[InstCombine] don't automatically drop poison-generating flags in SimplifyVectorDeman...

I noticed this while reviewing the test diffs in D115460
(and so the diffs in that patch will be reduced if this one is applied first).

This is effectively a revert of 3436dc29239d ( https://reviews.llvm.org/rG3436dc29239d ) -
since that commit, we've made several enhancements, so the reasoning there is no longer
valid. Specifically, we added a poison value to IR, and we clarified the behavior of
undef/poison elements in a shuffle mask:
https://llvm.org/docs/LangRef.html#shufflevector-instruction

Alive2 seems to agree that the propagation of flags in the test diffs shown here are valid:
https://alive2.llvm.org/ce/z/UuY-jr
https://alive2.llvm.org/ce/z/GXoMD9
https://alive2.llvm.org/ce/z/nVCyVH

Differential Revision: https://reviews.llvm.org/D115526

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp b/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
index e357a9d..4dc712f 100644 (file)
--- a/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
@@ -1595,12 +1595,6 @@ Value *InstCombinerImpl::SimplifyDemandedVectorElts(Value *V,
     simplifyAndSetOp(I, 0, DemandedElts, UndefElts);
     simplifyAndSetOp(I, 1, DemandedElts, UndefElts2);
 
-    // 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.
     UndefElts &= UndefElts2;

diff --git a/llvm/test/Transforms/InstCombine/X86/x86-muldq-inseltpoison.ll b/llvm/test/Transforms/InstCombine/X86/x86-muldq-inseltpoison.ll
index d7a2c82..68c77ef 100644 (file)
--- a/llvm/test/Transforms/InstCombine/X86/x86-muldq-inseltpoison.ll
+++ b/llvm/test/Transforms/InstCombine/X86/x86-muldq-inseltpoison.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]], <i64 4294967295, i64 poison>
 ; CHECK-NEXT:    [[TMP6:%.*]] = and <2 x i64> [[TMP4]], <i64 4294967295, i64 poison>
-; CHECK-NEXT:    [[TMP7:%.*]] = mul <2 x i64> [[TMP5]], [[TMP6]]
+; CHECK-NEXT:    [[TMP7:%.*]] = mul nuw <2 x i64> [[TMP5]], [[TMP6]]
 ; CHECK-NEXT:    [[TMP8:%.*]] = shufflevector <2 x i64> [[TMP7]], <2 x i64> poison, <2 x i32> zeroinitializer
 ; CHECK-NEXT:    ret <2 x i64> [[TMP8]]
 ;

diff --git a/llvm/test/Transforms/InstCombine/X86/x86-muldq.ll b/llvm/test/Transforms/InstCombine/X86/x86-muldq.ll
index c6e5f47..a26737e 100644 (file)
--- 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]], <i64 4294967295, i64 poison>
 ; CHECK-NEXT:    [[TMP6:%.*]] = and <2 x i64> [[TMP4]], <i64 4294967295, i64 poison>
-; CHECK-NEXT:    [[TMP7:%.*]] = mul <2 x i64> [[TMP5]], [[TMP6]]
+; CHECK-NEXT:    [[TMP7:%.*]] = mul nuw <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-inseltpoison.ll b/llvm/test/Transforms/InstCombine/shuffle_select-inseltpoison.ll
index bca56a8..53f2dd1 100644 (file)
--- a/llvm/test/Transforms/InstCombine/shuffle_select-inseltpoison.ll
+++ b/llvm/test/Transforms/InstCombine/shuffle_select-inseltpoison.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:%.*]], <i8 1, i8 1, i8 1, i8 1>
 ; CHECK-NEXT:    [[T1:%.*]] = or <4 x i8> [[V0]], <i8 poison, i8 poison, i8 -64, i8 -64>
-; CHECK-NEXT:    [[T2:%.*]] = add <4 x i8> [[V0]], <i8 1, i8 2, i8 poison, i8 poison>
+; CHECK-NEXT:    [[T2:%.*]] = add nuw nsw <4 x i8> [[V0]], <i8 1, i8 2, i8 poison, i8 poison>
 ; CHECK-NEXT:    [[T3:%.*]] = shufflevector <4 x i8> [[T2]], <4 x i8> [[T1]], <4 x i32> <i32 0, i32 1, i32 6, i32 7>
 ; CHECK-NEXT:    ret <4 x i8> [[T3]]
 ;

diff --git a/llvm/test/Transforms/InstCombine/shuffle_select.ll b/llvm/test/Transforms/InstCombine/shuffle_select.ll
index 63424a1..219d26d 100644 (file)
--- 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:%.*]], <i8 1, i8 1, i8 1, i8 1>
 ; CHECK-NEXT:    [[T1:%.*]] = or <4 x i8> [[V0]], <i8 poison, i8 poison, i8 -64, i8 -64>
-; CHECK-NEXT:    [[T2:%.*]] = add <4 x i8> [[V0]], <i8 1, i8 2, i8 poison, i8 poison>
+; CHECK-NEXT:    [[T2:%.*]] = add nuw nsw <4 x i8> [[V0]], <i8 1, i8 2, i8 poison, i8 poison>
 ; CHECK-NEXT:    [[T3:%.*]] = shufflevector <4 x i8> [[T2]], <4 x i8> [[T1]], <4 x i32> <i32 0, i32 1, i32 6, i32 7>
 ; CHECK-NEXT:    ret <4 x i8> [[T3]]
 ;

diff --git a/llvm/test/Transforms/InstCombine/vec_demanded_elts-inseltpoison.ll b/llvm/test/Transforms/InstCombine/vec_demanded_elts-inseltpoison.ll
index 10d6bed..3a6f95a 100644 (file)
--- a/llvm/test/Transforms/InstCombine/vec_demanded_elts-inseltpoison.ll
+++ b/llvm/test/Transforms/InstCombine/vec_demanded_elts-inseltpoison.ll
@@ -204,7 +204,7 @@ 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 <3 x i8> [[X:%.*]], <i8 poison, i8 2, i8 3>
+; CHECK-NEXT:    [[BO:%.*]] = add nsw <3 x i8> [[X:%.*]], <i8 poison, i8 2, i8 3>
 ; CHECK-NEXT:    [[R:%.*]] = shufflevector <3 x i8> [[BO]], <3 x i8> poison, <3 x i32> <i32 1, i32 undef, i32 2>
 ; CHECK-NEXT:    ret <3 x i8> [[R]]
 ;
@@ -215,7 +215,7 @@ 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 <3 x i8> <i8 1, i8 poison, i8 3>, [[X:%.*]]
+; CHECK-NEXT:    [[BO:%.*]] = sub nuw <3 x i8> <i8 1, i8 poison, i8 3>, [[X:%.*]]
 ; CHECK-NEXT:    [[R:%.*]] = shufflevector <3 x i8> [[BO]], <3 x i8> poison, <3 x i32> <i32 0, i32 undef, i32 2>
 ; CHECK-NEXT:    ret <3 x i8> [[R]]
 ;
@@ -226,7 +226,7 @@ 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 <3 x i8> [[X:%.*]], <i8 1, i8 poison, i8 3>
+; CHECK-NEXT:    [[BO:%.*]] = mul nsw <3 x i8> [[X:%.*]], <i8 1, i8 poison, i8 3>
 ; CHECK-NEXT:    [[R:%.*]] = shufflevector <3 x i8> [[BO]], <3 x i8> poison, <3 x i32> <i32 0, i32 2, i32 0>
 ; CHECK-NEXT:    ret <3 x i8> [[R]]
 ;

diff --git a/llvm/test/Transforms/InstCombine/vec_demanded_elts.ll b/llvm/test/Transforms/InstCombine/vec_demanded_elts.ll
index 7fba4ff..a513d39 100644 (file)
--- a/llvm/test/Transforms/InstCombine/vec_demanded_elts.ll
+++ b/llvm/test/Transforms/InstCombine/vec_demanded_elts.ll
@@ -204,7 +204,7 @@ 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 <3 x i8> [[X:%.*]], <i8 poison, i8 2, i8 3>
+; CHECK-NEXT:    [[BO:%.*]] = add nsw <3 x i8> [[X:%.*]], <i8 poison, i8 2, i8 3>
 ; CHECK-NEXT:    [[R:%.*]] = shufflevector <3 x i8> [[BO]], <3 x i8> undef, <3 x i32> <i32 1, i32 undef, i32 2>
 ; CHECK-NEXT:    ret <3 x i8> [[R]]
 ;
@@ -215,7 +215,7 @@ 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 <3 x i8> <i8 1, i8 poison, i8 3>, [[X:%.*]]
+; CHECK-NEXT:    [[BO:%.*]] = sub nuw <3 x i8> <i8 1, i8 poison, i8 3>, [[X:%.*]]
 ; CHECK-NEXT:    [[R:%.*]] = shufflevector <3 x i8> [[BO]], <3 x i8> undef, <3 x i32> <i32 0, i32 undef, i32 2>
 ; CHECK-NEXT:    ret <3 x i8> [[R]]
 ;
@@ -226,7 +226,7 @@ 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 <3 x i8> [[X:%.*]], <i8 1, i8 poison, i8 3>
+; CHECK-NEXT:    [[BO:%.*]] = mul nsw <3 x i8> [[X:%.*]], <i8 1, i8 poison, i8 3>
 ; CHECK-NEXT:    [[R:%.*]] = shufflevector <3 x i8> [[BO]], <3 x i8> undef, <3 x i32> <i32 0, i32 2, i32 0>
 ; CHECK-NEXT:    ret <3 x i8> [[R]]
 ;