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[LoopInterchange] Do not interchange loops with function calls.
Summary: Without any information about the called function, we cannot be sure that it is safe to interchange loops which contain function calls. For example there could be dependences that prevent interchanging between accesses in the called function and the loops. Even functions without any parameters could cause problems, as they could access memory using global pointers. For now, I think it is only safe to interchange loops with calls marked as readnone. With this patch, the LLVM test suite passes with `-O3 -mllvm -enable-loopinterchange` and LoopInterchangeProfitability::isProfitable returning true for all loops. check-llvm and check-clang also pass when bootstrapped in a similar fashion, although only 3 loops got interchanged. Reviewers: karthikthecool, blitz.opensource, hfinkel, mcrosier, mkuper Reviewed By: mcrosier Subscribers: mzolotukhin, llvm-commits Differential Revision: https://reviews.llvm.org/D35489 llvm-svn: 309547
This commit is contained in:
Florian Hahn
parent
c243f50073
commit
e48aac838f
@ -958,6 +958,18 @@ bool LoopInterchangeLegality::canInterchangeLoops(unsigned InnerLoopId,
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return false;
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}
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// Check if outer and inner loop contain legal instructions only.
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for (auto *BB : OuterLoop->blocks())
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for (Instruction &I : *BB)
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if (CallInst *CI = dyn_cast<CallInst>(&I)) {
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// readnone functions do not prevent interchanging.
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if (CI->doesNotReadMemory())
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continue;
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DEBUG(dbgs() << "Loops with call instructions cannot be interchanged "
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<< "safely.");
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return false;
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}
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// Create unique Preheaders if we already do not have one.
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BasicBlock *OuterLoopPreHeader = OuterLoop->getLoopPreheader();
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BasicBlock *InnerLoopPreHeader = InnerLoop->getLoopPreheader();
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158
test/Transforms/LoopInterchange/call-instructions.ll
Normal file
158
test/Transforms/LoopInterchange/call-instructions.ll
Normal file
@ -0,0 +1,158 @@
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; RUN: opt < %s -basicaa -loop-interchange -S | FileCheck %s
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;; We test the complete .ll for adjustment in outer loop header/latch and inner loop header/latch.
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target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
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target triple = "x86_64-unknown-linux-gnu"
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@A = common global [100 x [100 x i32]] zeroinitializer
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declare void @foo(i64 %a)
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declare void @bar(i64 %a) readnone
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;;--------------------------------------Test case 01------------------------------------
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;; Not safe to interchange, because the called function `foo` is not marked as
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;; readnone, so it could introduce dependences.
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;;
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;; for(int i=0;i<N;i++) {
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;; for(int j=1;j<N;j++) {
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;; foo(i);
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;; A[j][i] = A[j][i]+k;
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;; }
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;; }
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define void @interchange_01(i32 %k, i32 %N) {
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entry:
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%cmp21 = icmp sgt i32 %N, 0
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br i1 %cmp21, label %for1.ph, label %exit
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for1.ph:
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%cmp219 = icmp sgt i32 %N, 1
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%0 = add i32 %N, -1
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br label %for1.header
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for1.header:
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%indvars.iv23 = phi i64 [ 0, %for1.ph ], [ %indvars.iv.next24, %for1.inc10 ]
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br i1 %cmp219, label %for2.ph, label %for1.inc10
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for2.ph:
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br label %for2
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for2:
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%indvars.iv = phi i64 [ %indvars.iv.next, %for2 ], [ 1, %for2.ph ]
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call void @foo(i64 %indvars.iv23)
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%arrayidx5 = getelementptr inbounds [100 x [100 x i32]], [100 x [100 x i32]]* @A, i64 0, i64 %indvars.iv, i64 %indvars.iv23
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%1 = load i32, i32* %arrayidx5
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%add = add nsw i32 %1, %k
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store i32 %add, i32* %arrayidx5
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%indvars.iv.next = add nuw nsw i64 %indvars.iv, 1
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%lftr.wideiv = trunc i64 %indvars.iv to i32
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%exitcond = icmp eq i32 %lftr.wideiv, %0
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br i1 %exitcond, label %for2.loopexit , label %for2
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for2.loopexit:
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br label %for1.inc10
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for1.inc10:
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%indvars.iv.next24 = add nuw nsw i64 %indvars.iv23, 1
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%lftr.wideiv25 = trunc i64 %indvars.iv23 to i32
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%exitcond26 = icmp eq i32 %lftr.wideiv25, %0
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br i1 %exitcond26, label %for1.loopexit, label %for1.header
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for1.loopexit:
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br label %exit
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exit:
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ret void
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}
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; CHECK-LABEL: @interchange_01
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; CHECK: for1.ph:
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; CHECK: br label %for1.header
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; CHECK: for1.header:
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; CHECK-NEXT: %indvars.iv23 = phi i64 [ 0, %for1.ph ], [ %indvars.iv.next24, %for1.inc10 ]
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; CHECK-NEXT: br i1 %cmp219, label %for2.ph, label %for1.inc10
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; CHECK: for2:
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; CHECK: br i1 %exitcond, label %for2.loopexit, label %for2
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; CHECK: for1.inc10:
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; CHECK: br i1 %exitcond26, label %for1.loopexit, label %for1.header
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; CHECK: for1.loopexit:
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; CHECK-NEXT: br label %exit
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;;--------------------------------------Test case 02------------------------------------
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;; Safe to interchange, because the called function `bar` is marked as readnone,
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;; so it cannot introduce dependences.
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;;
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;; for(int i=0;i<N;i++) {
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;; for(int j=1;j<N;j++) {
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;; bar(i);
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;; A[j][i] = A[j][i]+k;
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;; }
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;; }
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define void @interchange_02(i32 %k, i32 %N) {
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entry:
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%cmp21 = icmp sgt i32 %N, 0
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br i1 %cmp21, label %for1.ph, label %exit
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for1.ph:
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%cmp219 = icmp sgt i32 %N, 1
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%0 = add i32 %N, -1
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br label %for1.header
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for1.header:
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%indvars.iv23 = phi i64 [ 0, %for1.ph ], [ %indvars.iv.next24, %for1.inc10 ]
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br i1 %cmp219, label %for2.ph, label %for1.inc10
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for2.ph:
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br label %for2
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for2:
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%indvars.iv = phi i64 [ %indvars.iv.next, %for2 ], [ 1, %for2.ph ]
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call void @bar(i64 %indvars.iv23)
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%arrayidx5 = getelementptr inbounds [100 x [100 x i32]], [100 x [100 x i32]]* @A, i64 0, i64 %indvars.iv, i64 %indvars.iv23
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%1 = load i32, i32* %arrayidx5
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%add = add nsw i32 %1, %k
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store i32 %add, i32* %arrayidx5
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%indvars.iv.next = add nuw nsw i64 %indvars.iv, 1
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%lftr.wideiv = trunc i64 %indvars.iv to i32
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%exitcond = icmp eq i32 %lftr.wideiv, %0
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br i1 %exitcond, label %for2.loopexit , label %for2
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for2.loopexit:
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br label %for1.inc10
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for1.inc10:
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%indvars.iv.next24 = add nuw nsw i64 %indvars.iv23, 1
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%lftr.wideiv25 = trunc i64 %indvars.iv23 to i32
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%exitcond26 = icmp eq i32 %lftr.wideiv25, %0
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br i1 %exitcond26, label %for1.loopexit, label %for1.header
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for1.loopexit:
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br label %exit
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exit:
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ret void
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}
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; CHECK-LABEL: @interchange_02
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; CHECK: for1.header:
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; CHECK-NEXT: %indvars.iv23 = phi i64 [ 0, %for1.ph ], [ %indvars.iv.next24, %for1.inc10 ]
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; CHECK-NEXT: br i1 %cmp219, label %for2.split1, label %for1.loopexit
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; CHECK: for2.split1:
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; CHECK: br label %for2.loopexit
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; CHECK: for2.split:
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; CHECK-NEXT: %indvars.iv.next = add nuw nsw i64 %indvars.iv, 1
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; CHECK: br i1 %exitcond, label %for1.loopexit, label %for2
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; CHECK: for2.loopexit:
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; CHECK-NEXT: br label %for1.inc10
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; CHECK: for1.inc10:
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; CHECK: br i1 %exitcond26, label %for2.split, label %for1.header
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@ -65,8 +65,8 @@ for.body9: ; preds = %for.body9, %for.con
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br i1 %exitcond, label %for.body9, label %for.cond.cleanup8
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}
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declare double @fn1()
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declare void @fn2(double)
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declare double @fn1() readnone
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declare void @fn2(double) readnone
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;; After interchange %indvars.iv (j) should increment as the middle loop.
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@ -93,7 +93,7 @@ for.end17:
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; CHECK: ret void
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declare void @foo(...)
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declare void @foo(...) readnone
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;; Loops not tightly nested are not interchanged
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;; for(int j=0;j<N;j++) {
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