[llvm] 20f0c68 - [SimplifyCFG] Allow dropping block that only contains ephemeral values
Nikita Popov via llvm-commits
llvm-commits at lists.llvm.org
Fri Jun 30 06:24:10 PDT 2023
Author: Nikita Popov
Date: 2023-06-30T15:24:01+02:00
New Revision: 20f0c68fd83a0147a8ec1722bd2e848180610288
URL: https://github.com/llvm/llvm-project/commit/20f0c68fd83a0147a8ec1722bd2e848180610288
DIFF: https://github.com/llvm/llvm-project/commit/20f0c68fd83a0147a8ec1722bd2e848180610288.diff
LOG: [SimplifyCFG] Allow dropping block that only contains ephemeral values
Perform the TryToSimplifyUncondBranchFromEmptyBlock() transform if
the block is empty except for ephemeral values. The ephemeral values
will be dropped in that case.
This makes sure that assumes don't block this transforms, as reported
in https://discourse.llvm.org/t/llvm-assume-blocks-optimization/71609.
Differential Revision: https://reviews.llvm.org/D153966
Added:
Modified:
llvm/include/llvm/Transforms/Utils/Local.h
llvm/lib/Transforms/Utils/Local.cpp
llvm/lib/Transforms/Utils/SimplifyCFG.cpp
llvm/test/CodeGen/Thumb2/pr52817.ll
llvm/test/Transforms/LoopVectorize/ARM/pointer_iv.ll
llvm/test/Transforms/SimplifyCFG/X86/critedge-assume.ll
llvm/test/Transforms/SimplifyCFG/assume.ll
llvm/test/Transforms/SimplifyCFG/gepcost.ll
llvm/test/Transforms/SimplifyCFG/hoist-common-skip.ll
Removed:
################################################################################
diff --git a/llvm/include/llvm/Transforms/Utils/Local.h b/llvm/include/llvm/Transforms/Utils/Local.h
index 4578af069814d0..b2f11cbb84f677 100644
--- a/llvm/include/llvm/Transforms/Utils/Local.h
+++ b/llvm/include/llvm/Transforms/Utils/Local.h
@@ -156,8 +156,11 @@ void MergeBasicBlockIntoOnlyPred(BasicBlock *BB, DomTreeUpdater *DTU = nullptr);
/// other than PHI nodes, potential debug intrinsics and the branch. If
/// possible, eliminate BB by rewriting all the predecessors to branch to the
/// successor block and return true. If we can't transform, return false.
-bool TryToSimplifyUncondBranchFromEmptyBlock(BasicBlock *BB,
- DomTreeUpdater *DTU = nullptr);
+/// If a RemoveInsts set is specified, the block may additionally contain these
+/// instructions, which will be removed as part of the transform.
+bool TryToSimplifyUncondBranchFromEmptyBlock(
+ BasicBlock *BB, DomTreeUpdater *DTU = nullptr,
+ const SmallPtrSetImpl<const Instruction *> *RemoveInsts = nullptr);
/// Check for and eliminate duplicate PHI nodes in this block. This doesn't try
/// to be clever about PHI nodes which
diff er only in the order of the incoming
diff --git a/llvm/lib/Transforms/Utils/Local.cpp b/llvm/lib/Transforms/Utils/Local.cpp
index f153ace5d3fc53..8618d1e87d7fdd 100644
--- a/llvm/lib/Transforms/Utils/Local.cpp
+++ b/llvm/lib/Transforms/Utils/Local.cpp
@@ -1059,8 +1059,9 @@ static void redirectValuesFromPredecessorsToPhi(BasicBlock *BB,
replaceUndefValuesInPhi(PN, IncomingValues);
}
-bool llvm::TryToSimplifyUncondBranchFromEmptyBlock(BasicBlock *BB,
- DomTreeUpdater *DTU) {
+bool llvm::TryToSimplifyUncondBranchFromEmptyBlock(
+ BasicBlock *BB, DomTreeUpdater *DTU,
+ const SmallPtrSetImpl<const Instruction *> *RemoveInsts) {
assert(BB != &BB->getParent()->getEntryBlock() &&
"TryToSimplifyUncondBranchFromEmptyBlock called on entry block!");
@@ -1173,6 +1174,15 @@ bool llvm::TryToSimplifyUncondBranchFromEmptyBlock(BasicBlock *BB,
LLVM_DEBUG(dbgs() << "Killing Trivial BB: \n" << *BB);
+ if (RemoveInsts) {
+ for (Instruction &I : make_early_inc_range(*BB)) {
+ if (RemoveInsts->contains(&I)) {
+ I.replaceAllUsesWith(PoisonValue::get(I.getType()));
+ I.eraseFromParent();
+ }
+ }
+ }
+
SmallVector<DominatorTree::UpdateType, 32> Updates;
if (DTU) {
// To avoid processing the same predecessor more than once.
diff --git a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
index 5d3bc44e93c5e6..149eb46e966fac 100644
--- a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -2660,7 +2660,13 @@ class EphemeralValueTracker {
return false;
}
+ bool empty() const { return EphValues.empty(); }
+
bool contains(const Instruction *I) const { return EphValues.contains(I); }
+
+ const SmallPtrSetImpl<const Instruction *> &getEphemeralValues() const {
+ return EphValues;
+ }
};
} // namespace
@@ -6929,6 +6935,22 @@ bool SimplifyCFGOpt::simplifyBranch(BranchInst *Branch, IRBuilder<> &Builder) {
: simplifyCondBranch(Branch, Builder);
}
+static bool isMostlyEmptyBlock(EphemeralValueTracker &EphTracker,
+ BasicBlock *BB) {
+ for (Instruction &I : reverse(drop_end(BB->instructionsWithoutDebug()))) {
+ // Block can contain phi nodes for this transform.
+ if (isa<PHINode>(I))
+ return true;
+ // Removing EH pads requires additional transforms, even if unused.
+ if (I.isEHPad())
+ return false;
+ if (EphTracker.track(&I))
+ continue;
+ return false;
+ }
+ return true;
+}
+
bool SimplifyCFGOpt::simplifyUncondBranch(BranchInst *BI,
IRBuilder<> &Builder) {
BasicBlock *BB = BI->getParent();
@@ -6945,13 +6967,21 @@ bool SimplifyCFGOpt::simplifyUncondBranch(BranchInst *BI,
Options.NeedCanonicalLoop &&
(!LoopHeaders.empty() && BB->hasNPredecessorsOrMore(2) &&
(is_contained(LoopHeaders, BB) || is_contained(LoopHeaders, Succ)));
- BasicBlock::iterator I = BB->getFirstNonPHIOrDbg(true)->getIterator();
- if (I->isTerminator() && BB != &BB->getParent()->getEntryBlock() &&
- !NeedCanonicalLoop && TryToSimplifyUncondBranchFromEmptyBlock(BB, DTU))
- return true;
+ if (!BB->isEntryBlock() && !NeedCanonicalLoop) {
+ EphemeralValueTracker EphTracker;
+ // If there are ephemeral values and we have a single predecessor, let
+ // MergeBlockIntoPredecessor() handle it, as it does not need to drop the
+ // ephemeral values.
+ if (isMostlyEmptyBlock(EphTracker, BB) &&
+ (EphTracker.empty() || !Succ->getSinglePredecessor()) &&
+ TryToSimplifyUncondBranchFromEmptyBlock(
+ BB, DTU, &EphTracker.getEphemeralValues()))
+ return true;
+ }
// If the only instruction in the block is a seteq/setne comparison against a
// constant, try to simplify the block.
+ BasicBlock::iterator I = BB->getFirstNonPHIOrDbg(true)->getIterator();
if (ICmpInst *ICI = dyn_cast<ICmpInst>(I))
if (ICI->isEquality() && isa<ConstantInt>(ICI->getOperand(1))) {
for (++I; isa<DbgInfoIntrinsic>(I); ++I)
diff --git a/llvm/test/CodeGen/Thumb2/pr52817.ll b/llvm/test/CodeGen/Thumb2/pr52817.ll
index 87615f0a1f7ef4..4afe15d49b5b68 100644
--- a/llvm/test/CodeGen/Thumb2/pr52817.ll
+++ b/llvm/test/CodeGen/Thumb2/pr52817.ll
@@ -1,5 +1,5 @@
; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
-; RUN: llc -mtriple=thumbv7-apple-ios9.0.0 -verify-machineinstrs < %s | FileCheck %s
+; RUN: llc -mtriple=thumbv7-apple-ios9.0.0 -arm-atomic-cfg-tidy=0 -verify-machineinstrs < %s | FileCheck %s
; Make sure machine verification does not fail due to incorrect bundle kill
; flags.
diff --git a/llvm/test/Transforms/LoopVectorize/ARM/pointer_iv.ll b/llvm/test/Transforms/LoopVectorize/ARM/pointer_iv.ll
index 12fb1fa821cd45..6ce3830b344396 100644
--- a/llvm/test/Transforms/LoopVectorize/ARM/pointer_iv.ll
+++ b/llvm/test/Transforms/LoopVectorize/ARM/pointer_iv.ll
@@ -62,8 +62,8 @@ define hidden void @pointer_phi_v4i32_add2(ptr noalias nocapture readonly %A, pt
; CHECK-NEXT: [[TMP2:%.*]] = add nsw <4 x i32> [[STRIDED_VEC]], [[BROADCAST_SPLAT]]
; CHECK-NEXT: store <4 x i32> [[TMP2]], ptr [[NEXT_GEP4]], align 4
; CHECK-NEXT: [[INDEX_NEXT]] = add nuw i32 [[INDEX]], 4
-; CHECK-NEXT: [[TMP4:%.*]] = icmp eq i32 [[INDEX_NEXT]], 996
-; CHECK-NEXT: br i1 [[TMP4]], label [[FOR_BODY:%.*]], label [[VECTOR_BODY]], !llvm.loop [[LOOP3:![0-9]+]]
+; CHECK-NEXT: [[TMP3:%.*]] = icmp eq i32 [[INDEX_NEXT]], 996
+; CHECK-NEXT: br i1 [[TMP3]], label [[FOR_BODY:%.*]], label [[VECTOR_BODY]], !llvm.loop [[LOOP3:![0-9]+]]
; CHECK: for.body:
; CHECK-NEXT: [[A_ADDR_09:%.*]] = phi ptr [ [[ADD_PTR:%.*]], [[FOR_BODY]] ], [ [[IND_END]], [[VECTOR_BODY]] ]
; CHECK-NEXT: [[I_08:%.*]] = phi i32 [ [[INC:%.*]], [[FOR_BODY]] ], [ 996, [[VECTOR_BODY]] ]
@@ -881,20 +881,16 @@ for.body:
define hidden void @mult_ptr_iv(ptr noalias nocapture readonly %x, ptr noalias nocapture %z) {
; CHECK-LABEL: @mult_ptr_iv(
; CHECK-NEXT: entry:
-; CHECK-NEXT: [[UGLYGEP:%.*]] = getelementptr i8, ptr [[Z:%.*]], i32 3000
-; CHECK-NEXT: [[UGLYGEP1:%.*]] = getelementptr i8, ptr [[X:%.*]], i32 3000
-; CHECK-NEXT: [[BOUND0:%.*]] = icmp ugt ptr [[UGLYGEP1]], [[Z]]
-; CHECK-NEXT: [[BOUND1:%.*]] = icmp ugt ptr [[UGLYGEP]], [[X]]
+; CHECK-NEXT: [[SCEVGEP:%.*]] = getelementptr i8, ptr [[Z:%.*]], i32 3000
+; CHECK-NEXT: [[SCEVGEP1:%.*]] = getelementptr i8, ptr [[X:%.*]], i32 3000
+; CHECK-NEXT: [[BOUND0:%.*]] = icmp ugt ptr [[SCEVGEP1]], [[Z]]
+; CHECK-NEXT: [[BOUND1:%.*]] = icmp ugt ptr [[SCEVGEP]], [[X]]
; CHECK-NEXT: [[FOUND_CONFLICT:%.*]] = and i1 [[BOUND0]], [[BOUND1]]
-; CHECK-NEXT: br i1 [[FOUND_CONFLICT]], label [[FOR_BODY:%.*]], label [[VECTOR_PH:%.*]]
-; CHECK: vector.ph:
-; CHECK-NEXT: [[IND_END:%.*]] = getelementptr i8, ptr [[X]], i32 3000
-; CHECK-NEXT: [[IND_END2:%.*]] = getelementptr i8, ptr [[Z]], i32 3000
-; CHECK-NEXT: br label [[VECTOR_BODY:%.*]]
+; CHECK-NEXT: br i1 [[FOUND_CONFLICT]], label [[FOR_BODY:%.*]], label [[VECTOR_BODY:%.*]]
; CHECK: vector.body:
-; CHECK-NEXT: [[POINTER_PHI:%.*]] = phi ptr [ [[X]], [[VECTOR_PH]] ], [ [[PTR_IND:%.*]], [[VECTOR_BODY]] ]
-; CHECK-NEXT: [[POINTER_PHI5:%.*]] = phi ptr [ [[Z]], [[VECTOR_PH]] ], [ [[PTR_IND6:%.*]], [[VECTOR_BODY]] ]
-; CHECK-NEXT: [[INDEX:%.*]] = phi i32 [ 0, [[VECTOR_PH]] ], [ [[INDEX_NEXT:%.*]], [[VECTOR_BODY]] ]
+; CHECK-NEXT: [[POINTER_PHI:%.*]] = phi ptr [ [[PTR_IND:%.*]], [[VECTOR_BODY]] ], [ [[X]], [[ENTRY:%.*]] ]
+; CHECK-NEXT: [[POINTER_PHI5:%.*]] = phi ptr [ [[PTR_IND6:%.*]], [[VECTOR_BODY]] ], [ [[Z]], [[ENTRY]] ]
+; CHECK-NEXT: [[INDEX:%.*]] = phi i32 [ [[INDEX_NEXT:%.*]], [[VECTOR_BODY]] ], [ 0, [[ENTRY]] ]
; CHECK-NEXT: [[TMP0:%.*]] = getelementptr i8, ptr [[POINTER_PHI]], <4 x i32> <i32 0, i32 3, i32 6, i32 9>
; CHECK-NEXT: [[TMP1:%.*]] = getelementptr i8, ptr [[POINTER_PHI5]], <4 x i32> <i32 0, i32 3, i32 6, i32 9>
; CHECK-NEXT: [[TMP2:%.*]] = getelementptr inbounds i8, <4 x ptr> [[TMP0]], i32 1
@@ -916,7 +912,7 @@ define hidden void @mult_ptr_iv(ptr noalias nocapture readonly %x, ptr noalias n
; CHECK-NEXT: [[TMP9:%.*]] = icmp eq i32 [[INDEX_NEXT]], 1000
; CHECK-NEXT: br i1 [[TMP9]], label [[END:%.*]], label [[VECTOR_BODY]], !llvm.loop [[LOOP33:![0-9]+]]
; CHECK: for.body:
-; CHECK-NEXT: [[X_ADDR_050:%.*]] = phi ptr [ [[INCDEC_PTR2:%.*]], [[FOR_BODY]] ], [ [[X]], [[ENTRY:%.*]] ]
+; CHECK-NEXT: [[X_ADDR_050:%.*]] = phi ptr [ [[INCDEC_PTR2:%.*]], [[FOR_BODY]] ], [ [[X]], [[ENTRY]] ]
; CHECK-NEXT: [[Z_ADDR_049:%.*]] = phi ptr [ [[INCDEC_PTR34:%.*]], [[FOR_BODY]] ], [ [[Z]], [[ENTRY]] ]
; CHECK-NEXT: [[I_048:%.*]] = phi i32 [ [[INC:%.*]], [[FOR_BODY]] ], [ 0, [[ENTRY]] ]
; CHECK-NEXT: [[INCDEC_PTR:%.*]] = getelementptr inbounds i8, ptr [[X_ADDR_050]], i32 1
diff --git a/llvm/test/Transforms/SimplifyCFG/X86/critedge-assume.ll b/llvm/test/Transforms/SimplifyCFG/X86/critedge-assume.ll
index 58ca8df8ff6d6e..b561f093e314d3 100644
--- a/llvm/test/Transforms/SimplifyCFG/X86/critedge-assume.ll
+++ b/llvm/test/Transforms/SimplifyCFG/X86/critedge-assume.ll
@@ -45,7 +45,6 @@ _ZN10unique_ptrD2Ev.exit:
%vtable.i.i = load ptr, ptr %call8, align 8
%x3 = tail call i1 @llvm.type.test(ptr %vtable.i.i, metadata !"foo")
; CHECK: call void @llvm.assume
- ; CHECK: call void @llvm.assume
tail call void @llvm.assume(i1 %x3) #5
br i1 %cmp, label %while.end.loopexit, label %while.body
diff --git a/llvm/test/Transforms/SimplifyCFG/assume.ll b/llvm/test/Transforms/SimplifyCFG/assume.ll
index eaebf376a9d72f..c85eee8c1b9c43 100644
--- a/llvm/test/Transforms/SimplifyCFG/assume.ll
+++ b/llvm/test/Transforms/SimplifyCFG/assume.ll
@@ -133,11 +133,7 @@ join:
define void @empty_block_with_assume(i1 %c, i32 %x) {
; CHECK-LABEL: @empty_block_with_assume(
; CHECK-NEXT: entry:
-; CHECK-NEXT: br i1 [[C:%.*]], label [[IF:%.*]], label [[ELSE:%.*]]
-; CHECK: if:
-; CHECK-NEXT: [[CMP:%.*]] = icmp ne i32 [[X:%.*]], 0
-; CHECK-NEXT: call void @llvm.assume(i1 [[CMP]])
-; CHECK-NEXT: br label [[JOIN:%.*]]
+; CHECK-NEXT: br i1 [[C:%.*]], label [[JOIN:%.*]], label [[ELSE:%.*]]
; CHECK: else:
; CHECK-NEXT: call void @dummy()
; CHECK-NEXT: br label [[JOIN]]
diff --git a/llvm/test/Transforms/SimplifyCFG/gepcost.ll b/llvm/test/Transforms/SimplifyCFG/gepcost.ll
index a4497ae71881e7..8cb23a461df71a 100644
--- a/llvm/test/Transforms/SimplifyCFG/gepcost.ll
+++ b/llvm/test/Transforms/SimplifyCFG/gepcost.ll
@@ -9,11 +9,6 @@ target triple = "thumbv7m-none--eabi"
define void @f(i1 %c) {
; CHECK-LABEL: @f(
; CHECK-NEXT: entr:
-; CHECK-NEXT: br i1 %c, label [[NEXT:%.*]], label [[EXIT:%.*]]
-; CHECK: next:
-; CHECK-NEXT: [[PAT:%.*]] = getelementptr [16 x i8], ptr @glob
-; CHECK-NEXT: br label [[EXIT]]
-; CHECK: exit:
; CHECK-NEXT: ret void
;
entr:
diff --git a/llvm/test/Transforms/SimplifyCFG/hoist-common-skip.ll b/llvm/test/Transforms/SimplifyCFG/hoist-common-skip.ll
index 5b6eeda7c7847e..76455c30359d97 100644
--- a/llvm/test/Transforms/SimplifyCFG/hoist-common-skip.ll
+++ b/llvm/test/Transforms/SimplifyCFG/hoist-common-skip.ll
@@ -107,14 +107,6 @@ define void @f3(i1 %c, ptr nocapture noundef %d, ptr nocapture noundef readonly
; CHECK-NEXT: [[ADD_0:%.*]] = add nsw i16 [[TMP0]], 1
; CHECK-NEXT: [[TMP1:%.*]] = load i16, ptr [[M:%.*]], align 2
; CHECK-NEXT: [[U:%.*]] = add i16 [[ADD_0]], [[TMP1]]
-; CHECK-NEXT: br i1 [[C:%.*]], label [[IF_THEN:%.*]], label [[IF_ELSE:%.*]]
-; CHECK: if.then:
-; CHECK-NEXT: call void @no_side_effects0()
-; CHECK-NEXT: br label [[IF_END:%.*]]
-; CHECK: if.else:
-; CHECK-NEXT: call void @no_side_effects1()
-; CHECK-NEXT: br label [[IF_END]]
-; CHECK: if.end:
; CHECK-NEXT: store i16 [[U]], ptr [[D:%.*]], align 2
; CHECK-NEXT: ret void
;
@@ -237,14 +229,6 @@ define void @f6(i1 %c, ptr nocapture noundef %d, ptr nocapture noundef readonly
; CHECK-NEXT: [[TMP0:%.*]] = load i16, ptr [[B:%.*]], align 2
; CHECK-NEXT: [[DIV_0:%.*]] = sdiv i16 211, [[TMP0]]
; CHECK-NEXT: [[U:%.*]] = add i16 [[DIV_0]], [[TMP0]]
-; CHECK-NEXT: br i1 [[C:%.*]], label [[IF_THEN:%.*]], label [[IF_ELSE:%.*]]
-; CHECK: if.then:
-; CHECK-NEXT: call void @no_side_effects0()
-; CHECK-NEXT: br label [[IF_END:%.*]]
-; CHECK: if.else:
-; CHECK-NEXT: call void @no_side_effects1()
-; CHECK-NEXT: br label [[IF_END]]
-; CHECK: if.end:
; CHECK-NEXT: store i16 [[U]], ptr [[D:%.*]], align 2
; CHECK-NEXT: ret void
;
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