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Revert "[IndVars] Replace PHIs if loop exits on 1st iteration" 

This reverts commit 5a6dfb27ca.  See original review for why.
This commit is contained in:
Philip Reames 2021-09-13 10:11:18 -07:00
parent 5746c76f3f
commit 6fec6552f5
4 changed files with 15 additions and 21 deletions
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16
llvm/lib/Transforms/Scalar/IndVarSimplify.cpp
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@ -1309,17 +1309,6 @@ static void foldExit(const Loop *L, BasicBlock *ExitingBB, bool IsTaken,
replaceExitCond(BI, NewCond, DeadInsts);
}
static void replaceLoopPHINodesWithPreheaderValues(
Loop *L, SmallVectorImpl<WeakTrackingVH> &DeadInsts) {
auto *LoopPreheader = L->getLoopPreheader();
auto *LoopHeader = L->getHeader();
for (auto &PN : LoopHeader->phis()) {
auto *PreheaderIncoming = PN.getIncomingValueForBlock(LoopPreheader);
PN.replaceAllUsesWith(PreheaderIncoming);
DeadInsts.emplace_back(&PN);
}
}
static void replaceWithInvariantCond(
const Loop *L, BasicBlock *ExitingBB, ICmpInst::Predicate InvariantPred,
const SCEV *InvariantLHS, const SCEV *InvariantRHS, SCEVExpander &Rewriter,
@ -1510,11 +1499,10 @@ bool IndVarSimplify::optimizeLoopExits(Loop *L, SCEVExpander &Rewriter) {
// If we know we'd exit on the first iteration, rewrite the exit to
// reflect this. This does not imply the loop must exit through this
// exit; there may be an earlier one taken on the first iteration.
// We know that the backedge can't be taken, so we replace all
// the header PHIs with values coming from the preheader.
// TODO: Given we know the backedge can't be taken, we should go ahead
// and break it. Or at least, kill all the header phis and simplify.
if (ExitCount->isZero()) {
foldExit(L, ExitingBB, true, DeadInsts);
replaceLoopPHINodesWithPreheaderValues(L, DeadInsts);
Changed = true;
continue;
}

11
llvm/test/Transforms/IndVarSimplify/eliminate-backedge.ll
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@ -15,13 +15,16 @@ define i1 @kill_backedge_and_phis(i8* align 1 %lhs, i8* align 1 %rhs, i32 %len)
; 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: %iv = phi i32 [ 0, %loop_preheader ], [ %iv.next, %exiting_3 ]
; CHECK-NEXT: %iv.wide = phi i64 [ 0, %loop_preheader ], [ %iv.wide.next, %exiting_3 ]
; CHECK-NEXT: %iv.next = add nuw nsw i32 %iv, 1
; CHECK-NEXT: %iv.wide.next = add nuw nsw i64 %iv.wide, 1
; CHECK-NEXT: %left_ptr = getelementptr inbounds i8, i8* %lhs, i32 %iv
; CHECK-NEXT: %right_ptr = getelementptr inbounds i8, i8* %rhs, i32 %iv
; CHECK-NEXT: %result = call i1 @foo(i8* %left_ptr, i8* %right_ptr)
; CHECK-NEXT: br i1 %result, label %exiting_1, label %exit.loopexit
; CHECK: exiting_1:
; CHECK-NEXT: %iv.wide.is_not_zero = icmp ne i64 0, 0
; CHECK-NEXT: %iv.wide.is_not_zero = icmp ne i64 %iv.wide, 0
; CHECK-NEXT: br i1 false, label %exiting_2, label %exit.loopexit
; CHECK: exiting_2:
; CHECK-NEXT: %bar_ret = call i1 @bar()

5
llvm/test/Transforms/IndVarSimplify/eliminate-exit-no-dl.ll
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@ -14,9 +14,10 @@ define void @foo() {
; CHECK-NEXT: bb:
; CHECK-NEXT: br label [[BB3:%.*]]
; CHECK: bb3:
; CHECK-NEXT: [[TMP4:%.*]] = getelementptr inbounds i8, i8* getelementptr inbounds ([0 x i8], [0 x i8]* @global, i64 0, i64 2), i64 -1
; CHECK-NEXT: [[TMP:%.*]] = phi i8* [ [[TMP4:%.*]], [[BB7:%.*]] ], [ getelementptr inbounds ([0 x i8], [0 x i8]* @global, i64 0, i64 2), [[BB:%.*]] ]
; CHECK-NEXT: [[TMP4]] = getelementptr inbounds i8, i8* [[TMP]], i64 -1
; CHECK-NEXT: [[TMP6:%.*]] = load i8, i8* [[TMP4]], align 1
; CHECK-NEXT: br i1 false, label [[BB7:%.*]], label [[BB11:%.*]]
; CHECK-NEXT: br i1 false, label [[BB7]], label [[BB11:%.*]]
; CHECK: bb7:
; CHECK-NEXT: [[TMP8:%.*]] = zext i8 [[TMP6]] to i64
; CHECK-NEXT: br i1 true, label [[BB11]], label [[BB3]]

4
llvm/test/Transforms/IndVarSimplify/floating-point-iv.ll
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@ -65,7 +65,9 @@ define void @test3() nounwind {
; CHECK-NEXT: entry:
; CHECK-NEXT: br label [[BB:%.*]]
; CHECK: bb:
; CHECK-NEXT: [[TMP0:%.*]] = tail call i32 @foo(double 0.000000e+00) #[[ATTR0]]
; CHECK-NEXT: [[IV:%.*]] = phi double [ 0.000000e+00, [[ENTRY:%.*]] ], [ [[TMP1:%.*]], [[BB]] ]
; CHECK-NEXT: [[TMP0:%.*]] = tail call i32 @foo(double [[IV]]) #[[ATTR0]]
; CHECK-NEXT: [[TMP1]] = fadd double [[IV]], 1.000000e+00
; CHECK-NEXT: br i1 false, label [[BB]], label [[RETURN:%.*]]
; CHECK: return:
; CHECK-NEXT: ret void