[InstCombine] Don't folder select to or if value argument is user of invalid addrspacecast inst #144686
Conversation
…invalid addrspacecast inst In our downstream GPU target, following IR is valid before instcombine although the second addrspacecast causes UB. define i1 @test(ptr addrspace(1) noundef %v) { %0 = addrspacecast ptr addrspace(1) %v to ptr addrspace(4) %1 = call i32 @llvm.xxxx.isaddr.shared(ptr addrspace(4) %0) %2 = icmp eq i32 %1, 0 %3 = addrspacecast ptr addrspace(4) %0 to ptr addrspace(3) %4 = select i1 %2, ptr addrspace(3) null, ptr addrspace(3) %3 %5 = icmp eq ptr addrspace(3) %4, null ret i1 %5 } We have a custom optimization that replaces invalid addrspacecast with poison, and IR is still valid since `select` stops poison propagation. However, instcombine pass optimizes `select` to `or`: %0 = addrspacecast ptr addrspace(1) %v to ptr addrspace(4) %1 = call i32 @llvm.xxxx.isaddr.shared(ptr addrspace(4) %0) %2 = icmp eq i32 %1, 0 %3 = addrspacecast ptr addrspace(1) %v to ptr addrspace(3) %4 = icmp eq ptr addrspace(3) %3, null %5 = or i1 %2, %4 ret i1 %5 The transform is invalid for our target.
|
@llvm/pr-subscribers-llvm-ir @llvm/pr-subscribers-backend-amdgpu Author: Wenju He (wenju-he) ChangesIn our downstream GPU target, following IR is valid before instcombine although the second addrspacecast causes UB. However, instcombine pass optimizes Full diff: https://github.com/llvm/llvm-project/pull/144686.diff 2 Files Affected:
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp b/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
index 73ba0f78e8053..a2335640f917b 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
@@ -3194,8 +3194,23 @@ static Instruction *foldNestedSelects(SelectInst &OuterSelVal,
/// Return true if V is poison or \p Expected given that ValAssumedPoison is
/// already poison. For example, if ValAssumedPoison is `icmp samesign X, 10`
/// and V is `icmp ne X, 5`, impliesPoisonOrCond returns true.
-static bool impliesPoisonOrCond(const Value *ValAssumedPoison, const Value *V,
- bool Expected) {
+static bool impliesPoisonOrCond(
+ const Value *ValAssumedPoison, const Value *V, bool Expected,
+ llvm::function_ref<bool(unsigned, unsigned)> isValidAddrSpaceCast) {
+ // Handle the case that ValAssumedPoison is `icmp eq ptr addrspace(3) X, null`
+ // and X is `addrspacecast ptr addrspace(1) Y to ptr addrspace(3)`. Target can
+ // replace X with poison if the addrspacecast is invalid. However, `V` might
+ // not be poison.
+ if (auto *ICmp = dyn_cast<ICmpInst>(ValAssumedPoison)) {
+ auto CanCreatePoison = [&](Value *Op) {
+ auto *ASC = dyn_cast<AddrSpaceCastInst>(Op);
+ return ASC && !isValidAddrSpaceCast(ASC->getDestAddressSpace(),
+ ASC->getSrcAddressSpace());
+ };
+ if (llvm::any_of(ICmp->operands(), CanCreatePoison))
+ return false;
+ }
+
if (impliesPoison(ValAssumedPoison, V))
return true;
@@ -3241,17 +3256,23 @@ Instruction *InstCombinerImpl::foldSelectOfBools(SelectInst &SI) {
auto *Zero = ConstantInt::getFalse(SelType);
Value *A, *B, *C, *D;
+ auto IsValidAddrSpaceCast = [&](unsigned FromAS, unsigned ToAS) {
+ return isValidAddrSpaceCast(FromAS, ToAS);
+ };
+
// Folding select to and/or i1 isn't poison safe in general. impliesPoison
// checks whether folding it does not convert a well-defined value into
// poison.
if (match(TrueVal, m_One())) {
- if (impliesPoisonOrCond(FalseVal, CondVal, /*Expected=*/false)) {
+ if (impliesPoisonOrCond(FalseVal, CondVal, /*Expected=*/false,
+ IsValidAddrSpaceCast)) {
// Change: A = select B, true, C --> A = or B, C
return BinaryOperator::CreateOr(CondVal, FalseVal);
}
if (match(CondVal, m_OneUse(m_Select(m_Value(A), m_One(), m_Value(B)))) &&
- impliesPoisonOrCond(FalseVal, B, /*Expected=*/false)) {
+ impliesPoisonOrCond(FalseVal, B, /*Expected=*/false,
+ IsValidAddrSpaceCast)) {
// (A || B) || C --> A || (B | C)
return replaceInstUsesWith(
SI, Builder.CreateLogicalOr(A, Builder.CreateOr(B, FalseVal)));
@@ -3287,13 +3308,15 @@ Instruction *InstCombinerImpl::foldSelectOfBools(SelectInst &SI) {
}
if (match(FalseVal, m_Zero())) {
- if (impliesPoisonOrCond(TrueVal, CondVal, /*Expected=*/true)) {
+ if (impliesPoisonOrCond(TrueVal, CondVal, /*Expected=*/true,
+ IsValidAddrSpaceCast)) {
// Change: A = select B, C, false --> A = and B, C
return BinaryOperator::CreateAnd(CondVal, TrueVal);
}
if (match(CondVal, m_OneUse(m_Select(m_Value(A), m_Value(B), m_Zero()))) &&
- impliesPoisonOrCond(TrueVal, B, /*Expected=*/true)) {
+ impliesPoisonOrCond(TrueVal, B, /*Expected=*/true,
+ IsValidAddrSpaceCast)) {
// (A && B) && C --> A && (B & C)
return replaceInstUsesWith(
SI, Builder.CreateLogicalAnd(A, Builder.CreateAnd(B, TrueVal)));
diff --git a/llvm/test/Transforms/InstCombine/AMDGPU/addrspacecast.ll b/llvm/test/Transforms/InstCombine/AMDGPU/addrspacecast.ll
new file mode 100644
index 0000000000000..4791d2c434884
--- /dev/null
+++ b/llvm/test/Transforms/InstCombine/AMDGPU/addrspacecast.ll
@@ -0,0 +1,23 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
+; RUN: opt -S -mtriple=amdgcn-amd-amdhsa -passes=instcombine %s | FileCheck %s
+
+; Check that `select B, true, C` isn't optimized to `or B, C`.
+define i1 @not_fold_select(ptr addrspace(1) noundef %x) {
+; CHECK-LABEL: define i1 @not_fold_select(
+; CHECK-SAME: ptr addrspace(1) noundef [[X:%.*]]) {
+; CHECK-NEXT: [[ENTRY:.*:]]
+; CHECK-NEXT: [[TMP0:%.*]] = addrspacecast ptr addrspace(1) [[X]] to ptr
+; CHECK-NEXT: [[TMP1:%.*]] = tail call i1 @llvm.amdgcn.is.shared(ptr [[TMP0]])
+; CHECK-NEXT: [[TMP2:%.*]] = addrspacecast ptr addrspace(1) [[X]] to ptr addrspace(3)
+; CHECK-NEXT: [[TMP3:%.*]] = icmp eq ptr addrspace(3) [[TMP2]], null
+; CHECK-NEXT: [[TMP4:%.*]] = select i1 [[TMP1]], i1 true, i1 [[TMP3]]
+; CHECK-NEXT: ret i1 [[TMP4]]
+;
+ entry:
+ %0 = addrspacecast ptr addrspace(1) %x to ptr
+ %1 = tail call i1 @llvm.amdgcn.is.shared(ptr %0)
+ %2 = addrspacecast ptr %0 to ptr addrspace(3)
+ %3 = select i1 %1, ptr addrspace(3) null, ptr addrspace(3) %2
+ %4 = icmp eq ptr addrspace(3) %3, null
+ ret i1 %4
+}
|
|
@llvm/pr-subscribers-llvm-transforms Author: Wenju He (wenju-he) ChangesIn our downstream GPU target, following IR is valid before instcombine although the second addrspacecast causes UB. However, instcombine pass optimizes Full diff: https://github.com/llvm/llvm-project/pull/144686.diff 2 Files Affected:
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp b/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
index 73ba0f78e8053..a2335640f917b 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
@@ -3194,8 +3194,23 @@ static Instruction *foldNestedSelects(SelectInst &OuterSelVal,
/// Return true if V is poison or \p Expected given that ValAssumedPoison is
/// already poison. For example, if ValAssumedPoison is `icmp samesign X, 10`
/// and V is `icmp ne X, 5`, impliesPoisonOrCond returns true.
-static bool impliesPoisonOrCond(const Value *ValAssumedPoison, const Value *V,
- bool Expected) {
+static bool impliesPoisonOrCond(
+ const Value *ValAssumedPoison, const Value *V, bool Expected,
+ llvm::function_ref<bool(unsigned, unsigned)> isValidAddrSpaceCast) {
+ // Handle the case that ValAssumedPoison is `icmp eq ptr addrspace(3) X, null`
+ // and X is `addrspacecast ptr addrspace(1) Y to ptr addrspace(3)`. Target can
+ // replace X with poison if the addrspacecast is invalid. However, `V` might
+ // not be poison.
+ if (auto *ICmp = dyn_cast<ICmpInst>(ValAssumedPoison)) {
+ auto CanCreatePoison = [&](Value *Op) {
+ auto *ASC = dyn_cast<AddrSpaceCastInst>(Op);
+ return ASC && !isValidAddrSpaceCast(ASC->getDestAddressSpace(),
+ ASC->getSrcAddressSpace());
+ };
+ if (llvm::any_of(ICmp->operands(), CanCreatePoison))
+ return false;
+ }
+
if (impliesPoison(ValAssumedPoison, V))
return true;
@@ -3241,17 +3256,23 @@ Instruction *InstCombinerImpl::foldSelectOfBools(SelectInst &SI) {
auto *Zero = ConstantInt::getFalse(SelType);
Value *A, *B, *C, *D;
+ auto IsValidAddrSpaceCast = [&](unsigned FromAS, unsigned ToAS) {
+ return isValidAddrSpaceCast(FromAS, ToAS);
+ };
+
// Folding select to and/or i1 isn't poison safe in general. impliesPoison
// checks whether folding it does not convert a well-defined value into
// poison.
if (match(TrueVal, m_One())) {
- if (impliesPoisonOrCond(FalseVal, CondVal, /*Expected=*/false)) {
+ if (impliesPoisonOrCond(FalseVal, CondVal, /*Expected=*/false,
+ IsValidAddrSpaceCast)) {
// Change: A = select B, true, C --> A = or B, C
return BinaryOperator::CreateOr(CondVal, FalseVal);
}
if (match(CondVal, m_OneUse(m_Select(m_Value(A), m_One(), m_Value(B)))) &&
- impliesPoisonOrCond(FalseVal, B, /*Expected=*/false)) {
+ impliesPoisonOrCond(FalseVal, B, /*Expected=*/false,
+ IsValidAddrSpaceCast)) {
// (A || B) || C --> A || (B | C)
return replaceInstUsesWith(
SI, Builder.CreateLogicalOr(A, Builder.CreateOr(B, FalseVal)));
@@ -3287,13 +3308,15 @@ Instruction *InstCombinerImpl::foldSelectOfBools(SelectInst &SI) {
}
if (match(FalseVal, m_Zero())) {
- if (impliesPoisonOrCond(TrueVal, CondVal, /*Expected=*/true)) {
+ if (impliesPoisonOrCond(TrueVal, CondVal, /*Expected=*/true,
+ IsValidAddrSpaceCast)) {
// Change: A = select B, C, false --> A = and B, C
return BinaryOperator::CreateAnd(CondVal, TrueVal);
}
if (match(CondVal, m_OneUse(m_Select(m_Value(A), m_Value(B), m_Zero()))) &&
- impliesPoisonOrCond(TrueVal, B, /*Expected=*/true)) {
+ impliesPoisonOrCond(TrueVal, B, /*Expected=*/true,
+ IsValidAddrSpaceCast)) {
// (A && B) && C --> A && (B & C)
return replaceInstUsesWith(
SI, Builder.CreateLogicalAnd(A, Builder.CreateAnd(B, TrueVal)));
diff --git a/llvm/test/Transforms/InstCombine/AMDGPU/addrspacecast.ll b/llvm/test/Transforms/InstCombine/AMDGPU/addrspacecast.ll
new file mode 100644
index 0000000000000..4791d2c434884
--- /dev/null
+++ b/llvm/test/Transforms/InstCombine/AMDGPU/addrspacecast.ll
@@ -0,0 +1,23 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
+; RUN: opt -S -mtriple=amdgcn-amd-amdhsa -passes=instcombine %s | FileCheck %s
+
+; Check that `select B, true, C` isn't optimized to `or B, C`.
+define i1 @not_fold_select(ptr addrspace(1) noundef %x) {
+; CHECK-LABEL: define i1 @not_fold_select(
+; CHECK-SAME: ptr addrspace(1) noundef [[X:%.*]]) {
+; CHECK-NEXT: [[ENTRY:.*:]]
+; CHECK-NEXT: [[TMP0:%.*]] = addrspacecast ptr addrspace(1) [[X]] to ptr
+; CHECK-NEXT: [[TMP1:%.*]] = tail call i1 @llvm.amdgcn.is.shared(ptr [[TMP0]])
+; CHECK-NEXT: [[TMP2:%.*]] = addrspacecast ptr addrspace(1) [[X]] to ptr addrspace(3)
+; CHECK-NEXT: [[TMP3:%.*]] = icmp eq ptr addrspace(3) [[TMP2]], null
+; CHECK-NEXT: [[TMP4:%.*]] = select i1 [[TMP1]], i1 true, i1 [[TMP3]]
+; CHECK-NEXT: ret i1 [[TMP4]]
+;
+ entry:
+ %0 = addrspacecast ptr addrspace(1) %x to ptr
+ %1 = tail call i1 @llvm.amdgcn.is.shared(ptr %0)
+ %2 = addrspacecast ptr %0 to ptr addrspace(3)
+ %3 = select i1 %1, ptr addrspace(3) null, ptr addrspace(3) %2
+ %4 = icmp eq ptr addrspace(3) %3, null
+ ret i1 %4
+}
|
There was a problem hiding this comment.
If an invalid addrspacecast can produce poison, then this must be specified in
llvm-project/llvm/lib/Analysis/ValueTracking.cpp
Line 7352 in 34a4894
|
addrspacecast can produce poison. That's how we're handling the cases of addrspacecasts that are unimplementable |
| ; CHECK-NEXT: ret i1 [[TMP4]] | ||
| ; | ||
| entry: | ||
| %0 = addrspacecast ptr addrspace(1) %x to ptr |
| bool Expected) { | ||
| static bool impliesPoisonOrCond( | ||
| const Value *ValAssumedPoison, const Value *V, bool Expected, | ||
| llvm::function_ref<bool(unsigned, unsigned)> isValidAddrSpaceCast) { |
This PR uses isValidAddrSpaceCast query from TTI which is available in InstCombine. But TTI isn't available in above canCreateUndefOrPoison function.
done in ffff2c3, please review |
I don't think special handling of addrspacecast in |
| @@ -12621,6 +12621,9 @@ have no side effects, and must not capture the value of the pointer. | |||
| If the source is :ref:`poison <poisonvalues>`, the result is | |||
| :ref:`poison <poisonvalues>`. | |||
|
|
|||
| If the source is not :ref:`poison <poisonvalues>`, and the result pointer is | |||
| non-dereferenceable, the result is :ref:`poison <poisonvalues>`. | |||
There was a problem hiding this comment.
This is incorrect, not every addrspacecast of a non-dereferenceable pointer should automatically result in poison (e.g. the pointer to the end of an object is non-dereferenceable, but should certainly not turn into poison).
This should instead say something along the lines of:
Which address space casts are supported depends on the target. Unsupported address space casts return a poison value.
In our downstream GPU target, following IR is valid before instcombine although the second addrspacecast causes UB.
define i1 @test(ptr addrspace(1) noundef %v) {
%0 = addrspacecast ptr addrspace(1) %v to ptr addrspace(4)
%1 = call i32 @llvm.xxxx.isaddr.shared(ptr addrspace(4) %0)
%2 = icmp eq i32 %1, 0
%3 = addrspacecast ptr addrspace(4) %0 to ptr addrspace(3)
%4 = select i1 %2, ptr addrspace(3) null, ptr addrspace(3) %3
%5 = icmp eq ptr addrspace(3) %4, null
ret i1 %5
}
We have a custom optimization that replaces invalid addrspacecast with poison, and IR is still valid since
selectstops poison propagation.However, instcombine pass optimizes
selecttoor:%0 = addrspacecast ptr addrspace(1) %v to ptr addrspace(4)
%1 = call i32 @llvm.xxxx.isaddr.shared(ptr addrspace(4) %0)
%2 = icmp eq i32 %1, 0
%3 = addrspacecast ptr addrspace(1) %v to ptr addrspace(3)
%4 = icmp eq ptr addrspace(3) %3, null
%5 = or i1 %2, %4
ret i1 %5
The transform is invalid for our target.