From 6fec6552f54885ae06bf76b35f9f1173a0561a4c Mon Sep 17 00:00:00 2001 From: Philip Reames Date: Mon, 13 Sep 2021 10:11:18 -0700 Subject: [PATCH] Revert "[IndVars] Replace PHIs if loop exits on 1st iteration" This reverts commit 5a6dfb27ca7424f15a20f9bb7ec90d858865faa3. See original review for why. --- llvm/lib/Transforms/Scalar/IndVarSimplify.cpp | 16 ++-------------- .../IndVarSimplify/eliminate-backedge.ll | 11 +++++++---- .../IndVarSimplify/eliminate-exit-no-dl.ll | 5 +++-- .../IndVarSimplify/floating-point-iv.ll | 4 +++- 4 files changed, 15 insertions(+), 21 deletions(-) diff --git a/llvm/lib/Transforms/Scalar/IndVarSimplify.cpp b/llvm/lib/Transforms/Scalar/IndVarSimplify.cpp index 320e20ca341c5..9b665bba4c97f 100644 --- a/llvm/lib/Transforms/Scalar/IndVarSimplify.cpp +++ b/llvm/lib/Transforms/Scalar/IndVarSimplify.cpp @@ -1309,17 +1309,6 @@ static void foldExit(const Loop *L, BasicBlock *ExitingBB, bool IsTaken, replaceExitCond(BI, NewCond, DeadInsts); } -static void replaceLoopPHINodesWithPreheaderValues( - Loop *L, SmallVectorImpl &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; } diff --git a/llvm/test/Transforms/IndVarSimplify/eliminate-backedge.ll b/llvm/test/Transforms/IndVarSimplify/eliminate-backedge.ll index e2ba6e084dce6..34bc4f6384278 100644 --- a/llvm/test/Transforms/IndVarSimplify/eliminate-backedge.ll +++ b/llvm/test/Transforms/IndVarSimplify/eliminate-backedge.ll @@ -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() diff --git a/llvm/test/Transforms/IndVarSimplify/eliminate-exit-no-dl.ll b/llvm/test/Transforms/IndVarSimplify/eliminate-exit-no-dl.ll index d8e0484b5207e..0abfb06bfe2b0 100644 --- a/llvm/test/Transforms/IndVarSimplify/eliminate-exit-no-dl.ll +++ b/llvm/test/Transforms/IndVarSimplify/eliminate-exit-no-dl.ll @@ -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]] diff --git a/llvm/test/Transforms/IndVarSimplify/floating-point-iv.ll b/llvm/test/Transforms/IndVarSimplify/floating-point-iv.ll index ca081e81b3ee1..f22e606d929f6 100644 --- a/llvm/test/Transforms/IndVarSimplify/floating-point-iv.ll +++ b/llvm/test/Transforms/IndVarSimplify/floating-point-iv.ll @@ -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