[InstCombine] Try to freely invert phi nodes #80804
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@llvm/pr-subscribers-llvm-transforms Author: Yingwei Zheng (dtcxzyw) ChangesThis patch tries to invert phi nodes if all incoming values are either constants or nots. Full diff: https://github.com/llvm/llvm-project/pull/80804.diff 3 Files Affected:
diff --git a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
index dd168917f4dc9c..9a148636aebe35 100644
--- a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
@@ -2375,6 +2375,33 @@ Value *InstCombiner::getFreelyInvertedImpl(Value *V, bool WillInvertAllUses,
}
}
+ if (PHINode *PN = dyn_cast<PHINode>(V)) {
+ SmallVector<std::pair<Value *, BasicBlock *>, 8> IncomingValues;
+ for (Use &U : PN->operands()) {
+ BasicBlock *IncomingBlock = PN->getIncomingBlock(U);
+ if (isa<PHINode>(U.get()))
+ return nullptr;
+ Value *NewIncomingVal =
+ getFreelyInvertedImpl(U.get(), /*WillInvertAllUses=*/false,
+ /*Builder=*/nullptr, DoesConsume, Depth);
+ if (NewIncomingVal == nullptr)
+ return nullptr;
+ // Make sure that we can safely erase the original PHI node.
+ if (NewIncomingVal == V)
+ return nullptr;
+ if (Builder != nullptr)
+ IncomingValues.emplace_back(NewIncomingVal, IncomingBlock);
+ }
+ if (Builder != nullptr) {
+ PHINode *NewPN =
+ PHINode::Create(PN->getType(), PN->getNumIncomingValues(), "", PN);
+ for (auto [Val, Pred] : IncomingValues)
+ NewPN->addIncoming(Val, Pred);
+ return NewPN;
+ }
+ return NonNull;
+ }
+
return nullptr;
}
diff --git a/llvm/test/Transforms/InstCombine/div-i1.ll b/llvm/test/Transforms/InstCombine/div-i1.ll
index a14ef3588e611f..ad8aa71c8f1c88 100644
--- a/llvm/test/Transforms/InstCombine/div-i1.ll
+++ b/llvm/test/Transforms/InstCombine/div-i1.ll
@@ -1,5 +1,5 @@
; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
-; RUN: opt -S -passes=instcombine < %s | FileCheck %s
+; RUN: opt -S -passes='instcombine<no-verify-fixpoint>' < %s | FileCheck %s
define i1 @sdiv_by_zero_indirect_is_poison(i1 %c, i1 %x, i1 %y) {
; CHECK-LABEL: @sdiv_by_zero_indirect_is_poison(
@@ -132,6 +132,8 @@ define i1 @pt62607() {
; CHECK-NEXT: entry_1:
; CHECK-NEXT: br label [[LOOP_5:%.*]]
; CHECK: loop_5:
+; CHECK-NEXT: [[VAL_I1_55:%.*]] = phi i1 [ true, [[ENTRY_1:%.*]] ], [ poison, [[LOOP_5]] ]
+; CHECK-NEXT: call void @llvm.assume(i1 [[VAL_I1_55]])
; CHECK-NEXT: br i1 poison, label [[LOOP_5]], label [[LOOP_EXIT_8:%.*]]
; CHECK: loop_exit_8:
; CHECK-NEXT: ret i1 false
diff --git a/llvm/test/Transforms/InstCombine/free-inversion.ll b/llvm/test/Transforms/InstCombine/free-inversion.ll
index be9bedbf798598..a89887a586b582 100644
--- a/llvm/test/Transforms/InstCombine/free-inversion.ll
+++ b/llvm/test/Transforms/InstCombine/free-inversion.ll
@@ -9,6 +9,7 @@ declare i8 @llvm.umax.i8(i8, i8)
declare void @llvm.assume(i1)
declare void @use.i8(i8)
+declare void @use.i1(i1)
define i8 @xor_1(i8 %a, i1 %c, i8 %x, i8 %y) {
; CHECK-LABEL: @xor_1(
@@ -544,11 +545,198 @@ define i8 @lshr_not_nneg(i8 %x, i8 %y) {
define i8 @lshr_not_nneg2(i8 %x) {
; CHECK-LABEL: @lshr_not_nneg2(
; CHECK-NEXT: [[SHR:%.*]] = lshr i8 [[X:%.*]], 1
-; CHECK-NEXT: [[SHR_NOT1:%.*]] = or disjoint i8 [[SHR]], -128
-; CHECK-NEXT: ret i8 [[SHR_NOT1]]
+; CHECK-NEXT: [[SHR_NOT:%.*]] = or disjoint i8 [[SHR]], -128
+; CHECK-NEXT: ret i8 [[SHR_NOT]]
;
%x.not = xor i8 %x, -1
%shr = lshr i8 %x.not, 1
%shr.not = xor i8 %shr, -1
ret i8 %shr.not
}
+
+define i1 @test_inv_free(i1 %c1, i1 %c2, i1 %c3, i1 %c4) {
+; CHECK-LABEL: @test_inv_free(
+; CHECK-NEXT: entry:
+; CHECK-NEXT: br i1 [[C1:%.*]], label [[B1:%.*]], label [[B2:%.*]]
+; CHECK: b1:
+; CHECK-NEXT: br i1 [[C2:%.*]], label [[EXIT:%.*]], label [[B3:%.*]]
+; CHECK: b2:
+; CHECK-NEXT: br label [[EXIT]]
+; CHECK: b3:
+; CHECK-NEXT: br label [[EXIT]]
+; CHECK: exit:
+; CHECK-NEXT: [[VAL_NOT:%.*]] = phi i1 [ false, [[B1]] ], [ true, [[B2]] ], [ [[C3:%.*]], [[B3]] ]
+; CHECK-NEXT: [[COND_NOT:%.*]] = and i1 [[VAL_NOT]], [[C4:%.*]]
+; CHECK-NEXT: br i1 [[COND_NOT]], label [[B5:%.*]], label [[B4:%.*]]
+; CHECK: b4:
+; CHECK-NEXT: ret i1 true
+; CHECK: b5:
+; CHECK-NEXT: ret i1 false
+;
+entry:
+ br i1 %c1, label %b1, label %b2
+b1:
+ br i1 %c2, label %exit, label %b3
+b2:
+ br label %exit
+b3:
+ %invc3 = xor i1 %c3, true
+ br label %exit
+exit:
+ %val = phi i1 [ true, %b1 ], [ false, %b2 ], [ %invc3, %b3 ]
+ %inv = xor i1 %c4, true
+ %cond = or i1 %val, %inv
+ br i1 %cond, label %b4, label %b5
+b4:
+ ret i1 true
+b5:
+ ret i1 false
+}
+
+define i32 @test_inv_free_i32(i1 %c1, i1 %c2, i32 %c3, i32 %c4) {
+; CHECK-LABEL: @test_inv_free_i32(
+; CHECK-NEXT: entry:
+; CHECK-NEXT: br i1 [[C1:%.*]], label [[B1:%.*]], label [[B2:%.*]]
+; CHECK: b1:
+; CHECK-NEXT: br i1 [[C2:%.*]], label [[EXIT:%.*]], label [[B3:%.*]]
+; CHECK: b2:
+; CHECK-NEXT: br label [[EXIT]]
+; CHECK: b3:
+; CHECK-NEXT: br label [[EXIT]]
+; CHECK: exit:
+; CHECK-NEXT: [[TMP0:%.*]] = phi i32 [ 0, [[B1]] ], [ -1, [[B2]] ], [ [[C3:%.*]], [[B3]] ]
+; CHECK-NEXT: [[COND:%.*]] = xor i32 [[TMP0]], [[C4:%.*]]
+; CHECK-NEXT: ret i32 [[COND]]
+;
+entry:
+ br i1 %c1, label %b1, label %b2
+b1:
+ br i1 %c2, label %exit, label %b3
+b2:
+ br label %exit
+b3:
+ %invc3 = xor i32 %c3, -1
+ br label %exit
+exit:
+ %val = phi i32 [ -1, %b1 ], [ 0, %b2 ], [ %invc3, %b3 ]
+ %inv = xor i32 %c4, -1
+ %cond = xor i32 %val, %inv
+ ret i32 %cond
+}
+
+; Negative tests
+
+define i1 @test_inv_free_multiuse(i1 %c1, i1 %c2, i1 %c3, i1 %c4) {
+; CHECK-LABEL: @test_inv_free_multiuse(
+; CHECK-NEXT: entry:
+; CHECK-NEXT: br i1 [[C1:%.*]], label [[B1:%.*]], label [[B2:%.*]]
+; CHECK: b1:
+; CHECK-NEXT: br i1 [[C2:%.*]], label [[EXIT:%.*]], label [[B3:%.*]]
+; CHECK: b2:
+; CHECK-NEXT: br label [[EXIT]]
+; CHECK: b3:
+; CHECK-NEXT: [[INVC3:%.*]] = xor i1 [[C3:%.*]], true
+; CHECK-NEXT: br label [[EXIT]]
+; CHECK: exit:
+; CHECK-NEXT: [[VAL:%.*]] = phi i1 [ true, [[B1]] ], [ false, [[B2]] ], [ [[INVC3]], [[B3]] ]
+; CHECK-NEXT: call void @use.i1(i1 [[VAL]])
+; CHECK-NEXT: [[INV:%.*]] = xor i1 [[C4:%.*]], true
+; CHECK-NEXT: [[COND:%.*]] = or i1 [[VAL]], [[INV]]
+; CHECK-NEXT: br i1 [[COND]], label [[B4:%.*]], label [[B5:%.*]]
+; CHECK: b4:
+; CHECK-NEXT: ret i1 true
+; CHECK: b5:
+; CHECK-NEXT: ret i1 false
+;
+entry:
+ br i1 %c1, label %b1, label %b2
+b1:
+ br i1 %c2, label %exit, label %b3
+b2:
+ br label %exit
+b3:
+ %invc3 = xor i1 %c3, true
+ br label %exit
+exit:
+ %val = phi i1 [ true, %b1 ], [ false, %b2 ], [ %invc3, %b3 ]
+ call void @use.i1(i1 %val)
+ %inv = xor i1 %c4, true
+ %cond = or i1 %val, %inv
+ br i1 %cond, label %b4, label %b5
+b4:
+ ret i1 true
+b5:
+ ret i1 false
+}
+
+define i32 @test_inv_free_i32_newinst(i1 %c1, i1 %c2, i32 %c3, i32 %c4) {
+; CHECK-LABEL: @test_inv_free_i32_newinst(
+; CHECK-NEXT: entry:
+; CHECK-NEXT: br i1 [[C1:%.*]], label [[B1:%.*]], label [[B2:%.*]]
+; CHECK: b1:
+; CHECK-NEXT: br i1 [[C2:%.*]], label [[EXIT:%.*]], label [[B3:%.*]]
+; CHECK: b2:
+; CHECK-NEXT: br label [[EXIT]]
+; CHECK: b3:
+; CHECK-NEXT: [[ASHR:%.*]] = ashr i32 -8, [[C3:%.*]]
+; CHECK-NEXT: br label [[EXIT]]
+; CHECK: exit:
+; CHECK-NEXT: [[VAL:%.*]] = phi i32 [ -1, [[B1]] ], [ 0, [[B2]] ], [ [[ASHR]], [[B3]] ]
+; CHECK-NEXT: [[TMP0:%.*]] = xor i32 [[VAL]], [[C4:%.*]]
+; CHECK-NEXT: [[COND:%.*]] = xor i32 [[TMP0]], -1
+; CHECK-NEXT: ret i32 [[COND]]
+;
+entry:
+ br i1 %c1, label %b1, label %b2
+b1:
+ br i1 %c2, label %exit, label %b3
+b2:
+ br label %exit
+b3:
+ %ashr = ashr i32 -8, %c3
+ br label %exit
+exit:
+ %val = phi i32 [ -1, %b1 ], [ 0, %b2 ], [ %ashr, %b3 ]
+ %inv = xor i32 %c4, -1
+ %cond = xor i32 %val, %inv
+ ret i32 %cond
+}
+
+define i1 @test_inv_free_loop(i1 %c1, i1 %c2, i1 %c3, i1 %c4) {
+; CHECK-LABEL: @test_inv_free_loop(
+; CHECK-NEXT: entry:
+; CHECK-NEXT: br i1 [[C1:%.*]], label [[B1:%.*]], label [[B2:%.*]]
+; CHECK: b1:
+; CHECK-NEXT: br i1 [[C2:%.*]], label [[EXIT:%.*]], label [[B3:%.*]]
+; CHECK: b2:
+; CHECK-NEXT: br label [[EXIT]]
+; CHECK: b3:
+; CHECK-NEXT: [[INVC3:%.*]] = xor i1 [[C3:%.*]], true
+; CHECK-NEXT: br label [[EXIT]]
+; CHECK: exit:
+; CHECK-NEXT: [[VAL:%.*]] = phi i1 [ true, [[B1]] ], [ false, [[B2]] ], [ [[INVC3]], [[B3]] ], [ [[NOT:%.*]], [[EXIT]] ]
+; CHECK-NEXT: [[INV:%.*]] = xor i1 [[C4:%.*]], true
+; CHECK-NEXT: [[COND:%.*]] = or i1 [[VAL]], [[INV]]
+; CHECK-NEXT: [[NOT]] = xor i1 [[VAL]], true
+; CHECK-NEXT: br i1 [[COND]], label [[EXIT]], label [[B4:%.*]]
+; CHECK: b4:
+; CHECK-NEXT: ret i1 true
+;
+entry:
+ br i1 %c1, label %b1, label %b2
+b1:
+ br i1 %c2, label %exit, label %b3
+b2:
+ br label %exit
+b3:
+ %invc3 = xor i1 %c3, true
+ br label %exit
+exit:
+ %val = phi i1 [ true, %b1 ], [ false, %b2 ], [ %invc3, %b3 ], [ %not, %exit ]
+ %inv = xor i1 %c4, true
+ %cond = or i1 %val, %inv
+ %not = xor i1 %val, true
+ br i1 %cond, label %exit, label %b4
+b4:
+ ret i1 true
+}
|
nikic
reviewed
Feb 6, 2024
| return nullptr; | ||
| // Make sure that we can safely erase the original PHI node. | ||
| if (NewIncomingVal == V) | ||
| return nullptr; |
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Which test checks this case? I'm wondering if this is something that can happen indirectly.
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See the test @test_inv_free_loop. TBH I don't know why it happens. If the PHI node is used twice, WillInvertAllUses should be false.
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I think this is related to freelyInvertAllUsersOf() used for de-Morgan patterns. I think your check is fine.
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nikic
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Feb 7, 2024
| return nullptr; | ||
| // Make sure that we can safely erase the original PHI node. | ||
| if (NewIncomingVal == V) | ||
| return nullptr; |
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I think this is related to freelyInvertAllUsersOf() used for de-Morgan patterns. I think your check is fine.
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This patch tries to invert phi nodes if all incoming values are either constants or nots.