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Revert "[IndVars] Smart hard uses detection"

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This reverts commit 2f425e9c7946b9d74e64ebbfa33c1caa36914402.

It seems that the check that we still should do the transform if we
know the result is constant is missing in this code. So the logic that
has been deleted by this change is still sometimes accidentally useful.
I revert the change to see what can be done about it. The motivating
case is the following:

@Y = global [400 x i16] zeroinitializer, align 1

define i16 @foo() {
entry:
  br label %for.body

for.body:                                         ; preds = %entry, %for.body
  %i = phi i16 [ 0, %entry ], [ %inc, %for.body ]

  %arrayidx = getelementptr inbounds [400 x i16], [400 x i16]* @Y, i16 0, i16 %i
  store i16 0, i16* %arrayidx, align 1
  %inc = add nuw nsw i16 %i, 1
  %cmp = icmp ult i16 %inc, 400
  br i1 %cmp, label %for.body, label %for.end

for.end:                                          ; preds = %for.body
  %inc.lcssa = phi i16 [ %inc, %for.body ]
  ret i16 %inc.lcssa
}

We should be able to figure out that the result is constant, but the patch
breaks it.

Differential Revision: https://reviews.llvm.org/D51584

llvm-svn: 346198
This commit is contained in:
Max Kazantsev 2018-11-06 02:02:05 +00:00
parent 1e6646c3db
commit fedead4684
4 changed files with 16 additions and 118 deletions
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39
lib/Transforms/Scalar/IndVarSimplify.cpp
View File

@ -145,7 +145,6 @@ class IndVarSimplify {
bool canLoopBeDeleted(Loop *L, SmallVector<RewritePhi, 8> &RewritePhiSet);
bool rewriteLoopExitValues(Loop *L, SCEVExpander &Rewriter);
bool rewriteFirstIterationLoopExitValues(Loop *L);
bool hasHardUserWithinLoop(const Loop *L, const Instruction *I) const;
bool linearFunctionTestReplace(Loop *L, const SCEV *BackedgeTakenCount,
PHINode *IndVar, SCEVExpander &Rewriter);
@ -525,29 +524,6 @@ struct RewritePhi {
// As a side effect, reduces the amount of IV processing within the loop.
//===----------------------------------------------------------------------===//
bool IndVarSimplify::hasHardUserWithinLoop(const Loop *L, const Instruction *I) const {
SmallPtrSet<const Instruction *, 8> Visited;
SmallVector<const Instruction *, 8> WorkList;
Visited.insert(I);
WorkList.push_back(I);
while (!WorkList.empty()) {
const Instruction *Curr = WorkList.pop_back_val();
// This use is outside the loop, nothing to do.
if (!L->contains(Curr))
continue;
// Do we assume it is a "hard" use which will not be eliminated easily?
if (Curr->mayHaveSideEffects())
return true;
// Otherwise, add all its users to worklist.
for (auto U : Curr->users()) {
auto *UI = cast<Instruction>(U);
if (Visited.insert(UI).second)
WorkList.push_back(UI);
}
}
return false;
}
/// Check to see if this loop has a computable loop-invariant execution count.
/// If so, this means that we can compute the final value of any expressions
/// that are recurrent in the loop, and substitute the exit values from the loop
@ -622,8 +598,19 @@ bool IndVarSimplify::rewriteLoopExitValues(Loop *L, SCEVExpander &Rewriter) {
// Computing the value outside of the loop brings no benefit if it is
// definitely used inside the loop in a way which can not be optimized
// away.
if (hasHardUserWithinLoop(L, Inst))
continue;
if (ExitValue->getSCEVType()>=scMulExpr) {
bool HasHardInternalUses = false;
for (auto *IB : Inst->users()) {
Instruction *UseInstr = cast<Instruction>(IB);
unsigned Opc = UseInstr->getOpcode();
if (L->contains(UseInstr) && Opc == Instruction::Call) {
HasHardInternalUses = true;
break;
}
}
if (HasHardInternalUses)
continue;
}
bool HighCost = Rewriter.isHighCostExpansion(ExitValue, L, Inst);
Value *ExitVal = Rewriter.expandCodeFor(ExitValue, PN->getType(), Inst);

6
test/Analysis/ScalarEvolution/pr28705.ll
View File

@ -1,11 +1,11 @@
; PR28705
; RUN: opt < %s -indvars -S | FileCheck %s
; Check IndVarSimplify doesn't replace external use of the induction var
; "%inc.i.i" with "%.sroa.speculated + 1" because it is not profitable.
; Check IndVarSimplify replaces the exitval use of the induction var "%inc.i.i"
; with "%.sroa.speculated + 1".
;
; CHECK-LABEL: @foo(
; CHECK: %[[EXIT:.+]] = phi i32 [ %inc.i.i, %for.body650 ]
; CHECK: %[[EXIT:.+]] = sub i32 %.sroa.speculated, -1
; CHECK: %DB.sroa.9.0.lcssa = phi i32 [ 1, %entry ], [ %[[EXIT]], %loopexit ]
;
define void @foo(i32 %sub.ptr.div.i, i8* %ref.i1174) local_unnamed_addr {

51
test/Transforms/IndVarSimplify/dont-recompute.ll
View File

@ -123,54 +123,3 @@ for.end: ; preds = %for.body
tail call void @func(i32 %soft_use)
ret void
}
; CHECK-LABEL: @test5(
define void @test5(i32 %m) nounwind uwtable {
entry:
br label %for.body
for.body: ; preds = %for.body, %entry
%i.06 = phi i32 [ 0, %entry ], [ %inc, %for.body ]
%a.05 = phi i32 [ 0, %entry ], [ %add, %for.body ]
%add = add i32 %a.05, %m
%soft_use = add i32 %add, 123
; CHECK: tail call void @func(i32 %soft_use)
tail call void @func(i32 %soft_use)
%inc = add nsw i32 %i.06, 1
%exitcond = icmp eq i32 %inc, 186
br i1 %exitcond, label %for.end, label %for.body
for.end: ; preds = %for.body
; CHECK: for.end:
; CHECK-NOT: mul i32 %m, 186
; CHECK:%add.lcssa = phi i32 [ %add, %for.body ]
; CHECK-NEXT: tail call void @func(i32 %add.lcssa)
tail call void @func(i32 %add)
ret void
}
; CHECK-LABEL: @test6(
define void @test6(i32 %m, i32* %p) nounwind uwtable {
entry:
br label %for.body
for.body: ; preds = %for.body, %entry
%i.06 = phi i32 [ 0, %entry ], [ %inc, %for.body ]
%a.05 = phi i32 [ 0, %entry ], [ %add, %for.body ]
%add = add i32 %a.05, %m
%soft_use = add i32 %add, 123
; CHECK: store i32 %soft_use, i32* %pidx
%pidx = getelementptr i32, i32* %p, i32 %add
store i32 %soft_use, i32* %pidx
%inc = add nsw i32 %i.06, 1
%exitcond = icmp eq i32 %inc, 186
br i1 %exitcond, label %for.end, label %for.body
for.end: ; preds = %for.body
; CHECK: for.end:
; CHECK-NOT: mul i32 %m, 186
; CHECK:%add.lcssa = phi i32 [ %add, %for.body ]
; CHECK-NEXT: tail call void @func(i32 %add.lcssa)
tail call void @func(i32 %add)
ret void
}

38
test/Transforms/IndVarSimplify/lrev-existing-umin.ll
View File

@ -1,7 +1,5 @@
; RUN: opt -S -indvars < %s | FileCheck %s
; Do not rewrite the user outside the loop because we must keep the instruction
; inside the loop due to store. Rewrite doesn't give us any profit.
define void @f(i32 %length.i.88, i32 %length.i, i8* %tmp12, i32 %tmp10, i8* %tmp8) {
; CHECK-LABEL: @f(
not_zero11.preheader:
@ -24,42 +22,6 @@ not_zero11:
%tmp23 = icmp slt i32 %tmp22, %tmp14
br i1 %tmp23, label %not_zero11, label %main.exit.selector
main.exit.selector:
; CHECK-LABEL: main.exit.selector:
; CHECK: %tmp22.lcssa = phi i32 [ %tmp22, %not_zero11 ]
; CHECK: %tmp24 = icmp slt i32 %tmp22.lcssa, %length.
%tmp24 = icmp slt i32 %tmp22, %length.i
br i1 %tmp24, label %not_zero11.postloop, label %leave
leave:
ret void
not_zero11.postloop:
ret void
}
; Rewrite the user outside the loop because there is no hard users inside the loop.
define void @f1(i32 %length.i.88, i32 %length.i, i8* %tmp12, i32 %tmp10, i8* %tmp8) {
; CHECK-LABEL: @f1(
not_zero11.preheader:
%tmp13 = icmp ugt i32 %length.i, %length.i.88
%tmp14 = select i1 %tmp13, i32 %length.i.88, i32 %length.i
%tmp15 = icmp sgt i32 %tmp14, 0
br i1 %tmp15, label %not_zero11, label %not_zero11.postloop
not_zero11:
%v_1 = phi i32 [ %tmp22, %not_zero11 ], [ 0, %not_zero11.preheader ]
%tmp16 = zext i32 %v_1 to i64
%tmp17 = getelementptr inbounds i8, i8* %tmp8, i64 %tmp16
%tmp18 = load i8, i8* %tmp17, align 1
%tmp19 = zext i8 %tmp18 to i32
%tmp20 = or i32 %tmp19, %tmp10
%tmp21 = trunc i32 %tmp20 to i8
%addr22 = getelementptr inbounds i8, i8* %tmp12, i64 %tmp16
%tmp22 = add nuw nsw i32 %v_1, 1
%tmp23 = icmp slt i32 %tmp22, %tmp14
br i1 %tmp23, label %not_zero11, label %main.exit.selector
main.exit.selector:
; CHECK-LABEL: main.exit.selector:
; CHECK: %tmp24 = icmp slt i32 %tmp14, %length.i