[PATCH] D108910: [IndVars] Break backedge and replace PHIs if loop exits on 1st iteration

[Max Kazantsev via Phabricator via llvm-commits]

This revision was automatically updated to reflect the committed changes.
Closed by commit rGd9ca444835e6: [IndVars] Break backedge and replace PHIs if loop exits on 1st iteration (authored by mkazantsev).

Changed prior to commit:
  https://reviews.llvm.org/D108910?vs=370847&id=372156#toc

Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D108910/new/

https://reviews.llvm.org/D108910

Files:
  llvm/lib/Transforms/Scalar/IndVarSimplify.cpp
  llvm/test/Transforms/IndVarSimplify/eliminate-backedge.ll


Index: llvm/test/Transforms/IndVarSimplify/eliminate-backedge.ll
===================================================================
--- llvm/test/Transforms/IndVarSimplify/eliminate-backedge.ll
+++ llvm/test/Transforms/IndVarSimplify/eliminate-backedge.ll
@@ -15,7 +15,6 @@
 ; CHECK:       loop_preheader:
 ; CHECK-NEXT:    br label %loop
 ; CHECK:       loop:
-; CHECK-NEXT:    %iv.next = add nuw nsw i32 0, 1
 ; CHECK-NEXT:    %left_ptr = getelementptr inbounds i8, i8* %lhs, i32 0
 ; CHECK-NEXT:    %right_ptr = getelementptr inbounds i8, i8* %rhs, i32 0
 ; CHECK-NEXT:    %result = call i1 @foo(i8* %left_ptr, i8* %right_ptr)
@@ -25,12 +24,10 @@
 ; CHECK-NEXT:    br i1 false, label %exiting_2, label %exit.loopexit
 ; CHECK:       exiting_2:
 ; CHECK-NEXT:    %bar_ret = call i1 @bar()
-; CHECK-NEXT:    br i1 %bar_ret, label %exit.loopexit, label %exiting_3
+; CHECK-NEXT:    br i1 true, label %exit.loopexit, label %exiting_3
 ; CHECK:       exiting_3:
 ; CHECK-NEXT:    %baz_ret = call i1 @baz()
-; CHECK-NEXT:    %continue = icmp ne i32 %iv.next, %len
-; CHECK-NEXT:    %or.cond = select i1 %baz_ret, i1 %continue, i1 false
-; CHECK-NEXT:    br i1 %or.cond, label %loop, label %exit.loopexit
+; CHECK-NEXT:    br i1 false, label %loop, label %exit.loopexit
 ; CHECK:       exit.loopexit:
 ; CHECK-NEXT:    %val.ph = phi i1 [ %baz_ret, %exiting_3 ], [ %bar_ret, %exiting_2 ], [ %iv.wide.is_not_zero, %exiting_1 ], [ %result, %loop ]
 ; CHECK-NEXT:    br label %exit
Index: llvm/lib/Transforms/Scalar/IndVarSimplify.cpp
===================================================================
--- llvm/lib/Transforms/Scalar/IndVarSimplify.cpp
+++ llvm/lib/Transforms/Scalar/IndVarSimplify.cpp
@@ -1465,8 +1465,15 @@
 
   bool Changed = false;
   bool SkipLastIter = false;
+  bool ExitsOnFirstIter = false;
   SmallSet<const SCEV*, 8> DominatingExitCounts;
   for (BasicBlock *ExitingBB : ExitingBlocks) {
+    if (ExitsOnFirstIter) {
+      // If proved that some earlier exit is taken
+      // on 1st iteration, then fold this one.
+      foldExit(L, ExitingBB, true, DeadInsts);
+      continue;
+    }
     const SCEV *ExitCount = SE->getExitCount(L, ExitingBB);
     if (isa<SCEVCouldNotCompute>(ExitCount)) {
       // Okay, we do not know the exit count here. Can we at least prove that it
@@ -1516,6 +1523,7 @@
       foldExit(L, ExitingBB, true, DeadInsts);
       replaceLoopPHINodesWithPreheaderValues(L, DeadInsts);
       Changed = true;
+      ExitsOnFirstIter = true;
       continue;
     }
 


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