], i64 [[J_5]])
; CHECK-NEXT: [[INC27]] = add nuw nsw i64 [[I_5]], 1
; CHECK-NEXT: [[INC28]] = add nsw i64 [[J_5]], 1
; CHECK-NEXT: [[T5:%.*]] = load i64, i64* @cond, align 8
; CHECK-NEXT: [[TOBOOL30:%.*]] = icmp eq i64 [[T5]], 0
; CHECK-NEXT: br i1 [[TOBOOL30]], label [[DO_END31:%.*]], label [[DO_BODY26]]
; CHECK: do.end31:
; CHECK-NEXT: ret void
;
entry:
br label %do.body
do.body: ; preds = %do.body, %entry
%i.0 = phi i64 [ 0, %entry ], [ %inc, %do.body ]
tail call void @goo(i64 %i.0, i64 %i.0)
%inc = add nuw nsw i64 %i.0, 1
%t0 = load i64, i64* @cond, align 8
%tobool = icmp eq i64 %t0, 0
br i1 %tobool, label %do.body2.preheader, label %do.body
do.body2.preheader: ; preds = %do.body
br label %do.body2
do.body2: ; preds = %do.body2.preheader, %do.body2
%i.1 = phi i64 [ %inc3, %do.body2 ], [ 0, %do.body2.preheader ]
%j.1 = phi i64 [ %inc4, %do.body2 ], [ %inc, %do.body2.preheader ]
tail call void @goo(i64 %i.1, i64 %j.1)
%inc3 = add nuw nsw i64 %i.1, 1
%inc4 = add nsw i64 %j.1, 1
%t1 = load i64, i64* @cond, align 8
%tobool6 = icmp eq i64 %t1, 0
br i1 %tobool6, label %do.body8.preheader, label %do.body2
do.body8.preheader: ; preds = %do.body2
br label %do.body8
do.body8: ; preds = %do.body8.preheader, %do.body8
%i.2 = phi i64 [ %inc9, %do.body8 ], [ 0, %do.body8.preheader ]
%j.2 = phi i64 [ %inc10, %do.body8 ], [ %inc4, %do.body8.preheader ]
tail call void @goo(i64 %i.2, i64 %j.2)
%inc9 = add nuw nsw i64 %i.2, 1
%inc10 = add nsw i64 %j.2, 1
%t2 = load i64, i64* @cond, align 8
%tobool12 = icmp eq i64 %t2, 0
br i1 %tobool12, label %do.body14.preheader, label %do.body8
do.body14.preheader: ; preds = %do.body8
br label %do.body14
do.body14: ; preds = %do.body14.preheader, %do.body14
%i.3 = phi i64 [ %inc15, %do.body14 ], [ 0, %do.body14.preheader ]
%j.3 = phi i64 [ %inc16, %do.body14 ], [ %inc10, %do.body14.preheader ]
tail call void @goo(i64 %i.3, i64 %j.3)
%inc15 = add nuw nsw i64 %i.3, 1
%inc16 = add nsw i64 %j.3, 1
%t3 = load i64, i64* @cond, align 8
%tobool18 = icmp eq i64 %t3, 0
br i1 %tobool18, label %do.body20.preheader, label %do.body14
do.body20.preheader: ; preds = %do.body14
br label %do.body20
do.body20: ; preds = %do.body20.preheader, %do.body20
%i.4 = phi i64 [ %inc21, %do.body20 ], [ 0, %do.body20.preheader ]
%j.4 = phi i64 [ %inc22, %do.body20 ], [ %inc16, %do.body20.preheader ]
tail call void @goo(i64 %i.4, i64 %j.4)
%inc21 = add nuw nsw i64 %i.4, 1
%inc22 = add nsw i64 %j.4, 1
%t4 = load i64, i64* @cond, align 8
%tobool24 = icmp eq i64 %t4, 0
br i1 %tobool24, label %do.body26.preheader, label %do.body20
do.body26.preheader: ; preds = %do.body20
br label %do.body26
do.body26: ; preds = %do.body26.preheader, %do.body26
%i.5 = phi i64 [ %inc27, %do.body26 ], [ 0, %do.body26.preheader ]
%j.5 = phi i64 [ %inc28, %do.body26 ], [ %inc22, %do.body26.preheader ]
tail call void @goo(i64 %i.5, i64 %j.5)
%inc27 = add nuw nsw i64 %i.5, 1
%inc28 = add nsw i64 %j.5, 1
%t5 = load i64, i64* @cond, align 8
%tobool30 = icmp eq i64 %t5, 0
br i1 %tobool30, label %do.end31, label %do.body26
do.end31: ; preds = %do.body26
ret void
}
declare void @goo(i64, i64) local_unnamed_addr
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