From 6a567c5203e45b655d4021cdf1f41af87f6c458d Mon Sep 17 00:00:00 2001 From: Sanjay Patel Date: Thu, 4 Oct 2018 21:36:50 +0000 Subject: [InstCombine] drop poison flags in SimplifyVectorDemandedElts We established the (unfortunately complicated) rules for UB/poison propagation with vector ops in: D48893 D48987 D49047 It's clear from the affected tests that we are potentially creating poison where none existed before the transforms. For add/sub/mul, the answer is simple: just drop the flags because the extra undef vector lanes are generally more valuable for analysis and codegen. --- llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp | 7 +++++-- llvm/test/Transforms/InstCombine/X86/x86-muldq.ll | 2 +- llvm/test/Transforms/InstCombine/shuffle_select.ll | 2 +- llvm/test/Transforms/InstCombine/vec_demanded_elts.ll | 6 +++--- 4 files changed, 10 insertions(+), 7 deletions(-) diff --git a/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp b/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp index f8b57eeb388..936daa828a5 100644 --- a/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp +++ b/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp @@ -1592,8 +1592,11 @@ Value *InstCombiner::SimplifyDemandedVectorElts(Value *V, APInt DemandedElts, simplifyAndSetOp(I, 0, DemandedElts, UndefElts); simplifyAndSetOp(I, 1, DemandedElts, UndefElts2); - // TODO: If this is a potentially poison-producing instruction, we need - // to drop the wrapping/exact flags? + // Any change to an instruction with potential poison must clear those flags + // because we can not guarantee those constraints now. Other analysis may + // determine that it is safe to re-apply the flags. + if (MadeChange) + BO->dropPoisonGeneratingFlags(); // Output elements are undefined if both are undefined. Consider things // like undef & 0. The result is known zero, not undef. diff --git a/llvm/test/Transforms/InstCombine/X86/x86-muldq.ll b/llvm/test/Transforms/InstCombine/X86/x86-muldq.ll index ec4a31b6fd3..be1ba8ad14e 100644 --- a/llvm/test/Transforms/InstCombine/X86/x86-muldq.ll +++ b/llvm/test/Transforms/InstCombine/X86/x86-muldq.ll @@ -165,7 +165,7 @@ define <2 x i64> @test_demanded_elts_pmuludq_128(<4 x i32> %a0, <4 x i32> %a1) { ; CHECK-NEXT: [[TMP4:%.*]] = bitcast <4 x i32> [[TMP2]] to <2 x i64> ; CHECK-NEXT: [[TMP5:%.*]] = and <2 x i64> [[TMP3]], ; CHECK-NEXT: [[TMP6:%.*]] = and <2 x i64> [[TMP4]], -; CHECK-NEXT: [[TMP7:%.*]] = mul nuw <2 x i64> [[TMP5]], [[TMP6]] +; CHECK-NEXT: [[TMP7:%.*]] = mul <2 x i64> [[TMP5]], [[TMP6]] ; CHECK-NEXT: [[TMP8:%.*]] = shufflevector <2 x i64> [[TMP7]], <2 x i64> undef, <2 x i32> zeroinitializer ; CHECK-NEXT: ret <2 x i64> [[TMP8]] ; diff --git a/llvm/test/Transforms/InstCombine/shuffle_select.ll b/llvm/test/Transforms/InstCombine/shuffle_select.ll index 61a333a080c..c39237e3569 100644 --- a/llvm/test/Transforms/InstCombine/shuffle_select.ll +++ b/llvm/test/Transforms/InstCombine/shuffle_select.ll @@ -1413,7 +1413,7 @@ define <4 x i8> @or_add_not_enough_masking(<4 x i8> %v) { ; CHECK-LABEL: @or_add_not_enough_masking( ; CHECK-NEXT: [[V0:%.*]] = lshr <4 x i8> [[V:%.*]], ; CHECK-NEXT: [[T1:%.*]] = or <4 x i8> [[V0]], -; CHECK-NEXT: [[T2:%.*]] = add nuw nsw <4 x i8> [[V0]], +; CHECK-NEXT: [[T2:%.*]] = add <4 x i8> [[V0]], ; CHECK-NEXT: [[T3:%.*]] = shufflevector <4 x i8> [[T1]], <4 x i8> [[T2]], <4 x i32> ; CHECK-NEXT: ret <4 x i8> [[T3]] ; diff --git a/llvm/test/Transforms/InstCombine/vec_demanded_elts.ll b/llvm/test/Transforms/InstCombine/vec_demanded_elts.ll index 288b9e3ff21..838bc535888 100644 --- a/llvm/test/Transforms/InstCombine/vec_demanded_elts.ll +++ b/llvm/test/Transforms/InstCombine/vec_demanded_elts.ll @@ -202,7 +202,7 @@ define <4 x float> @inselt_shuf_no_demand_bogus_insert_index_in_chain(float %a1, define <3 x i8> @shuf_add(<3 x i8> %x) { ; CHECK-LABEL: @shuf_add( -; CHECK-NEXT: [[BO:%.*]] = add nsw <3 x i8> [[X:%.*]], +; CHECK-NEXT: [[BO:%.*]] = add <3 x i8> [[X:%.*]], ; CHECK-NEXT: [[R:%.*]] = shufflevector <3 x i8> [[BO]], <3 x i8> undef, <3 x i32> ; CHECK-NEXT: ret <3 x i8> [[R]] ; @@ -213,7 +213,7 @@ define <3 x i8> @shuf_add(<3 x i8> %x) { define <3 x i8> @shuf_sub(<3 x i8> %x) { ; CHECK-LABEL: @shuf_sub( -; CHECK-NEXT: [[BO:%.*]] = sub nuw <3 x i8> , [[X:%.*]] +; CHECK-NEXT: [[BO:%.*]] = sub <3 x i8> , [[X:%.*]] ; CHECK-NEXT: ret <3 x i8> [[BO]] ; %bo = sub nuw <3 x i8> , %x @@ -223,7 +223,7 @@ define <3 x i8> @shuf_sub(<3 x i8> %x) { define <3 x i8> @shuf_mul(<3 x i8> %x) { ; CHECK-LABEL: @shuf_mul( -; CHECK-NEXT: [[BO:%.*]] = mul nsw <3 x i8> [[X:%.*]], +; CHECK-NEXT: [[BO:%.*]] = mul <3 x i8> [[X:%.*]], ; CHECK-NEXT: [[R:%.*]] = shufflevector <3 x i8> [[BO]], <3 x i8> undef, <3 x i32> ; CHECK-NEXT: ret <3 x i8> [[R]] ; -- cgit v1.2.3