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[LoopPred] Be uniform about proving generated conditions 

We'd been optimizing the case where the predicate was obviously true, do the same for the false case.  Mostly just for completeness sake, but also may improve compile time in loops which will exit through the guard.  Such loops are presumed rare in fastpath code, but may be present down untaken paths, so optimizing for them is still useful.

llvm-svn: 357408
This commit is contained in:
Philip Reames 2019-04-01 16:26:08 +00:00
parent 6c21ccd245
commit 05e3e554b4
2 changed files with 52 additions and 0 deletions
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3
llvm/lib/Transforms/Scalar/LoopPredication.cpp
View File

@ -396,6 +396,9 @@ Value *LoopPredication::expandCheck(SCEVExpander &Expander,
if (SE->isLoopEntryGuardedByCond(L, Pred, LHS, RHS))
return Builder.getTrue();
if (SE->isLoopEntryGuardedByCond(L, ICmpInst::getInversePredicate(Pred),
LHS, RHS))
return Builder.getFalse();
Instruction *InsertAt = &*Builder.GetInsertPoint();
Value *LHSV = Expander.expandCodeFor(LHS, Ty, InsertAt);

49
llvm/test/Transforms/LoopPredication/basic.ll
View File

@ -1544,3 +1544,52 @@ exit:
%result = phi i32 [ 0, %entry ], [ %loop.acc.next, %loop ]
ret i32 %result
}
; This is a case where the length information tells us that the guard
; must trigger on some iteration.
define i32 @provably_taken(i32* %array, i32* %length.ptr) {
; CHECK-LABEL: @provably_taken(
; CHECK-NEXT: loop.preheader:
; CHECK-NEXT: [[LENGTH:%.*]] = load i32, i32* [[LENGTH_PTR:%.*]], !range !1
; CHECK-NEXT: [[TMP0:%.*]] = icmp ult i32 0, [[LENGTH]]
; CHECK-NEXT: [[TMP1:%.*]] = and i1 [[TMP0]], false
; CHECK-NEXT: br label [[LOOP:%.*]]
; CHECK: loop:
; CHECK-NEXT: [[LOOP_ACC:%.*]] = phi i32 [ [[LOOP_ACC_NEXT:%.*]], [[LOOP]] ], [ 0, [[LOOP_PREHEADER:%.*]] ]
; CHECK-NEXT: [[I:%.*]] = phi i32 [ [[I_NEXT:%.*]], [[LOOP]] ], [ 0, [[LOOP_PREHEADER]] ]
; CHECK-NEXT: call void (i1, ...) @llvm.experimental.guard(i1 [[TMP1]], i32 9) [ "deopt"() ]
; CHECK-NEXT: [[I_I64:%.*]] = zext i32 [[I]] to i64
; CHECK-NEXT: [[ARRAY_I_PTR:%.*]] = getelementptr inbounds i32, i32* [[ARRAY:%.*]], i64 [[I_I64]]
; CHECK-NEXT: [[ARRAY_I:%.*]] = load i32, i32* [[ARRAY_I_PTR]], align 4
; CHECK-NEXT: [[LOOP_ACC_NEXT]] = add i32 [[LOOP_ACC]], [[ARRAY_I]]
; CHECK-NEXT: [[I_NEXT]] = add nuw i32 [[I]], 1
; CHECK-NEXT: [[CONTINUE:%.*]] = icmp slt i32 [[I_NEXT]], 200
; CHECK-NEXT: br i1 [[CONTINUE]], label [[LOOP]], label [[EXIT:%.*]]
; CHECK: exit:
; CHECK-NEXT: [[RESULT:%.*]] = phi i32 [ [[LOOP_ACC_NEXT]], [[LOOP]] ]
; CHECK-NEXT: ret i32 [[RESULT]]
;
loop.preheader:
%length = load i32, i32* %length.ptr, !range !{i32 0, i32 50}
br label %loop
loop:
%loop.acc = phi i32 [ %loop.acc.next, %loop ], [ 0, %loop.preheader ]
%i = phi i32 [ %i.next, %loop ], [ 0, %loop.preheader ]
%within.bounds = icmp ult i32 %i, %length
call void (i1, ...) @llvm.experimental.guard(i1 %within.bounds, i32 9) [ "deopt"() ]
%i.i64 = zext i32 %i to i64
%array.i.ptr = getelementptr inbounds i32, i32* %array, i64 %i.i64
%array.i = load i32, i32* %array.i.ptr, align 4
%loop.acc.next = add i32 %loop.acc, %array.i
%i.next = add nuw i32 %i, 1
%continue = icmp slt i32 %i.next, 200
br i1 %continue, label %loop, label %exit
exit:
%result = phi i32 [ %loop.acc.next, %loop ]
ret i32 %result
}