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Loop predication expand both sides of the widened condition 

This is a fix for a loop predication bug which resulted in malformed IR generation.

Loop invariant side of the widened condition is not guaranteed to be available in the preheader as is, so we need to expand it as well. See added unsigned_loop_0_to_n_hoist_length test for example.

Reviewed By: sanjoy, mkazantsev

Differential Revision: https://reviews.llvm.org/D30099

llvm-svn: 296345
This commit is contained in:
Artur Pilipenko 2017-02-27 15:44:49 +00:00
parent 0b59cf64a0
commit 0860bfc676
2 changed files with 83 additions and 6 deletions
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12
llvm/lib/Transforms/Scalar/LoopPredication.cpp
View File

@ -141,10 +141,9 @@ Optional<Value *> LoopPredication::widenICmpRangeCheck(ICmpInst *ICI,
std::swap(LHSS, RHSS);
Pred = ICmpInst::getSwappedPredicate(Pred);
}
if (!SE->isLoopInvariant(RHSS, L))
if (!SE->isLoopInvariant(RHSS, L) || !isSafeToExpand(RHSS, *SE))
return None;
Value *Bound = RHS;
const SCEVAddRecExpr *IndexAR = dyn_cast<SCEVAddRecExpr>(LHSS);
if (!IndexAR || IndexAR->getLoop() != L)
return None;
@ -176,9 +175,12 @@ Optional<Value *> LoopPredication::widenICmpRangeCheck(ICmpInst *ICI,
DEBUG(dbgs() << "NewLHSS is loop invariant and safe to expand. Expand!\n");
Value *NewLHS = Expander.expandCodeFor(NewLHSS, Bound->getType(),
Preheader->getTerminator());
return Builder.CreateICmp(Pred, NewLHS, Bound);
Type *Ty = LHS->getType();
Instruction *InsertAt = Preheader->getTerminator();
assert(Ty == RHS->getType() && "icmp operands have different types?");
Value *NewLHS = Expander.expandCodeFor(NewLHSS, Ty, InsertAt);
Value *NewRHS = Expander.expandCodeFor(RHSS, Ty, InsertAt);
return Builder.CreateICmp(Pred, NewLHS, NewRHS);
}
bool LoopPredication::widenGuardConditions(IntrinsicInst *Guard,

77
llvm/test/Transforms/LoopPredication/basic.ll
View File

@ -493,4 +493,79 @@ loop:
exit:
%result = phi i32 [ 0, %entry ], [ %loop.acc.next, %loop ]
ret i32 %result
}
}
define i32 @unsigned_loop_0_to_n_hoist_length(i32* %array, i16 %length.i16, i32 %n) {
; CHECK-LABEL: @unsigned_loop_0_to_n_hoist_length
entry:
%tmp5 = icmp eq i32 %n, 0
br i1 %tmp5, label %exit, label %loop.preheader
loop.preheader:
; CHECK: loop.preheader:
; CHECK: [[max_index:[^ ]+]] = add i32 %n, -1
; CHECK-NEXT: [[length:[^ ]+]] = zext i16 %length.i16 to i32
; CHECK-NEXT: [[wide_cond:[^ ]+]] = icmp ult i32 [[max_index]], [[length]]
; CHECK-NEXT: br label %loop
br label %loop
loop:
; CHECK: loop:
; CHECK: call void (i1, ...) @llvm.experimental.guard(i1 [[wide_cond]], i32 9) [ "deopt"() ]
%loop.acc = phi i32 [ %loop.acc.next, %loop ], [ 0, %loop.preheader ]
%i = phi i32 [ %i.next, %loop ], [ 0, %loop.preheader ]
%length = zext i16 %length.i16 to i32
%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 ult i32 %i.next, %n
br i1 %continue, label %loop, label %exit
exit:
%result = phi i32 [ 0, %entry ], [ %loop.acc.next, %loop ]
ret i32 %result
}
define i32 @unsigned_loop_0_to_n_cant_hoist_length(i32* %array, i32 %length, i32 %divider, i32 %n) {
; CHECK-LABEL: @unsigned_loop_0_to_n_cant_hoist_length
entry:
%tmp5 = icmp eq i32 %n, 0
br i1 %tmp5, label %exit, label %loop.preheader
loop.preheader:
; CHECK: loop.preheader:
; CHECK-NEXT: br label %loop
br label %loop
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: %length.udiv = udiv i32 %length, %divider
; CHECK-NEXT: %within.bounds = icmp ult i32 %i, %length.udiv
; CHECK-NEXT: call void (i1, ...) @llvm.experimental.guard(i1 %within.bounds, i32 9) [ "deopt"() ]
%loop.acc = phi i32 [ %loop.acc.next, %loop ], [ 0, %loop.preheader ]
%i = phi i32 [ %i.next, %loop ], [ 0, %loop.preheader ]
%length.udiv = udiv i32 %length, %divider
%within.bounds = icmp ult i32 %i, %length.udiv
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 ult i32 %i.next, %n
br i1 %continue, label %loop, label %exit
exit:
%result = phi i32 [ 0, %entry ], [ %loop.acc.next, %loop ]
ret i32 %result
}