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Revert "[InstSimplify] Remove select ?, undef, X -> X and select ?, X…
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…, undef -> X transforms" and subsequent patches

This reverts most of the following patches due to reports of miscompiles.
I've left the added test cases with comments updated to be FIXMEs.

1cf6f21 [IR] Disable select ? C : undef -> C fold in ConstantFoldSelectInstruction unless we know C isn't poison.
469da66 [InstSimplify] Re-enable select ?, undef, X -> X transform when X is provably not poison
122b064 [InstSimplify] Don't fold vectors of partial undef in SimplifySelectInst if the non-undef element value might produce poison
ac0af12 [InstSimplify] Add test cases for opportunities to fold select ?, X, undef -> X when we can prove X isn't poison
9b1e953 [InstSimplify] Remove select ?, undef, X -> X and select ?, X, undef -> X transforms

(cherry picked from commit 00f3579)
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@topperc @zmodem
topperc authored and zmodem committed Jul 16, 2020
1 parent 15a07e4 commit 529f2e0
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Showing 6 changed files with 33 additions and 82 deletions.
24 changes: 8 additions & 16 deletions clang/test/CodeGen/arm-mve-intrinsics/dup.c
View file
Expand Up @@ -242,8 +242,7 @@ uint32x4_t test_vdupq_m_n_u32(uint32x4_t inactive, uint32_t a, mve_pred16_t p)
// CHECK-NEXT: [[TMP1:%.*]] = call <8 x i1> @llvm.arm.mve.pred.i2v.v8i1(i32 [[TMP0]])
// CHECK-NEXT: [[DOTSPLATINSERT:%.*]] = insertelement <8 x half> undef, half [[A:%.*]], i32 0
// CHECK-NEXT: [[DOTSPLAT:%.*]] = shufflevector <8 x half> [[DOTSPLATINSERT]], <8 x half> undef, <8 x i32> zeroinitializer
// CHECK-NEXT: [[TMP2:%.*]] = select <8 x i1> [[TMP1]], <8 x half> [[DOTSPLAT]], <8 x half> undef
// CHECK-NEXT: ret <8 x half> [[TMP2]]
// CHECK-NEXT: ret <8 x half> [[DOTSPLAT]]
//
float16x8_t test_vdupq_x_n_f16(float16_t a, mve_pred16_t p)
{
Expand All @@ -256,8 +255,7 @@ float16x8_t test_vdupq_x_n_f16(float16_t a, mve_pred16_t p)
// CHECK-NEXT: [[TMP1:%.*]] = call <4 x i1> @llvm.arm.mve.pred.i2v.v4i1(i32 [[TMP0]])
// CHECK-NEXT: [[DOTSPLATINSERT:%.*]] = insertelement <4 x float> undef, float [[A:%.*]], i32 0
// CHECK-NEXT: [[DOTSPLAT:%.*]] = shufflevector <4 x float> [[DOTSPLATINSERT]], <4 x float> undef, <4 x i32> zeroinitializer
// CHECK-NEXT: [[TMP2:%.*]] = select <4 x i1> [[TMP1]], <4 x float> [[DOTSPLAT]], <4 x float> undef
// CHECK-NEXT: ret <4 x float> [[TMP2]]
// CHECK-NEXT: ret <4 x float> [[DOTSPLAT]]
//
float32x4_t test_vdupq_x_n_f32(float32_t a, mve_pred16_t p)
{
Expand All @@ -270,8 +268,7 @@ float32x4_t test_vdupq_x_n_f32(float32_t a, mve_pred16_t p)
// CHECK-NEXT: [[TMP1:%.*]] = call <16 x i1> @llvm.arm.mve.pred.i2v.v16i1(i32 [[TMP0]])
// CHECK-NEXT: [[DOTSPLATINSERT:%.*]] = insertelement <16 x i8> undef, i8 [[A:%.*]], i32 0
// CHECK-NEXT: [[DOTSPLAT:%.*]] = shufflevector <16 x i8> [[DOTSPLATINSERT]], <16 x i8> undef, <16 x i32> zeroinitializer
// CHECK-NEXT: [[TMP2:%.*]] = select <16 x i1> [[TMP1]], <16 x i8> [[DOTSPLAT]], <16 x i8> undef
// CHECK-NEXT: ret <16 x i8> [[TMP2]]
// CHECK-NEXT: ret <16 x i8> [[DOTSPLAT]]
//
int8x16_t test_vdupq_x_n_s8(int8_t a, mve_pred16_t p)
{
Expand All @@ -284,8 +281,7 @@ int8x16_t test_vdupq_x_n_s8(int8_t a, mve_pred16_t p)
// CHECK-NEXT: [[TMP1:%.*]] = call <8 x i1> @llvm.arm.mve.pred.i2v.v8i1(i32 [[TMP0]])
// CHECK-NEXT: [[DOTSPLATINSERT:%.*]] = insertelement <8 x i16> undef, i16 [[A:%.*]], i32 0
// CHECK-NEXT: [[DOTSPLAT:%.*]] = shufflevector <8 x i16> [[DOTSPLATINSERT]], <8 x i16> undef, <8 x i32> zeroinitializer
// CHECK-NEXT: [[TMP2:%.*]] = select <8 x i1> [[TMP1]], <8 x i16> [[DOTSPLAT]], <8 x i16> undef
// CHECK-NEXT: ret <8 x i16> [[TMP2]]
// CHECK-NEXT: ret <8 x i16> [[DOTSPLAT]]
//
int16x8_t test_vdupq_x_n_s16(int16_t a, mve_pred16_t p)
{
Expand All @@ -298,8 +294,7 @@ int16x8_t test_vdupq_x_n_s16(int16_t a, mve_pred16_t p)
// CHECK-NEXT: [[TMP1:%.*]] = call <4 x i1> @llvm.arm.mve.pred.i2v.v4i1(i32 [[TMP0]])
// CHECK-NEXT: [[DOTSPLATINSERT:%.*]] = insertelement <4 x i32> undef, i32 [[A:%.*]], i32 0
// CHECK-NEXT: [[DOTSPLAT:%.*]] = shufflevector <4 x i32> [[DOTSPLATINSERT]], <4 x i32> undef, <4 x i32> zeroinitializer
// CHECK-NEXT: [[TMP2:%.*]] = select <4 x i1> [[TMP1]], <4 x i32> [[DOTSPLAT]], <4 x i32> undef
// CHECK-NEXT: ret <4 x i32> [[TMP2]]
// CHECK-NEXT: ret <4 x i32> [[DOTSPLAT]]
//
int32x4_t test_vdupq_x_n_s32(int32_t a, mve_pred16_t p)
{
Expand All @@ -312,8 +307,7 @@ int32x4_t test_vdupq_x_n_s32(int32_t a, mve_pred16_t p)
// CHECK-NEXT: [[TMP1:%.*]] = call <16 x i1> @llvm.arm.mve.pred.i2v.v16i1(i32 [[TMP0]])
// CHECK-NEXT: [[DOTSPLATINSERT:%.*]] = insertelement <16 x i8> undef, i8 [[A:%.*]], i32 0
// CHECK-NEXT: [[DOTSPLAT:%.*]] = shufflevector <16 x i8> [[DOTSPLATINSERT]], <16 x i8> undef, <16 x i32> zeroinitializer
// CHECK-NEXT: [[TMP2:%.*]] = select <16 x i1> [[TMP1]], <16 x i8> [[DOTSPLAT]], <16 x i8> undef
// CHECK-NEXT: ret <16 x i8> [[TMP2]]
// CHECK-NEXT: ret <16 x i8> [[DOTSPLAT]]
//
uint8x16_t test_vdupq_x_n_u8(uint8_t a, mve_pred16_t p)
{
Expand All @@ -326,8 +320,7 @@ uint8x16_t test_vdupq_x_n_u8(uint8_t a, mve_pred16_t p)
// CHECK-NEXT: [[TMP1:%.*]] = call <8 x i1> @llvm.arm.mve.pred.i2v.v8i1(i32 [[TMP0]])
// CHECK-NEXT: [[DOTSPLATINSERT:%.*]] = insertelement <8 x i16> undef, i16 [[A:%.*]], i32 0
// CHECK-NEXT: [[DOTSPLAT:%.*]] = shufflevector <8 x i16> [[DOTSPLATINSERT]], <8 x i16> undef, <8 x i32> zeroinitializer
// CHECK-NEXT: [[TMP2:%.*]] = select <8 x i1> [[TMP1]], <8 x i16> [[DOTSPLAT]], <8 x i16> undef
// CHECK-NEXT: ret <8 x i16> [[TMP2]]
// CHECK-NEXT: ret <8 x i16> [[DOTSPLAT]]
//
uint16x8_t test_vdupq_x_n_u16(uint16_t a, mve_pred16_t p)
{
Expand All @@ -340,8 +333,7 @@ uint16x8_t test_vdupq_x_n_u16(uint16_t a, mve_pred16_t p)
// CHECK-NEXT: [[TMP1:%.*]] = call <4 x i1> @llvm.arm.mve.pred.i2v.v4i1(i32 [[TMP0]])
// CHECK-NEXT: [[DOTSPLATINSERT:%.*]] = insertelement <4 x i32> undef, i32 [[A:%.*]], i32 0
// CHECK-NEXT: [[DOTSPLAT:%.*]] = shufflevector <4 x i32> [[DOTSPLATINSERT]], <4 x i32> undef, <4 x i32> zeroinitializer
// CHECK-NEXT: [[TMP2:%.*]] = select <4 x i1> [[TMP1]], <4 x i32> [[DOTSPLAT]], <4 x i32> undef
// CHECK-NEXT: ret <4 x i32> [[TMP2]]
// CHECK-NEXT: ret <4 x i32> [[DOTSPLAT]]
//
uint32x4_t test_vdupq_x_n_u32(uint32_t a, mve_pred16_t p)
{
Expand Down
16 changes: 4 additions & 12 deletions llvm/lib/Analysis/InstructionSimplify.cpp
View file
Expand Up @@ -4118,15 +4118,9 @@ static Value *SimplifySelectInst(Value *Cond, Value *TrueVal, Value *FalseVal,
if (TrueVal == FalseVal)
return TrueVal;

// If the true or false value is undef, we can fold to the other value as
// long as the other value isn't poison.
// select ?, undef, X -> X
if (isa<UndefValue>(TrueVal) &&
isGuaranteedNotToBeUndefOrPoison(FalseVal, Q.CxtI, Q.DT))
if (isa<UndefValue>(TrueVal)) // select ?, undef, X -> X
return FalseVal;
// select ?, X, undef -> X
if (isa<UndefValue>(FalseVal) &&
isGuaranteedNotToBeUndefOrPoison(TrueVal, Q.CxtI, Q.DT))
if (isa<UndefValue>(FalseVal)) // select ?, X, undef -> X
return TrueVal;

// Deal with partial undef vector constants: select ?, VecC, VecC' --> VecC''
Expand All @@ -4146,11 +4140,9 @@ static Value *SimplifySelectInst(Value *Cond, Value *TrueVal, Value *FalseVal,
// one element is undef, choose the defined element as the safe result.
if (TEltC == FEltC)
NewC.push_back(TEltC);
else if (isa<UndefValue>(TEltC) &&
isGuaranteedNotToBeUndefOrPoison(FEltC))
else if (isa<UndefValue>(TEltC))
NewC.push_back(FEltC);
else if (isa<UndefValue>(FEltC) &&
isGuaranteedNotToBeUndefOrPoison(TEltC))
else if (isa<UndefValue>(FEltC))
NewC.push_back(TEltC);
else
break;
Expand Down
24 changes: 2 additions & 22 deletions llvm/lib/IR/ConstantFold.cpp
View file
Expand Up @@ -779,30 +779,10 @@ Constant *llvm::ConstantFoldSelectInstruction(Constant *Cond,
if (isa<UndefValue>(V1)) return V1;
return V2;
}

if (isa<UndefValue>(V1)) return V2;
if (isa<UndefValue>(V2)) return V1;
if (V1 == V2) return V1;

// If the true or false value is undef, we can fold to the other value as
// long as the other value isn't poison.
auto NotPoison = [](Constant *C) {
// TODO: We can analyze ConstExpr by opcode to determine if there is any
// possibility of poison.
if (isa<ConstantExpr>(C))
return false;

if (isa<ConstantInt>(C) || isa<GlobalVariable>(C) || isa<ConstantFP>(C) ||
isa<ConstantPointerNull>(C) || isa<Function>(C))
return true;

if (C->getType()->isVectorTy())
return !C->containsUndefElement() && !C->containsConstantExpression();

// TODO: Recursively analyze aggregates or other constants.
return false;
};
if (isa<UndefValue>(V1) && NotPoison(V2)) return V2;
if (isa<UndefValue>(V2) && NotPoison(V1)) return V1;

if (ConstantExpr *TrueVal = dyn_cast<ConstantExpr>(V1)) {
if (TrueVal->getOpcode() == Instruction::Select)
if (TrueVal->getOperand(0) == Cond)
Expand Down
2 changes: 1 addition & 1 deletion llvm/test/Transforms/InferAddressSpaces/AMDGPU/select.ll
View file
Expand Up @@ -221,7 +221,7 @@ define amdgpu_kernel void @store_select_group_global_mismatch_inttoptr_flat_null
}

; CHECK-LABEL: @store_select_group_global_mismatch_undef_undef_constexpr(
; CHECK: store i32 7, i32* select (i1 icmp eq (i32 ptrtoint (i32 addrspace(3)* @lds1 to i32), i32 4), i32* addrspacecast (i32 addrspace(3)* null to i32*), i32* undef), align 4
; CHECK: store i32 7, i32 addrspace(3)* null
define amdgpu_kernel void @store_select_group_global_mismatch_undef_undef_constexpr() #0 {
store i32 7, i32* select (i1 icmp eq (i32 ptrtoint (i32 addrspace(3)* @lds1 to i32), i32 4), i32* addrspacecast (i32 addrspace(3)* null to i32*), i32* addrspacecast (i32 addrspace(1)* undef to i32*)), align 4
ret void
Expand Down
14 changes: 5 additions & 9 deletions llvm/test/Transforms/InstCombine/select.ll
View file
Expand Up @@ -2437,41 +2437,37 @@ exit:
ret i32 %sel
}

; Negative tests to ensure we don't remove selects with undef true/false values.
; FIXME: We shouldn't remove selects with undef true/false values.
; See https://bugs.llvm.org/show_bug.cgi?id=31633
; https://lists.llvm.org/pipermail/llvm-dev/2016-October/106182.html
; https://reviews.llvm.org/D83360
define i32 @false_undef(i1 %cond, i32 %x) {
; CHECK-LABEL: @false_undef(
; CHECK-NEXT: [[S:%.*]] = select i1 [[COND:%.*]], i32 [[X:%.*]], i32 undef
; CHECK-NEXT: ret i32 [[S]]
; CHECK-NEXT: ret i32 [[X:%.*]]
;
%s = select i1 %cond, i32 %x, i32 undef
ret i32 %s
}

define i32 @true_undef(i1 %cond, i32 %x) {
; CHECK-LABEL: @true_undef(
; CHECK-NEXT: [[S:%.*]] = select i1 [[COND:%.*]], i32 undef, i32 [[X:%.*]]
; CHECK-NEXT: ret i32 [[S]]
; CHECK-NEXT: ret i32 [[X:%.*]]
;
%s = select i1 %cond, i32 undef, i32 %x
ret i32 %s
}

define <2 x i32> @false_undef_vec(i1 %cond, <2 x i32> %x) {
; CHECK-LABEL: @false_undef_vec(
; CHECK-NEXT: [[S:%.*]] = select i1 [[COND:%.*]], <2 x i32> [[X:%.*]], <2 x i32> undef
; CHECK-NEXT: ret <2 x i32> [[S]]
; CHECK-NEXT: ret <2 x i32> [[X:%.*]]
;
%s = select i1 %cond, <2 x i32> %x, <2 x i32> undef
ret <2 x i32> %s
}

define <2 x i32> @true_undef_vec(i1 %cond, <2 x i32> %x) {
; CHECK-LABEL: @true_undef_vec(
; CHECK-NEXT: [[S:%.*]] = select i1 [[COND:%.*]], <2 x i32> undef, <2 x i32> [[X:%.*]]
; CHECK-NEXT: ret <2 x i32> [[S]]
; CHECK-NEXT: ret <2 x i32> [[X:%.*]]
;
%s = select i1 %cond, <2 x i32> undef, <2 x i32> %x
ret <2 x i32> %s
Expand Down
35 changes: 13 additions & 22 deletions llvm/test/Transforms/InstSimplify/select.ll
View file
Expand Up @@ -751,41 +751,37 @@ define i1 @y_might_be_poison(float %x, float %y) {
ret i1 %c3
}

; Negative tests to ensure we don't remove selects with undef true/false values.
; FIXME: We shouldn't remove selects with undef true/false values.
; See https://bugs.llvm.org/show_bug.cgi?id=31633
; https://lists.llvm.org/pipermail/llvm-dev/2016-October/106182.html
; https://reviews.llvm.org/D83360
define i32 @false_undef(i1 %cond, i32 %x) {
; CHECK-LABEL: @false_undef(
; CHECK-NEXT: [[S:%.*]] = select i1 [[COND:%.*]], i32 [[X:%.*]], i32 undef
; CHECK-NEXT: ret i32 [[S]]
; CHECK-NEXT: ret i32 [[X:%.*]]
;
%s = select i1 %cond, i32 %x, i32 undef
ret i32 %s
}

define i32 @true_undef(i1 %cond, i32 %x) {
; CHECK-LABEL: @true_undef(
; CHECK-NEXT: [[S:%.*]] = select i1 [[COND:%.*]], i32 undef, i32 [[X:%.*]]
; CHECK-NEXT: ret i32 [[S]]
; CHECK-NEXT: ret i32 [[X:%.*]]
;
%s = select i1 %cond, i32 undef, i32 %x
ret i32 %s
}

define <2 x i32> @false_undef_vec(i1 %cond, <2 x i32> %x) {
; CHECK-LABEL: @false_undef_vec(
; CHECK-NEXT: [[S:%.*]] = select i1 [[COND:%.*]], <2 x i32> [[X:%.*]], <2 x i32> undef
; CHECK-NEXT: ret <2 x i32> [[S]]
; CHECK-NEXT: ret <2 x i32> [[X:%.*]]
;
%s = select i1 %cond, <2 x i32> %x, <2 x i32> undef
ret <2 x i32> %s
}

define <2 x i32> @true_undef_vec(i1 %cond, <2 x i32> %x) {
; CHECK-LABEL: @true_undef_vec(
; CHECK-NEXT: [[S:%.*]] = select i1 [[COND:%.*]], <2 x i32> undef, <2 x i32> [[X:%.*]]
; CHECK-NEXT: ret <2 x i32> [[S]]
; CHECK-NEXT: ret <2 x i32> [[X:%.*]]
;
%s = select i1 %cond, <2 x i32> undef, <2 x i32> %x
ret <2 x i32> %s
Expand Down Expand Up @@ -847,13 +843,12 @@ define i32 @false_undef_false_freeze(i1 %cond, i32 %x) {

@g = external global i32, align 1

; Make sure we don't fold partial undef vectors when constexprs are involved.
; FIXME: We shouldn't fold partial undef vectors when constexprs are involved.
; We would need to prove the constexpr doesn't result in poison which we aren't
; equiped to do yet.
define <2 x i32> @false_undef_true_constextpr_vec(i1 %cond) {
; CHECK-LABEL: @false_undef_true_constextpr_vec(
; CHECK-NEXT: [[S:%.*]] = select i1 [[COND:%.*]], <2 x i32> <i32 undef, i32 ptrtoint (i32* @g to i32)>, <2 x i32> <i32 ptrtoint (i32* @g to i32), i32 undef>
; CHECK-NEXT: ret <2 x i32> [[S]]
; CHECK-NEXT: ret <2 x i32> <i32 ptrtoint (i32* @g to i32), i32 ptrtoint (i32* @g to i32)>
;
%s = select i1 %cond, <2 x i32> <i32 undef, i32 ptrtoint (i32* @g to i32)>, <2 x i32> <i32 ptrtoint (i32* @g to i32), i32 undef>
ret <2 x i32> %s
Expand Down Expand Up @@ -891,39 +886,35 @@ define <2 x float> @all_constant_false_undef_vec() {
ret <2 x float> %s
}

; Negative tests. Don't fold if the non-undef operand is a constexpr.
; FIXME: We shouldn't fold if the non-undef operand is a constexpr.
define i32 @all_constant_false_undef_true_constexpr() {
; CHECK-LABEL: @all_constant_false_undef_true_constexpr(
; CHECK-NEXT: [[S:%.*]] = select i1 ptrtoint (i32 ()* @all_constant_false_undef_true_constexpr to i1), i32 ptrtoint (i32 ()* @all_constant_false_undef_true_constexpr to i32), i32 undef
; CHECK-NEXT: ret i32 [[S]]
; CHECK-NEXT: ret i32 ptrtoint (i32 ()* @all_constant_false_undef_true_constexpr to i32)
;
%s = select i1 ptrtoint (i32 ()* @all_constant_false_undef_true_constexpr to i1), i32 ptrtoint (i32 ()* @all_constant_false_undef_true_constexpr to i32), i32 undef
ret i32 %s
}

define i32 @all_constant_true_undef_false_constexpr() {
; CHECK-LABEL: @all_constant_true_undef_false_constexpr(
; CHECK-NEXT: [[S:%.*]] = select i1 ptrtoint (i32 ()* @all_constant_true_undef_false_constexpr to i1), i32 undef, i32 ptrtoint (i32 ()* @all_constant_true_undef_false_constexpr to i32)
; CHECK-NEXT: ret i32 [[S]]
; CHECK-NEXT: ret i32 ptrtoint (i32 ()* @all_constant_true_undef_false_constexpr to i32)
;
%s = select i1 ptrtoint (i32 ()* @all_constant_true_undef_false_constexpr to i1), i32 undef, i32 ptrtoint (i32 ()* @all_constant_true_undef_false_constexpr to i32)
ret i32 %s
}

; Negative tests. Don't fold if the non-undef operand is a vector containing a constexpr.
; FIXME: We shouldn't fold if the non-undef operand is a vector containing a constexpr.
define <2 x i32> @all_constant_false_undef_true_constexpr_vec() {
; CHECK-LABEL: @all_constant_false_undef_true_constexpr_vec(
; CHECK-NEXT: [[S:%.*]] = select i1 ptrtoint (<2 x i32> ()* @all_constant_false_undef_true_constexpr_vec to i1), <2 x i32> <i32 ptrtoint (<2 x i32> ()* @all_constant_false_undef_true_constexpr_vec to i32), i32 -1>, <2 x i32> undef
; CHECK-NEXT: ret <2 x i32> [[S]]
; CHECK-NEXT: ret <2 x i32> <i32 ptrtoint (<2 x i32> ()* @all_constant_false_undef_true_constexpr_vec to i32), i32 -1>
;
%s = select i1 ptrtoint (<2 x i32> ()* @all_constant_false_undef_true_constexpr_vec to i1), <2 x i32> <i32 ptrtoint (<2 x i32> ()* @all_constant_false_undef_true_constexpr_vec to i32), i32 -1>, <2 x i32> undef
ret <2 x i32> %s
}

define <2 x i32> @all_constant_true_undef_false_constexpr_vec() {
; CHECK-LABEL: @all_constant_true_undef_false_constexpr_vec(
; CHECK-NEXT: [[S:%.*]] = select i1 ptrtoint (<2 x i32> ()* @all_constant_true_undef_false_constexpr_vec to i1), <2 x i32> undef, <2 x i32> <i32 -1, i32 ptrtoint (<2 x i32> ()* @all_constant_true_undef_false_constexpr_vec to i32)>
; CHECK-NEXT: ret <2 x i32> [[S]]
; CHECK-NEXT: ret <2 x i32> <i32 -1, i32 ptrtoint (<2 x i32> ()* @all_constant_true_undef_false_constexpr_vec to i32)>
;
%s = select i1 ptrtoint (<2 x i32> ()* @all_constant_true_undef_false_constexpr_vec to i1), <2 x i32> undef, <2 x i32><i32 -1, i32 ptrtoint (<2 x i32> ()* @all_constant_true_undef_false_constexpr_vec to i32)>
ret <2 x i32> %s
Expand Down

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