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Revert "[IndVars] Break backedge and replace PHIs if loop exits on 1st iteration" 

This reverts commit d9ca444835.  See review for why.
This commit is contained in:
Philip Reames 2021-09-13 10:10:49 -07:00
parent 1a56a291c5
commit 5746c76f3f
2 changed files with 5 additions and 10 deletions
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8
llvm/lib/Transforms/Scalar/IndVarSimplify.cpp
View File

@ -1465,15 +1465,8 @@ bool IndVarSimplify::optimizeLoopExits(Loop *L, SCEVExpander &Rewriter) {
bool Changed = false; bool Changed = false;
bool SkipLastIter = false; bool SkipLastIter = false;
bool ExitsOnFirstIter = false;
SmallSet<const SCEV*, 8> DominatingExitCounts; SmallSet<const SCEV*, 8> DominatingExitCounts;
for (BasicBlock *ExitingBB : ExitingBlocks) { 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); const SCEV *ExitCount = SE->getExitCount(L, ExitingBB);
if (isa<SCEVCouldNotCompute>(ExitCount)) { if (isa<SCEVCouldNotCompute>(ExitCount)) {
// Okay, we do not know the exit count here. Can we at least prove that it // Okay, we do not know the exit count here. Can we at least prove that it
@ -1523,7 +1516,6 @@ bool IndVarSimplify::optimizeLoopExits(Loop *L, SCEVExpander &Rewriter) {
foldExit(L, ExitingBB, true, DeadInsts); foldExit(L, ExitingBB, true, DeadInsts);
replaceLoopPHINodesWithPreheaderValues(L, DeadInsts); replaceLoopPHINodesWithPreheaderValues(L, DeadInsts);
Changed = true; Changed = true;
ExitsOnFirstIter = true;
continue; continue;
} }

7
llvm/test/Transforms/IndVarSimplify/eliminate-backedge.ll
View File

@ -15,6 +15,7 @@ define i1 @kill_backedge_and_phis(i8* align 1 %lhs, i8* align 1 %rhs, i32 %len)
; CHECK: loop_preheader: ; CHECK: loop_preheader:
; CHECK-NEXT: br label %loop ; CHECK-NEXT: br label %loop
; CHECK: 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: %left_ptr = getelementptr inbounds i8, i8* %lhs, i32 0
; CHECK-NEXT: %right_ptr = getelementptr inbounds i8, i8* %rhs, 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) ; CHECK-NEXT: %result = call i1 @foo(i8* %left_ptr, i8* %right_ptr)
@ -24,10 +25,12 @@ define i1 @kill_backedge_and_phis(i8* align 1 %lhs, i8* align 1 %rhs, i32 %len)
; CHECK-NEXT: br i1 false, label %exiting_2, label %exit.loopexit ; CHECK-NEXT: br i1 false, label %exiting_2, label %exit.loopexit
; CHECK: exiting_2: ; CHECK: exiting_2:
; CHECK-NEXT: %bar_ret = call i1 @bar() ; CHECK-NEXT: %bar_ret = call i1 @bar()
; CHECK-NEXT: br i1 true, label %exit.loopexit, label %exiting_3 ; CHECK-NEXT: br i1 %bar_ret, label %exit.loopexit, label %exiting_3
; CHECK: exiting_3: ; CHECK: exiting_3:
; CHECK-NEXT: %baz_ret = call i1 @baz() ; CHECK-NEXT: %baz_ret = call i1 @baz()
; CHECK-NEXT: br i1 false, label %loop, label %exit.loopexit ; 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: 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: %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 ; CHECK-NEXT: br label %exit