From 59441c73296e7c489ac1d71ffda2de3060bdd4f8 Mon Sep 17 00:00:00 2001 From: Sanjay Patel Date: Mon, 11 Oct 2021 15:21:51 -0400 Subject: [PATCH] [InstCombine] fold signbit check of X | (X -1) There may be some other patterns like this or a generalization, but this is an example that I noticed would definitely regress with a planned follow-up to D111410. https://alive2.llvm.org/ce/z/GVpQDb --- .../InstCombine/InstCombineCompares.cpp | 11 ++++++++ llvm/test/Transforms/InstCombine/icmp-or.ll | 26 ++++++++++--------- llvm/test/Transforms/InstCombine/or.ll | 6 ++--- 3 files changed, 27 insertions(+), 16 deletions(-) diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp index d47e6160acbe..2f25be4fce08 100644 --- a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp +++ b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp @@ -1950,6 +1950,17 @@ Instruction *InstCombinerImpl::foldICmpOrConstant(ICmpInst &Cmp, } } + // (X | (X-1)) s< 0 --> X < 1 + // (X | (X-1)) s> -1 --> X > 0 + Value *X; + bool TrueIfSigned; + if (isSignBitCheck(Pred, C, TrueIfSigned) && + match(Or, m_c_Or(m_Add(m_Value(X), m_AllOnes()), m_Deferred(X)))) { + auto NewPred = TrueIfSigned ? ICmpInst::ICMP_SLT : ICmpInst::ICMP_SGT; + Constant *NewC = ConstantInt::get(X->getType(), TrueIfSigned ? 1 : 0); + return new ICmpInst(NewPred, X, NewC); + } + if (!Cmp.isEquality() || !C.isZero() || !Or->hasOneUse()) return nullptr; diff --git a/llvm/test/Transforms/InstCombine/icmp-or.ll b/llvm/test/Transforms/InstCombine/icmp-or.ll index 4df08814aaa5..de3f998814b7 100644 --- a/llvm/test/Transforms/InstCombine/icmp-or.ll +++ b/llvm/test/Transforms/InstCombine/icmp-or.ll @@ -220,9 +220,7 @@ define i1 @eq_const_mask_use2(i8 %x, i8 %y) { define <2 x i1> @decrement_slt_0(<2 x i8> %x) { ; CHECK-LABEL: @decrement_slt_0( -; CHECK-NEXT: [[DEC:%.*]] = add <2 x i8> [[X:%.*]], -; CHECK-NEXT: [[OR:%.*]] = or <2 x i8> [[DEC]], [[X]] -; CHECK-NEXT: [[R:%.*]] = icmp slt <2 x i8> [[OR]], zeroinitializer +; CHECK-NEXT: [[R:%.*]] = icmp slt <2 x i8> [[X:%.*]], ; CHECK-NEXT: ret <2 x i1> [[R]] ; %dec = add <2 x i8> %x, @@ -236,8 +234,7 @@ define i1 @decrement_slt_0_commute_use1(i8 %px) { ; CHECK-NEXT: [[X:%.*]] = mul i8 [[PX:%.*]], 42 ; CHECK-NEXT: [[DEC:%.*]] = add i8 [[X]], -1 ; CHECK-NEXT: call void @use(i8 [[DEC]]) -; CHECK-NEXT: [[OR:%.*]] = or i8 [[X]], [[DEC]] -; CHECK-NEXT: [[R:%.*]] = icmp slt i8 [[OR]], 0 +; CHECK-NEXT: [[R:%.*]] = icmp slt i8 [[X]], 1 ; CHECK-NEXT: ret i1 [[R]] ; %x = mul i8 %px, 42 ; thwart complexity-based canonicalization @@ -253,7 +250,7 @@ define i1 @decrement_slt_0_use2(i8 %x) { ; CHECK-NEXT: [[DEC:%.*]] = add i8 [[X:%.*]], -1 ; CHECK-NEXT: [[OR:%.*]] = or i8 [[DEC]], [[X]] ; CHECK-NEXT: call void @use(i8 [[OR]]) -; CHECK-NEXT: [[R:%.*]] = icmp slt i8 [[OR]], 0 +; CHECK-NEXT: [[R:%.*]] = icmp slt i8 [[X]], 1 ; CHECK-NEXT: ret i1 [[R]] ; %dec = add i8 %x, -1 @@ -263,6 +260,8 @@ define i1 @decrement_slt_0_use2(i8 %x) { ret i1 %r } +; negative test - wrong cmp constant + define i1 @decrement_slt_n1(i8 %x) { ; CHECK-LABEL: @decrement_slt_n1( ; CHECK-NEXT: [[DEC:%.*]] = add i8 [[X:%.*]], -1 @@ -276,6 +275,8 @@ define i1 @decrement_slt_n1(i8 %x) { ret i1 %r } +; negative test - wrong add constant + define i1 @not_decrement_slt_0(i8 %x) { ; CHECK-LABEL: @not_decrement_slt_0( ; CHECK-NEXT: [[DEC:%.*]] = add i8 [[X:%.*]], -2 @@ -293,9 +294,7 @@ define i1 @not_decrement_slt_0(i8 %x) { define <2 x i1> @decrement_sgt_n1(<2 x i8> %x) { ; CHECK-LABEL: @decrement_sgt_n1( -; CHECK-NEXT: [[DEC:%.*]] = add <2 x i8> [[X:%.*]], -; CHECK-NEXT: [[OR:%.*]] = or <2 x i8> [[DEC]], [[X]] -; CHECK-NEXT: [[R:%.*]] = icmp sgt <2 x i8> [[OR]], +; CHECK-NEXT: [[R:%.*]] = icmp sgt <2 x i8> [[X:%.*]], zeroinitializer ; CHECK-NEXT: ret <2 x i1> [[R]] ; %dec = add <2 x i8> %x, @@ -309,8 +308,7 @@ define i1 @decrement_sgt_n1_commute_use1(i8 %px) { ; CHECK-NEXT: [[X:%.*]] = mul i8 [[PX:%.*]], 42 ; CHECK-NEXT: [[DEC:%.*]] = add i8 [[X]], -1 ; CHECK-NEXT: call void @use(i8 [[DEC]]) -; CHECK-NEXT: [[OR:%.*]] = or i8 [[X]], [[DEC]] -; CHECK-NEXT: [[R:%.*]] = icmp sgt i8 [[OR]], -1 +; CHECK-NEXT: [[R:%.*]] = icmp sgt i8 [[X]], 0 ; CHECK-NEXT: ret i1 [[R]] ; %x = mul i8 %px, 42 ; thwart complexity-based canonicalization @@ -326,7 +324,7 @@ define i1 @decrement_sgt_n1_use2(i8 %x) { ; CHECK-NEXT: [[DEC:%.*]] = add i8 [[X:%.*]], -1 ; CHECK-NEXT: [[OR:%.*]] = or i8 [[DEC]], [[X]] ; CHECK-NEXT: call void @use(i8 [[OR]]) -; CHECK-NEXT: [[R:%.*]] = icmp sgt i8 [[OR]], -1 +; CHECK-NEXT: [[R:%.*]] = icmp sgt i8 [[X]], 0 ; CHECK-NEXT: ret i1 [[R]] ; %dec = add i8 %x, -1 @@ -336,6 +334,8 @@ define i1 @decrement_sgt_n1_use2(i8 %x) { ret i1 %r } +; negative test - wrong cmp constant + define i1 @decrement_sgt_0(i8 %x) { ; CHECK-LABEL: @decrement_sgt_0( ; CHECK-NEXT: [[DEC:%.*]] = add i8 [[X:%.*]], -1 @@ -349,6 +349,8 @@ define i1 @decrement_sgt_0(i8 %x) { ret i1 %r } +; negative test - wrong add constant + define i1 @not_decrement_sgt_n1(i8 %x) { ; CHECK-LABEL: @not_decrement_sgt_n1( ; CHECK-NEXT: [[DEC:%.*]] = add i8 [[X:%.*]], -2 diff --git a/llvm/test/Transforms/InstCombine/or.ll b/llvm/test/Transforms/InstCombine/or.ll index 5b4bff6f0c29..c50f226438ec 100644 --- a/llvm/test/Transforms/InstCombine/or.ll +++ b/llvm/test/Transforms/InstCombine/or.ll @@ -1447,10 +1447,8 @@ define i8 @lshr_bitwidth_mask(i8 %x, i8 %y) { define i1 @cmp_overlap(i32 %x) { ; CHECK-LABEL: @cmp_overlap( -; CHECK-NEXT: [[NOTSUB:%.*]] = add i32 [[X:%.*]], -1 -; CHECK-NEXT: [[TMP1:%.*]] = or i32 [[NOTSUB]], [[X]] -; CHECK-NEXT: [[TMP2:%.*]] = icmp slt i32 [[TMP1]], 0 -; CHECK-NEXT: ret i1 [[TMP2]] +; CHECK-NEXT: [[TMP1:%.*]] = icmp slt i32 [[X:%.*]], 1 +; CHECK-NEXT: ret i1 [[TMP1]] ; %isneg = icmp slt i32 %x, 0 %negx = sub i32 0, %x