[llvm-branch-commits] [llvm] 0f8745b - Revert "[SimplifyCFG] When only one case value is missing, replace default with that case (#76669)"
Alexander Kornienko via llvm-branch-commits
llvm-branch-commits at lists.llvm.org
Wed Jan 17 08:51:35 PST 2024
Author: Alexander Kornienko
Date: 2024-01-17T17:49:25+01:00
New Revision: 0f8745b4b77d1c1fd0699adb024ed08bcb1233d3
URL: https://github.com/llvm/llvm-project/commit/0f8745b4b77d1c1fd0699adb024ed08bcb1233d3
DIFF: https://github.com/llvm/llvm-project/commit/0f8745b4b77d1c1fd0699adb024ed08bcb1233d3.diff
LOG: Revert "[SimplifyCFG] When only one case value is missing, replace default with that case (#76669)"
This reverts commit 7d81e072712f4e6a150561b5538ccebda289aa13, which introduces a
compiler memory usage regression. See
https://github.com/llvm/llvm-project/pull/76669#issuecomment-1887659952
Added:
Modified:
llvm/lib/Transforms/Utils/SimplifyCFG.cpp
llvm/test/Transforms/SimplifyCFG/switch-dead-default.ll
Removed:
llvm/test/Transforms/SimplifyCFG/switch-dead-default-lookup-table.ll
################################################################################
diff --git a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
index 7515e539e7fb78..f3994b6cc39fef 100644
--- a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -5414,13 +5414,11 @@ static bool CasesAreContiguous(SmallVectorImpl<ConstantInt *> &Cases) {
}
static void createUnreachableSwitchDefault(SwitchInst *Switch,
- DomTreeUpdater *DTU,
- bool RemoveOrigDefaultBlock = true) {
+ DomTreeUpdater *DTU) {
LLVM_DEBUG(dbgs() << "SimplifyCFG: switch default is dead.\n");
auto *BB = Switch->getParent();
auto *OrigDefaultBlock = Switch->getDefaultDest();
- if (RemoveOrigDefaultBlock)
- OrigDefaultBlock->removePredecessor(BB);
+ OrigDefaultBlock->removePredecessor(BB);
BasicBlock *NewDefaultBlock = BasicBlock::Create(
BB->getContext(), BB->getName() + ".unreachabledefault", BB->getParent(),
OrigDefaultBlock);
@@ -5429,8 +5427,7 @@ static void createUnreachableSwitchDefault(SwitchInst *Switch,
if (DTU) {
SmallVector<DominatorTree::UpdateType, 2> Updates;
Updates.push_back({DominatorTree::Insert, BB, &*NewDefaultBlock});
- if (RemoveOrigDefaultBlock &&
- !is_contained(successors(BB), OrigDefaultBlock))
+ if (!is_contained(successors(BB), OrigDefaultBlock))
Updates.push_back({DominatorTree::Delete, BB, &*OrigDefaultBlock});
DTU->applyUpdates(Updates);
}
@@ -5612,28 +5609,10 @@ static bool eliminateDeadSwitchCases(SwitchInst *SI, DomTreeUpdater *DTU,
Known.getBitWidth() - (Known.Zero | Known.One).popcount();
assert(NumUnknownBits <= Known.getBitWidth());
if (HasDefault && DeadCases.empty() &&
- NumUnknownBits < 64 /* avoid overflow */) {
- uint64_t AllNumCases = 1ULL << NumUnknownBits;
- if (SI->getNumCases() == AllNumCases) {
- createUnreachableSwitchDefault(SI, DTU);
- return true;
- }
- // When only one case value is missing, replace default with that case.
- // Eliminating the default branch will provide more opportunities for
- // optimization, such as lookup tables.
- if (SI->getNumCases() == AllNumCases - 1) {
- assert(NumUnknownBits > 1 && "Should be canonicalized to a branch");
- uint64_t MissingCaseVal = 0;
- for (const auto &Case : SI->cases())
- MissingCaseVal ^= Case.getCaseValue()->getValue().getLimitedValue();
- auto *MissingCase =
- cast<ConstantInt>(ConstantInt::get(Cond->getType(), MissingCaseVal));
- SwitchInstProfUpdateWrapper SIW(*SI);
- SIW.addCase(MissingCase, SI->getDefaultDest(), SIW.getSuccessorWeight(0));
- createUnreachableSwitchDefault(SI, DTU, /*RemoveOrigDefaultBlock*/ false);
- SIW.setSuccessorWeight(0, 0);
- return true;
- }
+ NumUnknownBits < 64 /* avoid overflow */ &&
+ SI->getNumCases() == (1ULL << NumUnknownBits)) {
+ createUnreachableSwitchDefault(SI, DTU);
+ return true;
}
if (DeadCases.empty())
diff --git a/llvm/test/Transforms/SimplifyCFG/switch-dead-default-lookup-table.ll b/llvm/test/Transforms/SimplifyCFG/switch-dead-default-lookup-table.ll
deleted file mode 100644
index bead0dc4c567a8..00000000000000
--- a/llvm/test/Transforms/SimplifyCFG/switch-dead-default-lookup-table.ll
+++ /dev/null
@@ -1,61 +0,0 @@
-; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 4
-; RUN: opt %s -S -passes='simplifycfg<switch-to-lookup>' -simplifycfg-require-and-preserve-domtree=1 -switch-range-to-icmp | FileCheck %s
-
-target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
-
-define i64 @test_1(i64 %0) {
-; CHECK-LABEL: define i64 @test_1(
-; CHECK-SAME: i64 [[TMP0:%.*]]) {
-; CHECK-NEXT: switch.lookup:
-; CHECK-NEXT: [[TMP1:%.*]] = urem i64 [[TMP0]], 4
-; CHECK-NEXT: [[SWITCH_GEP:%.*]] = getelementptr inbounds [4 x i64], ptr @switch.table.test_1, i32 0, i64 [[TMP1]]
-; CHECK-NEXT: [[SWITCH_LOAD:%.*]] = load i64, ptr [[SWITCH_GEP]], align 8
-; CHECK-NEXT: ret i64 [[SWITCH_LOAD]]
-;
- %2 = urem i64 %0, 4
- switch i64 %2, label %5 [
- i64 1, label %3
- i64 2, label %3
- i64 3, label %4
- ]
-
-3:
- br label %5
-
-4:
- br label %5
-
-5:
- %.0 = phi i64 [ 2, %4 ], [ 1, %3 ], [ 0, %1 ]
- ret i64 %.0
-}
-
-
-define i64 @test_2(i64 %0) {
-; CHECK-LABEL: define i64 @test_2(
-; CHECK-SAME: i64 [[TMP0:%.*]]) {
-; CHECK-NEXT: switch.lookup:
-; CHECK-NEXT: [[TMP1:%.*]] = urem i64 [[TMP0]], 4
-; CHECK-NEXT: ret i64 [[TMP1]]
-;
- %2 = urem i64 %0, 4
- switch i64 %2, label %6 [
- i64 1, label %3
- i64 2, label %4
- i64 3, label %5
- ]
-
-3:
- br label %6
-
-4:
- br label %6
-
-5:
- br label %6
-
-6:
- %.0 = phi i64 [ 0, %1 ], [ 1, %3 ], [ 2, %4 ], [ 3, %5 ]
- ret i64 %.0
-}
-
diff --git a/llvm/test/Transforms/SimplifyCFG/switch-dead-default.ll b/llvm/test/Transforms/SimplifyCFG/switch-dead-default.ll
index e30a535c523237..7c0d5e4f2b653c 100644
--- a/llvm/test/Transforms/SimplifyCFG/switch-dead-default.ll
+++ b/llvm/test/Transforms/SimplifyCFG/switch-dead-default.ll
@@ -79,15 +79,15 @@ default:
ret void
}
-; We can replace the default branch with case 3 since it is the only case that is missing.
+; This one is a negative test - we know the value of the default,
+; but that's about it
define void @test3(i2 %a) {
; CHECK-LABEL: define void @test3(
; CHECK-SAME: i2 [[A:%.*]]) {
-; CHECK-NEXT: switch i2 [[A]], label [[DOTUNREACHABLEDEFAULT:%.*]] [
+; CHECK-NEXT: switch i2 [[A]], label [[DEFAULT:%.*]] [
; CHECK-NEXT: i2 0, label [[CASE0:%.*]]
; CHECK-NEXT: i2 1, label [[CASE1:%.*]]
; CHECK-NEXT: i2 -2, label [[CASE2:%.*]]
-; CHECK-NEXT: i2 -1, label [[DEFAULT:%.*]]
; CHECK-NEXT: ]
; CHECK: common.ret:
; CHECK-NEXT: ret void
@@ -100,8 +100,6 @@ define void @test3(i2 %a) {
; CHECK: case2:
; CHECK-NEXT: call void @foo(i32 2)
; CHECK-NEXT: br label [[COMMON_RET]]
-; CHECK: .unreachabledefault:
-; CHECK-NEXT: unreachable
; CHECK: default:
; CHECK-NEXT: call void @foo(i32 3)
; CHECK-NEXT: br label [[COMMON_RET]]
@@ -124,50 +122,6 @@ default:
ret void
}
-define void @test3_prof(i2 %a) {
-; CHECK-LABEL: define void @test3_prof(
-; CHECK-SAME: i2 [[A:%.*]]) {
-; CHECK-NEXT: switch i2 [[A]], label [[DOTUNREACHABLEDEFAULT:%.*]] [
-; CHECK-NEXT: i2 0, label [[CASE0:%.*]]
-; CHECK-NEXT: i2 1, label [[CASE1:%.*]]
-; CHECK-NEXT: i2 -2, label [[CASE2:%.*]]
-; CHECK-NEXT: i2 -1, label [[DEFAULT:%.*]]
-; CHECK-NEXT: ], !prof [[PROF0:![0-9]+]]
-; CHECK: common.ret:
-; CHECK-NEXT: ret void
-; CHECK: case0:
-; CHECK-NEXT: call void @foo(i32 0)
-; CHECK-NEXT: br label [[COMMON_RET:%.*]]
-; CHECK: case1:
-; CHECK-NEXT: call void @foo(i32 1)
-; CHECK-NEXT: br label [[COMMON_RET]]
-; CHECK: case2:
-; CHECK-NEXT: call void @foo(i32 2)
-; CHECK-NEXT: br label [[COMMON_RET]]
-; CHECK: .unreachabledefault:
-; CHECK-NEXT: unreachable
-; CHECK: default:
-; CHECK-NEXT: call void @foo(i32 3)
-; CHECK-NEXT: br label [[COMMON_RET]]
-;
- switch i2 %a, label %default [i2 0, label %case0
- i2 1, label %case1
- i2 2, label %case2], !prof !0
-
-case0:
- call void @foo(i32 0)
- ret void
-case1:
- call void @foo(i32 1)
- ret void
-case2:
- call void @foo(i32 2)
- ret void
-default:
- call void @foo(i32 3)
- ret void
-}
-
; Negative test - check for possible overflow when computing
; number of possible cases.
define void @test4(i128 %a) {
@@ -313,7 +267,3 @@ default:
declare void @llvm.assume(i1)
-!0 = !{!"branch_weights", i32 8, i32 4, i32 2, i32 1}
-;.
-; CHECK: [[PROF0]] = !{!"branch_weights", i32 0, i32 4, i32 2, i32 1, i32 8}
-;.
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