[llvm] r333962 - [InstCombine] refine UB-handling in shuffle-binop transform
Sanjay Patel via llvm-commits
llvm-commits at lists.llvm.org
Mon Jun 4 15:26:45 PDT 2018
Author: spatel
Date: Mon Jun 4 15:26:45 2018
New Revision: 333962
URL: http://llvm.org/viewvc/llvm-project?rev=333962&view=rev
Log:
[InstCombine] refine UB-handling in shuffle-binop transform
As noted in rL333782, we can be both better for optimization and
safer with this transform:
BinOp (shuffle V1, Mask), C --> shuffle (BinOp V1, NewC), Mask
The only potentially unsafe-to-speculate binops are integer div/rem.
All other binops are always safe (although I don't see a way to
assert that in code here).
For opcodes like shifts that can produce poison, it can't matter
here because we know the lanes with undef are dropped by the
subsequent shuffle.
Differential Revision: https://reviews.llvm.org/D47686
Modified:
llvm/trunk/lib/Transforms/InstCombine/InstructionCombining.cpp
llvm/trunk/test/Transforms/InstCombine/vec_shuffle.ll
Modified: llvm/trunk/lib/Transforms/InstCombine/InstructionCombining.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/InstCombine/InstructionCombining.cpp?rev=333962&r1=333961&r2=333962&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/InstCombine/InstructionCombining.cpp (original)
+++ llvm/trunk/lib/Transforms/InstCombine/InstructionCombining.cpp Mon Jun 4 15:26:45 2018
@@ -1417,21 +1417,21 @@ Instruction *InstCombiner::foldShuffledB
}
}
if (MayChange) {
- // It's not safe to use a vector with undef elements because the entire
- // instruction can be folded to undef (for example, div/rem divisors).
- // Replace undef lanes with the first non-undef element. Vector demanded
- // elements can change those back to undef values if that is safe.
- Constant *SafeDummyConstant = nullptr;
- for (unsigned i = 0; i < VWidth; ++i) {
- if (!isa<UndefValue>(NewVecC[i])) {
- SafeDummyConstant = NewVecC[i];
- break;
- }
+ // With integer div/rem instructions, it is not safe to use a vector with
+ // undef elements because the entire instruction can be folded to undef.
+ // So replace undef elements with '1' because that can never induce
+ // undefined behavior. All other binop opcodes are always safe to
+ // speculate, and therefore, it is fine to include undef elements for
+ // unused lanes (and using undefs may help optimization).
+ BinaryOperator::BinaryOps Opcode = Inst.getOpcode();
+ if (Opcode == Instruction::UDiv || Opcode == Instruction::URem ||
+ Opcode == Instruction::SDiv || Opcode == Instruction::SRem) {
+ assert(C->getType()->getScalarType()->isIntegerTy() &&
+ "Not expecting FP opcodes/operands/constants here");
+ for (unsigned i = 0; i < VWidth; ++i)
+ if (isa<UndefValue>(NewVecC[i]))
+ NewVecC[i] = ConstantInt::get(NewVecC[i]->getType(), 1);
}
- assert(SafeDummyConstant && "Undef constant vector was not simplified?");
- for (unsigned i = 0; i < VWidth; ++i)
- if (isa<UndefValue>(NewVecC[i]))
- NewVecC[i] = SafeDummyConstant;
// Op(shuffle(V1, Mask), C) -> shuffle(Op(V1, NewC), Mask)
// Op(C, shuffle(V1, Mask)) -> shuffle(Op(NewC, V1), Mask)
Modified: llvm/trunk/test/Transforms/InstCombine/vec_shuffle.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/vec_shuffle.ll?rev=333962&r1=333961&r2=333962&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/InstCombine/vec_shuffle.ll (original)
+++ llvm/trunk/test/Transforms/InstCombine/vec_shuffle.ll Mon Jun 4 15:26:45 2018
@@ -452,7 +452,7 @@ define <4 x i32> @mul_const_splat(<4 x i
define <4 x i32> @lshr_const_half_splat(<4 x i32> %v) {
; CHECK-LABEL: @lshr_const_half_splat(
-; CHECK-NEXT: [[TMP1:%.*]] = lshr <4 x i32> <i32 8, i32 8, i32 9, i32 8>, [[V:%.*]]
+; CHECK-NEXT: [[TMP1:%.*]] = lshr <4 x i32> <i32 undef, i32 8, i32 9, i32 undef>, [[V:%.*]]
; CHECK-NEXT: [[R:%.*]] = shufflevector <4 x i32> [[TMP1]], <4 x i32> undef, <4 x i32> <i32 1, i32 1, i32 2, i32 2>
; CHECK-NEXT: ret <4 x i32> [[R]]
;
@@ -643,7 +643,7 @@ define <2 x i32> @mul_splat_constant(<2
define <2 x i32> @shl_splat_constant0(<2 x i32> %x) {
; CHECK-LABEL: @shl_splat_constant0(
-; CHECK-NEXT: [[TMP1:%.*]] = shl <2 x i32> <i32 5, i32 5>, [[X:%.*]]
+; CHECK-NEXT: [[TMP1:%.*]] = shl <2 x i32> <i32 5, i32 undef>, [[X:%.*]]
; CHECK-NEXT: [[R:%.*]] = shufflevector <2 x i32> [[TMP1]], <2 x i32> undef, <2 x i32> zeroinitializer
; CHECK-NEXT: ret <2 x i32> [[R]]
;
@@ -654,7 +654,7 @@ define <2 x i32> @shl_splat_constant0(<2
define <2 x i32> @shl_splat_constant1(<2 x i32> %x) {
; CHECK-LABEL: @shl_splat_constant1(
-; CHECK-NEXT: [[TMP1:%.*]] = shl <2 x i32> [[X:%.*]], <i32 5, i32 5>
+; CHECK-NEXT: [[TMP1:%.*]] = shl <2 x i32> [[X:%.*]], <i32 5, i32 undef>
; CHECK-NEXT: [[R:%.*]] = shufflevector <2 x i32> [[TMP1]], <2 x i32> undef, <2 x i32> zeroinitializer
; CHECK-NEXT: ret <2 x i32> [[R]]
;
@@ -665,7 +665,7 @@ define <2 x i32> @shl_splat_constant1(<2
define <2 x i32> @ashr_splat_constant0(<2 x i32> %x) {
; CHECK-LABEL: @ashr_splat_constant0(
-; CHECK-NEXT: [[TMP1:%.*]] = lshr <2 x i32> <i32 5, i32 5>, [[X:%.*]]
+; CHECK-NEXT: [[TMP1:%.*]] = ashr <2 x i32> <i32 5, i32 undef>, [[X:%.*]]
; CHECK-NEXT: [[R:%.*]] = shufflevector <2 x i32> [[TMP1]], <2 x i32> undef, <2 x i32> zeroinitializer
; CHECK-NEXT: ret <2 x i32> [[R]]
;
@@ -676,7 +676,7 @@ define <2 x i32> @ashr_splat_constant0(<
define <2 x i32> @ashr_splat_constant1(<2 x i32> %x) {
; CHECK-LABEL: @ashr_splat_constant1(
-; CHECK-NEXT: [[TMP1:%.*]] = ashr <2 x i32> [[X:%.*]], <i32 5, i32 5>
+; CHECK-NEXT: [[TMP1:%.*]] = ashr <2 x i32> [[X:%.*]], <i32 5, i32 undef>
; CHECK-NEXT: [[R:%.*]] = shufflevector <2 x i32> [[TMP1]], <2 x i32> undef, <2 x i32> zeroinitializer
; CHECK-NEXT: ret <2 x i32> [[R]]
;
@@ -687,7 +687,7 @@ define <2 x i32> @ashr_splat_constant1(<
define <2 x i32> @lshr_splat_constant0(<2 x i32> %x) {
; CHECK-LABEL: @lshr_splat_constant0(
-; CHECK-NEXT: [[TMP1:%.*]] = lshr <2 x i32> <i32 5, i32 5>, [[X:%.*]]
+; CHECK-NEXT: [[TMP1:%.*]] = lshr <2 x i32> <i32 5, i32 undef>, [[X:%.*]]
; CHECK-NEXT: [[R:%.*]] = shufflevector <2 x i32> [[TMP1]], <2 x i32> undef, <2 x i32> zeroinitializer
; CHECK-NEXT: ret <2 x i32> [[R]]
;
@@ -698,7 +698,7 @@ define <2 x i32> @lshr_splat_constant0(<
define <2 x i32> @lshr_splat_constant1(<2 x i32> %x) {
; CHECK-LABEL: @lshr_splat_constant1(
-; CHECK-NEXT: [[TMP1:%.*]] = lshr <2 x i32> [[X:%.*]], <i32 5, i32 5>
+; CHECK-NEXT: [[TMP1:%.*]] = lshr <2 x i32> [[X:%.*]], <i32 5, i32 undef>
; CHECK-NEXT: [[R:%.*]] = shufflevector <2 x i32> [[TMP1]], <2 x i32> undef, <2 x i32> zeroinitializer
; CHECK-NEXT: ret <2 x i32> [[R]]
;
@@ -720,7 +720,7 @@ define <2 x i32> @urem_splat_constant0(<
define <2 x i32> @urem_splat_constant1(<2 x i32> %x) {
; CHECK-LABEL: @urem_splat_constant1(
-; CHECK-NEXT: [[TMP1:%.*]] = urem <2 x i32> [[X:%.*]], <i32 42, i32 42>
+; CHECK-NEXT: [[TMP1:%.*]] = urem <2 x i32> [[X:%.*]], <i32 42, i32 1>
; CHECK-NEXT: [[R:%.*]] = shufflevector <2 x i32> [[TMP1]], <2 x i32> undef, <2 x i32> zeroinitializer
; CHECK-NEXT: ret <2 x i32> [[R]]
;
@@ -742,7 +742,7 @@ define <2 x i32> @srem_splat_constant0(<
define <2 x i32> @srem_splat_constant1(<2 x i32> %x) {
; CHECK-LABEL: @srem_splat_constant1(
-; CHECK-NEXT: [[TMP1:%.*]] = srem <2 x i32> [[X:%.*]], <i32 42, i32 42>
+; CHECK-NEXT: [[TMP1:%.*]] = srem <2 x i32> [[X:%.*]], <i32 42, i32 1>
; CHECK-NEXT: [[R:%.*]] = shufflevector <2 x i32> [[TMP1]], <2 x i32> undef, <2 x i32> zeroinitializer
; CHECK-NEXT: ret <2 x i32> [[R]]
;
@@ -764,7 +764,7 @@ define <2 x i32> @udiv_splat_constant0(<
define <2 x i32> @udiv_splat_constant1(<2 x i32> %x) {
; CHECK-LABEL: @udiv_splat_constant1(
-; CHECK-NEXT: [[TMP1:%.*]] = udiv <2 x i32> [[X:%.*]], <i32 42, i32 42>
+; CHECK-NEXT: [[TMP1:%.*]] = udiv <2 x i32> [[X:%.*]], <i32 42, i32 1>
; CHECK-NEXT: [[R:%.*]] = shufflevector <2 x i32> [[TMP1]], <2 x i32> undef, <2 x i32> zeroinitializer
; CHECK-NEXT: ret <2 x i32> [[R]]
;
@@ -786,7 +786,7 @@ define <2 x i32> @sdiv_splat_constant0(<
define <2 x i32> @sdiv_splat_constant1(<2 x i32> %x) {
; CHECK-LABEL: @sdiv_splat_constant1(
-; CHECK-NEXT: [[TMP1:%.*]] = sdiv <2 x i32> [[X:%.*]], <i32 42, i32 42>
+; CHECK-NEXT: [[TMP1:%.*]] = sdiv <2 x i32> [[X:%.*]], <i32 42, i32 1>
; CHECK-NEXT: [[R:%.*]] = shufflevector <2 x i32> [[TMP1]], <2 x i32> undef, <2 x i32> zeroinitializer
; CHECK-NEXT: ret <2 x i32> [[R]]
;
@@ -830,7 +830,7 @@ define <2 x i32> @xor_splat_constant(<2
define <2 x float> @fadd_splat_constant(<2 x float> %x) {
; CHECK-LABEL: @fadd_splat_constant(
-; CHECK-NEXT: [[TMP1:%.*]] = fadd <2 x float> [[X:%.*]], <float 4.200000e+01, float 4.200000e+01>
+; CHECK-NEXT: [[TMP1:%.*]] = fadd <2 x float> [[X:%.*]], <float 4.200000e+01, float undef>
; CHECK-NEXT: [[R:%.*]] = shufflevector <2 x float> [[TMP1]], <2 x float> undef, <2 x i32> zeroinitializer
; CHECK-NEXT: ret <2 x float> [[R]]
;
@@ -841,7 +841,7 @@ define <2 x float> @fadd_splat_constant(
define <2 x float> @fsub_splat_constant0(<2 x float> %x) {
; CHECK-LABEL: @fsub_splat_constant0(
-; CHECK-NEXT: [[TMP1:%.*]] = fsub <2 x float> <float 4.200000e+01, float 4.200000e+01>, [[X:%.*]]
+; CHECK-NEXT: [[TMP1:%.*]] = fsub <2 x float> <float 4.200000e+01, float undef>, [[X:%.*]]
; CHECK-NEXT: [[R:%.*]] = shufflevector <2 x float> [[TMP1]], <2 x float> undef, <2 x i32> zeroinitializer
; CHECK-NEXT: ret <2 x float> [[R]]
;
@@ -852,7 +852,7 @@ define <2 x float> @fsub_splat_constant0
define <2 x float> @fsub_splat_constant1(<2 x float> %x) {
; CHECK-LABEL: @fsub_splat_constant1(
-; CHECK-NEXT: [[TMP1:%.*]] = fadd <2 x float> [[X:%.*]], <float -4.200000e+01, float -4.200000e+01>
+; CHECK-NEXT: [[TMP1:%.*]] = fadd <2 x float> [[X:%.*]], <float -4.200000e+01, float 0x7FF8000000000000>
; CHECK-NEXT: [[R:%.*]] = shufflevector <2 x float> [[TMP1]], <2 x float> undef, <2 x i32> zeroinitializer
; CHECK-NEXT: ret <2 x float> [[R]]
;
@@ -863,7 +863,7 @@ define <2 x float> @fsub_splat_constant1
define <2 x float> @fmul_splat_constant(<2 x float> %x) {
; CHECK-LABEL: @fmul_splat_constant(
-; CHECK-NEXT: [[TMP1:%.*]] = fmul <2 x float> [[X:%.*]], <float 4.200000e+01, float 4.200000e+01>
+; CHECK-NEXT: [[TMP1:%.*]] = fmul <2 x float> [[X:%.*]], <float 4.200000e+01, float undef>
; CHECK-NEXT: [[R:%.*]] = shufflevector <2 x float> [[TMP1]], <2 x float> undef, <2 x i32> zeroinitializer
; CHECK-NEXT: ret <2 x float> [[R]]
;
@@ -874,7 +874,7 @@ define <2 x float> @fmul_splat_constant(
define <2 x float> @fdiv_splat_constant0(<2 x float> %x) {
; CHECK-LABEL: @fdiv_splat_constant0(
-; CHECK-NEXT: [[TMP1:%.*]] = fdiv <2 x float> <float 4.200000e+01, float 4.200000e+01>, [[X:%.*]]
+; CHECK-NEXT: [[TMP1:%.*]] = fdiv <2 x float> <float 4.200000e+01, float undef>, [[X:%.*]]
; CHECK-NEXT: [[R:%.*]] = shufflevector <2 x float> [[TMP1]], <2 x float> undef, <2 x i32> zeroinitializer
; CHECK-NEXT: ret <2 x float> [[R]]
;
@@ -885,7 +885,7 @@ define <2 x float> @fdiv_splat_constant0
define <2 x float> @fdiv_splat_constant1(<2 x float> %x) {
; CHECK-LABEL: @fdiv_splat_constant1(
-; CHECK-NEXT: [[TMP1:%.*]] = fdiv <2 x float> [[X:%.*]], <float 4.200000e+01, float 4.200000e+01>
+; CHECK-NEXT: [[TMP1:%.*]] = fdiv <2 x float> [[X:%.*]], <float 4.200000e+01, float undef>
; CHECK-NEXT: [[R:%.*]] = shufflevector <2 x float> [[TMP1]], <2 x float> undef, <2 x i32> zeroinitializer
; CHECK-NEXT: ret <2 x float> [[R]]
;
@@ -896,7 +896,7 @@ define <2 x float> @fdiv_splat_constant1
define <2 x float> @frem_splat_constant0(<2 x float> %x) {
; CHECK-LABEL: @frem_splat_constant0(
-; CHECK-NEXT: [[TMP1:%.*]] = frem <2 x float> <float 4.200000e+01, float 4.200000e+01>, [[X:%.*]]
+; CHECK-NEXT: [[TMP1:%.*]] = frem <2 x float> <float 4.200000e+01, float undef>, [[X:%.*]]
; CHECK-NEXT: [[R:%.*]] = shufflevector <2 x float> [[TMP1]], <2 x float> undef, <2 x i32> zeroinitializer
; CHECK-NEXT: ret <2 x float> [[R]]
;
@@ -907,7 +907,7 @@ define <2 x float> @frem_splat_constant0
define <2 x float> @frem_splat_constant1(<2 x float> %x) {
; CHECK-LABEL: @frem_splat_constant1(
-; CHECK-NEXT: [[TMP1:%.*]] = frem <2 x float> [[X:%.*]], <float 4.200000e+01, float 4.200000e+01>
+; CHECK-NEXT: [[TMP1:%.*]] = frem <2 x float> [[X:%.*]], <float 4.200000e+01, float undef>
; CHECK-NEXT: [[R:%.*]] = shufflevector <2 x float> [[TMP1]], <2 x float> undef, <2 x i32> zeroinitializer
; CHECK-NEXT: ret <2 x float> [[R]]
;
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