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Return "[IndVars] Smart hard uses detection" 

The patch has been reverted because it ended up prohibiting propagation
of a constant to exit value. For such values, we should skip all checks
related to hard uses because propagating a constant is always profitable.

Differential Revision: https://reviews.llvm.org/D53691

llvm-svn: 346397
This commit is contained in:
Max Kazantsev 2018-11-08 11:54:35 +00:00
parent eb76d9fb71
commit 266c087b9d
4 changed files with 118 additions and 16 deletions
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39
llvm/lib/Transforms/Scalar/IndVarSimplify.cpp
View File

@ -145,6 +145,7 @@ 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);
@ -524,6 +525,29 @@ 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
@ -598,19 +622,8 @@ 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 (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;
}
if (!isa<SCEVConstant>(ExitValue) && hasHardUserWithinLoop(L, Inst))
continue;
bool HighCost = Rewriter.isHighCostExpansion(ExitValue, L, Inst);
Value *ExitVal = Rewriter.expandCodeFor(ExitValue, PN->getType(), Inst);

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

@ -1,11 +1,11 @@
; PR28705
; RUN: opt < %s -indvars -S | FileCheck %s
; Check IndVarSimplify replaces the exitval use of the induction var "%inc.i.i"
; with "%.sroa.speculated + 1".
; Check IndVarSimplify doesn't replace external use of the induction var
; "%inc.i.i" with "%.sroa.speculated + 1" because it is not profitable.
;
; CHECK-LABEL: @foo(
; CHECK: %[[EXIT:.+]] = sub i32 %.sroa.speculated, -1
; CHECK: %[[EXIT:.+]] = phi i32 [ %inc.i.i, %for.body650 ]
; 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
llvm/test/Transforms/IndVarSimplify/dont-recompute.ll
View File

@ -123,3 +123,54 @@ 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
llvm/test/Transforms/IndVarSimplify/lrev-existing-umin.ll
View File

@ -1,5 +1,7 @@
; 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:
@ -22,6 +24,42 @@ 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