[llvm] 21e3a21 - [InstCombine] Replace an integer comparison of a `phi` node with multiple `ucmp`/`scmp` operands and a constant with `phi` of individual comparisons of original intrinsic's arguments (#107769)
via llvm-commits
llvm-commits at lists.llvm.org
Fri Sep 13 11:50:31 PDT 2024
Author: Volodymyr Vasylkun
Date: 2024-09-13T19:50:27+01:00
New Revision: 21e3a212c570dc80055742ef8abbd0a306ff9135
URL: https://github.com/llvm/llvm-project/commit/21e3a212c570dc80055742ef8abbd0a306ff9135
DIFF: https://github.com/llvm/llvm-project/commit/21e3a212c570dc80055742ef8abbd0a306ff9135.diff
LOG: [InstCombine] Replace an integer comparison of a `phi` node with multiple `ucmp`/`scmp` operands and a constant with `phi` of individual comparisons of original intrinsic's arguments (#107769)
When we have a `phi` instruction with more than one of its incoming
values being a call to `ucmp` or `scmp`, which is then compared with an
integer constant, we can move the comparison through the `phi` into the
incoming basic blocks because we know that a comparison of `ucmp`/`scmp`
with a constant will be simplified by the next iteration of InstCombine.
There's a high chance that other similar patterns can be identified, in
which case they can be easily handled by the same code by moving the
check for "simplifiable" instructions into a lambda.
Added:
llvm/test/Transforms/InstCombine/phi-with-multiple-unsimplifiable-values.ll
Modified:
llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
Removed:
################################################################################
diff --git a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
index 2bdedfed47bdca..aa3f3fbdaeffa0 100644
--- a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
@@ -1809,8 +1809,8 @@ Instruction *InstCombinerImpl::foldOpIntoPhi(Instruction &I, PHINode *PN) {
// Check to see whether the instruction can be folded into each phi operand.
// If there is one operand that does not fold, remember the BB it is in.
SmallVector<Value *> NewPhiValues;
- BasicBlock *NonSimplifiedBB = nullptr;
- Value *NonSimplifiedInVal = nullptr;
+ SmallVector<unsigned int> OpsToMoveUseToIncomingBB;
+ bool SeenNonSimplifiedInVal = false;
for (unsigned i = 0; i != NumPHIValues; ++i) {
Value *InVal = PN->getIncomingValue(i);
BasicBlock *InBB = PN->getIncomingBlock(i);
@@ -1820,35 +1820,64 @@ Instruction *InstCombinerImpl::foldOpIntoPhi(Instruction &I, PHINode *PN) {
continue;
}
- if (NonSimplifiedBB) return nullptr; // More than one non-simplified value.
+ // If the only use of phi is comparing it with a constant then we can
+ // put this comparison in the incoming BB directly after a ucmp/scmp call
+ // because we know that it will simplify to a single icmp.
+ // NOTE: the single-use check here is not only to ensure that the
+ // optimization is profitable, but also to avoid creating a potentially
+ // invalid phi node when we have a multi-edge in the CFG.
+ const APInt *Ignored;
+ if (isa<CmpIntrinsic>(InVal) && InVal->hasOneUse() &&
+ match(&I, m_ICmp(m_Specific(PN), m_APInt(Ignored)))) {
+ OpsToMoveUseToIncomingBB.push_back(i);
+ NewPhiValues.push_back(nullptr);
+ continue;
+ }
+
+ if (SeenNonSimplifiedInVal)
+ return nullptr; // More than one non-simplified value.
+ SeenNonSimplifiedInVal = true;
+
+ // If there is exactly one non-simplified value, we can insert a copy of the
+ // operation in that block. However, if this is a critical edge, we would
+ // be inserting the computation on some other paths (e.g. inside a loop).
+ // Only do this if the pred block is unconditionally branching into the phi
+ // block. Also, make sure that the pred block is not dead code.
+ BranchInst *BI = dyn_cast<BranchInst>(InBB->getTerminator());
+ if (!BI || !BI->isUnconditional() || !DT.isReachableFromEntry(InBB))
+ return nullptr;
- NonSimplifiedBB = InBB;
- NonSimplifiedInVal = InVal;
NewPhiValues.push_back(nullptr);
+ OpsToMoveUseToIncomingBB.push_back(i);
// If the InVal is an invoke at the end of the pred block, then we can't
// insert a computation after it without breaking the edge.
if (isa<InvokeInst>(InVal))
- if (cast<Instruction>(InVal)->getParent() == NonSimplifiedBB)
+ if (cast<Instruction>(InVal)->getParent() == InBB)
return nullptr;
// Do not push the operation across a loop backedge. This could result in
// an infinite combine loop, and is generally non-profitable (especially
// if the operation was originally outside the loop).
- if (isBackEdge(NonSimplifiedBB, PN->getParent()))
+ if (isBackEdge(InBB, PN->getParent()))
return nullptr;
}
- // If there is exactly one non-simplified value, we can insert a copy of the
- // operation in that block. However, if this is a critical edge, we would be
- // inserting the computation on some other paths (e.g. inside a loop). Only
- // do this if the pred block is unconditionally branching into the phi block.
- // Also, make sure that the pred block is not dead code.
- if (NonSimplifiedBB != nullptr) {
- BranchInst *BI = dyn_cast<BranchInst>(NonSimplifiedBB->getTerminator());
- if (!BI || !BI->isUnconditional() ||
- !DT.isReachableFromEntry(NonSimplifiedBB))
- return nullptr;
+ // Clone the instruction that uses the phi node and move it into the incoming
+ // BB because we know that the next iteration of InstCombine will simplify it.
+ for (auto OpIndex : OpsToMoveUseToIncomingBB) {
+ Value *Op = PN->getIncomingValue(OpIndex);
+ BasicBlock *OpBB = PN->getIncomingBlock(OpIndex);
+
+ Instruction *Clone = I.clone();
+ for (Use &U : Clone->operands()) {
+ if (U == PN)
+ U = Op;
+ else
+ U = U->DoPHITranslation(PN->getParent(), OpBB);
+ }
+ Clone = InsertNewInstBefore(Clone, OpBB->getTerminator()->getIterator());
+ NewPhiValues[OpIndex] = Clone;
}
// Okay, we can do the transformation: create the new PHI node.
@@ -1857,30 +1886,13 @@ Instruction *InstCombinerImpl::foldOpIntoPhi(Instruction &I, PHINode *PN) {
NewPN->takeName(PN);
NewPN->setDebugLoc(PN->getDebugLoc());
- // If we are going to have to insert a new computation, do so right before the
- // predecessor's terminator.
- Instruction *Clone = nullptr;
- if (NonSimplifiedBB) {
- Clone = I.clone();
- for (Use &U : Clone->operands()) {
- if (U == PN)
- U = NonSimplifiedInVal;
- else
- U = U->DoPHITranslation(PN->getParent(), NonSimplifiedBB);
- }
- InsertNewInstBefore(Clone, NonSimplifiedBB->getTerminator()->getIterator());
- }
-
- for (unsigned i = 0; i != NumPHIValues; ++i) {
- if (NewPhiValues[i])
- NewPN->addIncoming(NewPhiValues[i], PN->getIncomingBlock(i));
- else
- NewPN->addIncoming(Clone, PN->getIncomingBlock(i));
- }
+ for (unsigned i = 0; i != NumPHIValues; ++i)
+ NewPN->addIncoming(NewPhiValues[i], PN->getIncomingBlock(i));
for (User *U : make_early_inc_range(PN->users())) {
Instruction *User = cast<Instruction>(U);
- if (User == &I) continue;
+ if (User == &I)
+ continue;
replaceInstUsesWith(*User, NewPN);
eraseInstFromFunction(*User);
}
diff --git a/llvm/test/Transforms/InstCombine/phi-with-multiple-unsimplifiable-values.ll b/llvm/test/Transforms/InstCombine/phi-with-multiple-unsimplifiable-values.ll
new file mode 100644
index 00000000000000..2b75d5c5475117
--- /dev/null
+++ b/llvm/test/Transforms/InstCombine/phi-with-multiple-unsimplifiable-values.ll
@@ -0,0 +1,135 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
+; RUN: opt < %s -passes=instcombine -S | FileCheck %s
+
+declare void @use(i8 %value);
+
+; Since we know that any comparison of ucmp/scmp with a constant will result in
+; a comparison of ucmp/scmp's operands, we can propagate such a comparison
+; through the phi node and let the next iteration of instcombine simplify it.
+define i1 @icmp_of_phi_of_scmp_with_constant(i1 %c, i16 %x, i16 %y)
+; CHECK-LABEL: define i1 @icmp_of_phi_of_scmp_with_constant(
+; CHECK-SAME: i1 [[C:%.*]], i16 [[X:%.*]], i16 [[Y:%.*]]) {
+; CHECK-NEXT: [[ENTRY:.*:]]
+; CHECK-NEXT: br i1 [[C]], label %[[TRUE:.*]], label %[[FALSE:.*]]
+; CHECK: [[TRUE]]:
+; CHECK-NEXT: [[TMP0:%.*]] = icmp slt i16 [[X]], [[Y]]
+; CHECK-NEXT: br label %[[EXIT:.*]]
+; CHECK: [[FALSE]]:
+; CHECK-NEXT: [[TMP1:%.*]] = icmp slt i16 [[Y]], [[X]]
+; CHECK-NEXT: br label %[[EXIT]]
+; CHECK: [[EXIT]]:
+; CHECK-NEXT: [[R:%.*]] = phi i1 [ [[TMP0]], %[[TRUE]] ], [ [[TMP1]], %[[FALSE]] ]
+; CHECK-NEXT: ret i1 [[R]]
+;
+{
+entry:
+ br i1 %c, label %true, label %false
+true:
+ %cmp1 = call i8 @llvm.scmp(i16 %x, i16 %y)
+ br label %exit
+false:
+ %cmp2 = call i8 @llvm.scmp(i16 %y, i16 %x)
+ br label %exit
+exit:
+ %phi = phi i8 [%cmp1, %true], [%cmp2, %false]
+ %r = icmp slt i8 %phi, 0
+ ret i1 %r
+}
+
+; When one of the incoming values is ucmp/scmp and the other is not we can still perform the transformation
+define i1 @icmp_of_phi_of_one_scmp_with_constant(i1 %c, i16 %x, i16 %y, i8 %false_val)
+; CHECK-LABEL: define i1 @icmp_of_phi_of_one_scmp_with_constant(
+; CHECK-SAME: i1 [[C:%.*]], i16 [[X:%.*]], i16 [[Y:%.*]], i8 [[FALSE_VAL:%.*]]) {
+; CHECK-NEXT: [[ENTRY:.*:]]
+; CHECK-NEXT: br i1 [[C]], label %[[TRUE:.*]], label %[[FALSE:.*]]
+; CHECK: [[TRUE]]:
+; CHECK-NEXT: [[TMP0:%.*]] = icmp slt i16 [[X]], [[Y]]
+; CHECK-NEXT: br label %[[EXIT:.*]]
+; CHECK: [[FALSE]]:
+; CHECK-NEXT: [[TMP1:%.*]] = icmp slt i8 [[FALSE_VAL]], 0
+; CHECK-NEXT: br label %[[EXIT]]
+; CHECK: [[EXIT]]:
+; CHECK-NEXT: [[PHI:%.*]] = phi i1 [ [[TMP0]], %[[TRUE]] ], [ [[TMP1]], %[[FALSE]] ]
+; CHECK-NEXT: ret i1 [[PHI]]
+;
+{
+entry:
+ br i1 %c, label %true, label %false
+true:
+ %cmp1 = call i8 @llvm.scmp(i16 %x, i16 %y)
+ br label %exit
+false:
+ br label %exit
+exit:
+ %phi = phi i8 [%cmp1, %true], [%false_val, %false]
+ %r = icmp slt i8 %phi, 0
+ ret i1 %r
+}
+
+; Negative test: the RHS of comparison that uses the phi node is not constant
+define i1 @icmp_of_phi_of_scmp_with_non_constant(i1 %c, i16 %x, i16 %y, i8 %cmp)
+; CHECK-LABEL: define i1 @icmp_of_phi_of_scmp_with_non_constant(
+; CHECK-SAME: i1 [[C:%.*]], i16 [[X:%.*]], i16 [[Y:%.*]], i8 [[CMP:%.*]]) {
+; CHECK-NEXT: [[ENTRY:.*:]]
+; CHECK-NEXT: br i1 [[C]], label %[[TRUE:.*]], label %[[FALSE:.*]]
+; CHECK: [[TRUE]]:
+; CHECK-NEXT: [[CMP1:%.*]] = call i8 @llvm.scmp.i8.i16(i16 [[X]], i16 [[Y]])
+; CHECK-NEXT: br label %[[EXIT:.*]]
+; CHECK: [[FALSE]]:
+; CHECK-NEXT: [[CMP2:%.*]] = call i8 @llvm.scmp.i8.i16(i16 [[Y]], i16 [[X]])
+; CHECK-NEXT: br label %[[EXIT]]
+; CHECK: [[EXIT]]:
+; CHECK-NEXT: [[PHI:%.*]] = phi i8 [ [[CMP1]], %[[TRUE]] ], [ [[CMP2]], %[[FALSE]] ]
+; CHECK-NEXT: [[R:%.*]] = icmp slt i8 [[PHI]], [[CMP]]
+; CHECK-NEXT: ret i1 [[R]]
+;
+{
+entry:
+ br i1 %c, label %true, label %false
+true:
+ %cmp1 = call i8 @llvm.scmp(i16 %x, i16 %y)
+ br label %exit
+false:
+ %cmp2 = call i8 @llvm.scmp(i16 %y, i16 %x)
+ br label %exit
+exit:
+ %phi = phi i8 [%cmp1, %true], [%cmp2, %false]
+ %r = icmp slt i8 %phi, %cmp
+ ret i1 %r
+}
+
+; Negative test: more than one incoming value of the phi node is not one-use
+define i1 @icmp_of_phi_of_scmp_with_constant_not_one_use(i1 %c, i16 %x, i16 %y)
+; CHECK-LABEL: define i1 @icmp_of_phi_of_scmp_with_constant_not_one_use(
+; CHECK-SAME: i1 [[C:%.*]], i16 [[X:%.*]], i16 [[Y:%.*]]) {
+; CHECK-NEXT: [[ENTRY:.*:]]
+; CHECK-NEXT: br i1 [[C]], label %[[TRUE:.*]], label %[[FALSE:.*]]
+; CHECK: [[TRUE]]:
+; CHECK-NEXT: [[CMP1:%.*]] = call i8 @llvm.scmp.i8.i16(i16 [[X]], i16 [[Y]])
+; CHECK-NEXT: call void @use(i8 [[CMP1]])
+; CHECK-NEXT: br label %[[EXIT:.*]]
+; CHECK: [[FALSE]]:
+; CHECK-NEXT: [[CMP2:%.*]] = call i8 @llvm.scmp.i8.i16(i16 [[Y]], i16 [[X]])
+; CHECK-NEXT: call void @use(i8 [[CMP2]])
+; CHECK-NEXT: br label %[[EXIT]]
+; CHECK: [[EXIT]]:
+; CHECK-NEXT: [[PHI:%.*]] = phi i8 [ [[CMP1]], %[[TRUE]] ], [ [[CMP2]], %[[FALSE]] ]
+; CHECK-NEXT: [[R:%.*]] = icmp slt i8 [[PHI]], 0
+; CHECK-NEXT: ret i1 [[R]]
+;
+{
+entry:
+ br i1 %c, label %true, label %false
+true:
+ %cmp1 = call i8 @llvm.scmp(i16 %x, i16 %y)
+ call void @use(i8 %cmp1)
+ br label %exit
+false:
+ %cmp2 = call i8 @llvm.scmp(i16 %y, i16 %x)
+ call void @use(i8 %cmp2)
+ br label %exit
+exit:
+ %phi = phi i8 [%cmp1, %true], [%cmp2, %false]
+ %r = icmp slt i8 %phi, 0
+ ret i1 %r
+}
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