[llvm] r332695 - [LICM] Extend the MustExecute scope

[Serguei Katkov via llvm-commits]

Author: skatkov
Date: Thu May 17 21:56:28 2018
New Revision: 332695

URL: http://llvm.org/viewvc/llvm-project?rev=332695&view=rev
Log:
[LICM] Extend the MustExecute scope

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


Added:
    llvm/trunk/test/Analysis/MustExecute/const-cond.ll
Modified:
    llvm/trunk/lib/Analysis/MustExecute.cpp
    llvm/trunk/test/Transforms/LICM/hoist-mustexec.ll

Modified: llvm/trunk/lib/Analysis/MustExecute.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/MustExecute.cpp?rev=332695&r1=332694&r2=332695&view=diff
==============================================================================
--- llvm/trunk/lib/Analysis/MustExecute.cpp (original)
+++ llvm/trunk/lib/Analysis/MustExecute.cpp Thu May 17 21:56:28 2018
@@ -70,6 +70,10 @@ static bool CanProveNotTakenFirstIterati
   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;

Added: llvm/trunk/test/Analysis/MustExecute/const-cond.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Analysis/MustExecute/const-cond.ll?rev=332695&view=auto
==============================================================================
--- llvm/trunk/test/Analysis/MustExecute/const-cond.ll (added)
+++ llvm/trunk/test/Analysis/MustExecute/const-cond.ll Thu May 17 21:56:28 2018
@@ -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
+}
+

Modified: llvm/trunk/test/Transforms/LICM/hoist-mustexec.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/LICM/hoist-mustexec.ll?rev=332695&r1=332694&r2=332695&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/LICM/hoist-mustexec.ll (original)
+++ llvm/trunk/test/Transforms/LICM/hoist-mustexec.ll Thu May 17 21:56:28 2018
@@ -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: