From b81558a8e11d49fc2af954bae2c122ccfeee39eb Mon Sep 17 00:00:00 2001 From: Chad Rosier Date: Thu, 23 Feb 2017 18:49:03 +0000 Subject: [PATCH] [Reassociate] Add negated value of negative constant to the Duplicates list. In OptimizeAdd, we scan the operand list to see if there are any common factors between operands that can be factored out to reduce the number of multiplies (e.g., 'A*A+A*B*C+D' -> 'A*(A+B*C)+D'). For each operand of the operand list, we only consider unique factors (which is tracked by the Duplicate set). Now if we find a factor that is a negative constant, we add the negated value as a factor as well, because we can percolate the negate out. However, we mistakenly don't add this negated constant to the Duplicates set. Consider the expression A*2*-2 + B. Obviously, nothing to factor. For the added value A*2*-2 we over count 2 as a factor without this change, which causes the assert reported in PR30256. The problem is that this code is assuming that all the multiply operands of the add are already reassociated. This change avoids the issue by making OptimizeAdd tolerate multiplies which haven't been completely optimized; this sort of works, but we're doing wasted work: we'll end up revisiting the add later anyway. Another possible approach would be to enforce RPO iteration order more strongly. If we have RedoInsts, we process them immediately in RPO order, rather than waiting until we've finished processing the whole function. Intuitively, it seems like the natural approach: reassociation works on expression trees, so the optimization only works in one direction. That said, I'm not sure how practical that is given the current Reassociate; the "optimal" form for an expression depends on its use list (see all the uses of "user_back()"), so Reassociate is really an iterative optimization of sorts, so any changes here would probably get messy. PR30256 Differential Revision: https://reviews.llvm.org/D30228 git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@296003 91177308-0d34-0410-b5e6-96231b3b80d8 --- lib/Transforms/Scalar/Reassociate.cpp | 8 ++++---- test/Transforms/Reassociate/basictest.ll | 20 ++++++++++++++++++++ 2 files changed, 24 insertions(+), 4 deletions(-) diff --git a/lib/Transforms/Scalar/Reassociate.cpp b/lib/Transforms/Scalar/Reassociate.cpp index dc03c5c33d1..3dcab609078 100644 --- a/lib/Transforms/Scalar/Reassociate.cpp +++ b/lib/Transforms/Scalar/Reassociate.cpp @@ -1520,8 +1520,8 @@ Value *ReassociatePass::OptimizeAdd(Instruction *I, if (ConstantInt *CI = dyn_cast(Factor)) { if (CI->isNegative() && !CI->isMinValue(true)) { Factor = ConstantInt::get(CI->getContext(), -CI->getValue()); - assert(!Duplicates.count(Factor) && - "Shouldn't have two constant factors, missed a canonicalize"); + if (!Duplicates.insert(Factor).second) + continue; unsigned Occ = ++FactorOccurrences[Factor]; if (Occ > MaxOcc) { MaxOcc = Occ; @@ -1533,8 +1533,8 @@ Value *ReassociatePass::OptimizeAdd(Instruction *I, APFloat F(CF->getValueAPF()); F.changeSign(); Factor = ConstantFP::get(CF->getContext(), F); - assert(!Duplicates.count(Factor) && - "Shouldn't have two constant factors, missed a canonicalize"); + if (!Duplicates.insert(Factor).second) + continue; unsigned Occ = ++FactorOccurrences[Factor]; if (Occ > MaxOcc) { MaxOcc = Occ; diff --git a/test/Transforms/Reassociate/basictest.ll b/test/Transforms/Reassociate/basictest.ll index 11c67bea2cb..4703fd7621b 100644 --- a/test/Transforms/Reassociate/basictest.ll +++ b/test/Transforms/Reassociate/basictest.ll @@ -222,3 +222,23 @@ define i32 @test15(i32 %X1, i32 %X2, i32 %X3) { ; CHECK-LABEL: @test15 ; CHECK: and i1 %A, %B } + +; PR30256 - previously this asserted. +; CHECK-LABEL: @test16 +; CHECK: %[[FACTOR:.*]] = mul i64 %a, -4 +; CHECK-NEXT: %[[RES:.*]] = add i64 %[[FACTOR]], %b +; CHECK-NEXT: ret i64 %[[RES]] +define i64 @test16(i1 %cmp, i64 %a, i64 %b) { +entry: + %shl = shl i64 %a, 1 + %shl.neg = sub i64 0, %shl + br i1 %cmp, label %if.then, label %if.end + +if.then: ; preds = %entry + %add1 = add i64 %shl.neg, %shl.neg + %add2 = add i64 %add1, %b + ret i64 %add2 + +if.end: ; preds = %entry + ret i64 0 +} -- 2.50.1