From 4c0da2366305c49672d89ee0e90afcf85fa2641f Mon Sep 17 00:00:00 2001 From: Max Kazantsev Date: Sat, 9 Oct 2021 14:47:44 +0700 Subject: [PATCH] [LoopDeletion] Support selects when symbolically evaluating 1st iteration Adds support for selects for which we know value on the 1st iteration. Differential Revision: https://reviews.llvm.org/D104111 Reviewed By: nikic --- llvm/lib/Transforms/Scalar/LoopDeletion.cpp | 8 ++++++++ .../test/Transforms/LoopDeletion/eval_first_iteration.ll | 9 ++++----- 2 files changed, 12 insertions(+), 5 deletions(-) diff --git a/llvm/lib/Transforms/Scalar/LoopDeletion.cpp b/llvm/lib/Transforms/Scalar/LoopDeletion.cpp index e1e5ef958363..03f7f259aa2f 100644 --- a/llvm/lib/Transforms/Scalar/LoopDeletion.cpp +++ b/llvm/lib/Transforms/Scalar/LoopDeletion.cpp @@ -197,6 +197,14 @@ getValueOnFirstIteration(Value *V, DenseMap &FirstIterValue, Value *RHS = getValueOnFirstIteration(Cmp->getOperand(1), FirstIterValue, SQ); FirstIterV = SimplifyICmpInst(Cmp->getPredicate(), LHS, RHS, SQ); + } else if (auto *Select = dyn_cast(V)) { + Value *Cond = + getValueOnFirstIteration(Select->getCondition(), FirstIterValue, SQ); + if (auto *C = dyn_cast(Cond)) { + auto *Selected = C->isAllOnesValue() ? Select->getTrueValue() + : Select->getFalseValue(); + FirstIterV = getValueOnFirstIteration(Selected, FirstIterValue, SQ); + } } if (!FirstIterV) FirstIterV = V; diff --git a/llvm/test/Transforms/LoopDeletion/eval_first_iteration.ll b/llvm/test/Transforms/LoopDeletion/eval_first_iteration.ll index 18f4805191c7..1bdcefc419ce 100644 --- a/llvm/test/Transforms/LoopDeletion/eval_first_iteration.ll +++ b/llvm/test/Transforms/LoopDeletion/eval_first_iteration.ll @@ -979,25 +979,24 @@ failure: unreachable } -; TODO: We can break the backedge here. define i32 @test_select_const(i32 %x) { ; CHECK-LABEL: @test_select_const( ; CHECK-NEXT: entry: ; CHECK-NEXT: br label [[LOOP:%.*]] ; CHECK: loop: -; CHECK-NEXT: [[SUM:%.*]] = phi i32 [ 0, [[ENTRY:%.*]] ], [ [[SUM_NEXT:%.*]], [[BACKEDGE:%.*]] ] +; CHECK-NEXT: [[SUM:%.*]] = phi i32 [ 0, [[ENTRY:%.*]] ] ; CHECK-NEXT: [[SUB:%.*]] = sub i32 4, [[SUM]] ; CHECK-NEXT: [[IS_POSITIVE:%.*]] = icmp sgt i32 [[SUB]], 0 ; CHECK-NEXT: [[SEL:%.*]] = select i1 [[IS_POSITIVE]], i32 [[SUB]], i32 [[X:%.*]] ; CHECK-NEXT: [[SEL_COND:%.*]] = icmp sgt i32 [[SEL]], 0 -; CHECK-NEXT: br i1 [[SEL_COND]], label [[BACKEDGE]], label [[IF_FALSE:%.*]] +; CHECK-NEXT: br i1 [[SEL_COND]], label [[BACKEDGE:%.*]], label [[IF_FALSE:%.*]] ; CHECK: if.false: ; CHECK-NEXT: br label [[BACKEDGE]] ; CHECK: backedge: ; CHECK-NEXT: [[MERGE_PHI:%.*]] = phi i32 [ 0, [[IF_FALSE]] ], [ [[SUB]], [[LOOP]] ] -; CHECK-NEXT: [[SUM_NEXT]] = add i32 [[SUM]], [[MERGE_PHI]] +; CHECK-NEXT: [[SUM_NEXT:%.*]] = add i32 [[SUM]], [[MERGE_PHI]] ; CHECK-NEXT: [[LOOP_COND:%.*]] = icmp ne i32 [[SUM_NEXT]], 4 -; CHECK-NEXT: br i1 [[LOOP_COND]], label [[LOOP]], label [[DONE:%.*]] +; CHECK-NEXT: br label [[DONE:%.*]] ; CHECK: done: ; CHECK-NEXT: [[SUM_NEXT_LCSSA:%.*]] = phi i32 [ [[SUM_NEXT]], [[BACKEDGE]] ] ; CHECK-NEXT: ret i32 [[SUM_NEXT_LCSSA]]