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[RLEV] Pick a correct insert point when incoming instruction is itself a phi node

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This fixes https://github.com/llvm/llvm-project/issues/57336. It was exposed by a recent SCEV change, but appears to have been a long standing issue.

Note that the whole insert into the loop instead of a split exit edge is slightly contrived to begin with; it's there solely because IndVarSimplify preserves the CFG.

Differential Revision: https://reviews.llvm.org/D132571

(cherry picked from commit c37b1a5f764380f83ba08ae0cebca2b162123eb6)
This commit is contained in:
Philip Reames 2022-08-29 11:37:42 -07:00 committed by Tobias Hieta
parent 11ba13a625
commit be1669163f
2 changed files with 42 additions and 1 deletions
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5
llvm/lib/Transforms/Utils/LoopUtils.cpp
View file

@ -1394,7 +1394,10 @@ int llvm::rewriteLoopExitValues(Loop *L, LoopInfo *LI, TargetLibraryInfo *TLI,
// and next SCEV may errneously get smaller cost.
// Collect all the candidate PHINodes to be rewritten.
RewritePhiSet.emplace_back(PN, i, ExitValue, Inst, HighCost);
Instruction *InsertPt =
(isa<PHINode>(Inst) || isa<LandingPadInst>(Inst)) ?
&*Inst->getParent()->getFirstInsertionPt() : Inst;
RewritePhiSet.emplace_back(PN, i, ExitValue, InsertPt, HighCost);
}
}
}

38
llvm/test/Transforms/IndVarSimplify/rewrite-loop-exit-value.ll
View file

@ -158,4 +158,42 @@ exit:
ret i32 %phi_indvar
}
define i16 @pr57336(i16 %end, i16 %m) mustprogress {
; CHECK-LABEL: @pr57336(
; CHECK-NEXT: entry:
; CHECK-NEXT: br label [[FOR_BODY:%.*]]
; CHECK: for.body:
; CHECK-NEXT: [[INC8:%.*]] = phi i16 [ [[INC:%.*]], [[FOR_BODY]] ], [ 0, [[ENTRY:%.*]] ]
; CHECK-NEXT: [[INC]] = add nuw nsw i16 [[INC8]], 1
; CHECK-NEXT: [[MUL:%.*]] = mul nsw i16 [[INC8]], [[M:%.*]]
; CHECK-NEXT: [[CMP_NOT:%.*]] = icmp sgt i16 [[MUL]], [[END:%.*]]
; CHECK-NEXT: br i1 [[CMP_NOT]], label [[CRIT_EDGE:%.*]], label [[FOR_BODY]]
; CHECK: crit_edge:
; CHECK-NEXT: [[TMP0:%.*]] = call i16 @llvm.smax.i16(i16 [[END]], i16 -1)
; CHECK-NEXT: [[SMAX:%.*]] = add nsw i16 [[TMP0]], 1
; CHECK-NEXT: [[TMP1:%.*]] = icmp ne i16 [[SMAX]], 0
; CHECK-NEXT: [[UMIN:%.*]] = zext i1 [[TMP1]] to i16
; CHECK-NEXT: [[TMP2:%.*]] = sub nsw i16 [[SMAX]], [[UMIN]]
; CHECK-NEXT: [[UMAX:%.*]] = call i16 @llvm.umax.i16(i16 [[M]], i16 1)
; CHECK-NEXT: [[TMP3:%.*]] = udiv i16 [[TMP2]], [[UMAX]]
; CHECK-NEXT: [[TMP4:%.*]] = add i16 [[TMP3]], [[UMIN]]
; CHECK-NEXT: ret i16 [[TMP4]]
;
entry:
br label %for.body
for.body:
%inc8 = phi i16 [ %inc, %for.body ], [ 0, %entry ]
%inc137 = phi i32 [ %inc1, %for.body ], [ 0, %entry ]
%inc1 = add nsw i32 %inc137, 1
%inc = add nsw i16 %inc8, 1
%mul = mul nsw i16 %m, %inc8
%cmp.not = icmp slt i16 %end, %mul
br i1 %cmp.not, label %crit_edge, label %for.body
crit_edge:
%inc137.lcssa = phi i32 [ %inc137, %for.body ]
%conv = trunc i32 %inc137.lcssa to i16
ret i16 %conv
}