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[LICM] Extend the MustExecute scope

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CanProveNotTakenFirstIteration utility does not handle the case when
condition of the branch is a constant. Add its handling.

Reviewers: reames, anna, mkazantsev
Reviewed By: reames
Subscribers: llvm-commits
Differential Revision: https://reviews.llvm.org/D46996

llvm-svn: 332695
This commit is contained in:
Serguei Katkov 2018-05-18 04:56:28 +00:00
parent 8c58acf7f0
commit bfdf0db09d
3 changed files with 58 additions and 3 deletions
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4
lib/Analysis/MustExecute.cpp
View File

@ -70,6 +70,10 @@ static bool CanProveNotTakenFirstIteration(BasicBlock *ExitBlock,
auto *BI = dyn_cast<BranchInst>(CondExitBlock->getTerminator());
if (!BI || !BI->isConditional())
return false;
// If condition is constant and false leads to ExitBlock then we always
// execute the true branch.
if (auto *Cond = dyn_cast<ConstantInt>(BI->getCondition()))
return BI->getSuccessor(Cond->getZExtValue() ? 1 : 0) == ExitBlock;
auto *Cond = dyn_cast<CmpInst>(BI->getCondition());
if (!Cond)
return false;

46
test/Analysis/MustExecute/const-cond.ll Normal file
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@ -0,0 +1,46 @@
; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
; RUN: opt -disable-output -print-mustexecute %s 2>&1 | FileCheck %s
; In general the CFG below is easily simplified but this is useful for
; pass ordering issue elimination.
define i1 @const_cond(i32 %high) {
; CHECK-LABEL: @const_cond(
; CHECK-NEXT: entry:
; CHECK-NEXT: br label [[LOOP:%.*]]
; CHECK: loop:
; CHECK-NEXT: [[IV:%.*]] = phi i32 [ 0, [[ENTRY:%.*]] ], [ [[IV_NEXT:%.*]], [[BACKEDGE:%.*]] ] ; (mustexec in: loop)
; CHECK-NEXT: br i1 true, label [[NEXT:%.*]], label [[NEVER1:%.*]] ; (mustexec in: loop)
; CHECK: next:
; CHECK-NEXT: br i1 false, label [[NEVER2:%.*]], label [[BACKEDGE]] ; (mustexec in: loop)
; CHECK: backedge:
; CHECK-NEXT: [[IV_NEXT]] = add nuw nsw i32 [[IV]], 1 ; (mustexec in: loop)
; CHECK-NEXT: [[EXIT_TEST:%.*]] = icmp slt i32 [[IV]], [[HIGH:%.*]] ; (mustexec in: loop)
; CHECK-NEXT: br i1 [[EXIT_TEST]], label [[LOOP]], label [[EXIT:%.*]] ; (mustexec in: loop)
; CHECK: exit:
; CHECK-NEXT: ret i1 false
; CHECK: never1:
; CHECK-NEXT: unreachable
; CHECK: never2:
; CHECK-NEXT: unreachable
;
entry:
br label %loop
loop:
%iv = phi i32 [0, %entry], [%iv.next, %backedge]
br i1 true, label %next, label %never1
next:
br i1 false, label %never2, label %backedge
backedge:
%iv.next = add nsw nuw i32 %iv, 1
%exit.test = icmp slt i32 %iv, %high
br i1 %exit.test, label %loop, label %exit
exit:
ret i1 false
never1:
unreachable
never2:
unreachable
}

11
test/Transforms/LICM/hoist-mustexec.ll
View File

@ -223,9 +223,14 @@ entry:
for.body:
%iv = phi i32 [ 0, %entry ], [ %inc, %continue ]
%acc = phi i32 [ 0, %entry ], [ %add, %continue ]
br label %dummy_block
dummy_block:
%wrongphi = phi i32 [12, %for.body]
%cond = icmp ult i32 %iv, 500
br i1 %cond, label %dummy_block1, label %dummy_block2
dummy_block1:
br label %dummy_block2
dummy_block2:
%wrongphi = phi i32 [11, %for.body], [12, %dummy_block1]
%r.chk = icmp ugt i32 %wrongphi, 2000
br i1 %r.chk, label %fail, label %continue
continue: