[llvm] [SimplifyCFG] Simplify conditional branches on const icmp eq's (PR #73334)
via llvm-commits
llvm-commits at lists.llvm.org
Sat Nov 25 03:35:47 PST 2023
https://github.com/yonillasky updated https://github.com/llvm/llvm-project/pull/73334
>From 73edb086254e9453df35defa5f0c83edb5a8d335 Mon Sep 17 00:00:00 2001
From: Yoni Lavi <yoni.lavi at nextsilicon.com>
Date: Fri, 24 Nov 2023 16:25:19 +0200
Subject: [PATCH] [SimplifyCFG] Simplify conditional branches on const icmp
eq's
---
llvm/include/llvm/Transforms/Utils/Local.h | 3 +-
.../lib/Transforms/Scalar/SimplifyCFGPass.cpp | 45 +++++++++++++++-
llvm/lib/Transforms/Utils/Local.cpp | 5 +-
.../test/Analysis/MemorySSA/nondeterminism.ll | 2 +-
.../Transforms/Coroutines/coro-alloca-01.ll | 2 +-
.../Transforms/Coroutines/coro-alloca-07.ll | 6 +--
.../Coroutines/coro-alloca-outside-frame.ll | 2 +-
.../coro-spill-defs-before-corobegin.ll | 4 +-
...ntersection-block-with-dead-predecessor.ll | 52 +++++++++++++++++++
9 files changed, 106 insertions(+), 15 deletions(-)
create mode 100644 llvm/test/Transforms/SimplifyCFG/intersection-block-with-dead-predecessor.ll
diff --git a/llvm/include/llvm/Transforms/Utils/Local.h b/llvm/include/llvm/Transforms/Utils/Local.h
index 2df3c9049c7d62e..86b86e8196fad36 100644
--- a/llvm/include/llvm/Transforms/Utils/Local.h
+++ b/llvm/include/llvm/Transforms/Utils/Local.h
@@ -392,7 +392,8 @@ Instruction *removeUnwindEdge(BasicBlock *BB, DomTreeUpdater *DTU = nullptr);
///
/// Returns true if any basic block was removed.
bool removeUnreachableBlocks(Function &F, DomTreeUpdater *DTU = nullptr,
- MemorySSAUpdater *MSSAU = nullptr);
+ MemorySSAUpdater *MSSAU = nullptr,
+ bool KeepOneInputPHIs = false);
/// Combine the metadata of two instructions so that K can replace J. Some
/// metadata kinds can only be kept if K does not move, meaning it dominated
diff --git a/llvm/lib/Transforms/Scalar/SimplifyCFGPass.cpp b/llvm/lib/Transforms/Scalar/SimplifyCFGPass.cpp
index 7017f6adf3a2bbe..f40d4d863ac6dcb 100644
--- a/llvm/lib/Transforms/Scalar/SimplifyCFGPass.cpp
+++ b/llvm/lib/Transforms/Scalar/SimplifyCFGPass.cpp
@@ -26,6 +26,7 @@
#include "llvm/ADT/Statistic.h"
#include "llvm/Analysis/AssumptionCache.h"
#include "llvm/Analysis/CFG.h"
+#include "llvm/Analysis/ConstantFolding.h"
#include "llvm/Analysis/DomTreeUpdater.h"
#include "llvm/Analysis/GlobalsModRef.h"
#include "llvm/Analysis/TargetTransformInfo.h"
@@ -262,12 +263,52 @@ static bool iterativelySimplifyCFG(Function &F, const TargetTransformInfo &TTI,
return Changed;
}
+static void decayOneInputPHIs(BasicBlock &BB) {
+ if (BB.empty() || !isa<PHINode>(BB.begin()))
+ return;
+ unsigned NumPreds = cast<PHINode>(BB.front()).getNumIncomingValues();
+ if (NumPreds != 1)
+ return;
+ for (PHINode &Phi : make_early_inc_range(BB.phis())) {
+ if (Value *PhiConst = Phi.hasConstantValue()) {
+ Phi.replaceAllUsesWith(PhiConst);
+ Phi.eraseFromParent();
+ // Additionally, constant-fold conditional branch if there is one present,
+ // and the PHI has decayed into a constant, since it may make another CFG
+ // edge dead.
+ if (!isa<Constant>(PhiConst))
+ continue;
+ if (BranchInst *BI = dyn_cast<BranchInst>(BB.getTerminator()))
+ if (BI->isConditional())
+ if (auto *Cmp = dyn_cast<CmpInst>(BI->getCondition()))
+ if (auto *LHS = dyn_cast<Constant>(Cmp->getOperand(0)))
+ if (auto *RHS = dyn_cast<Constant>(Cmp->getOperand(1))) {
+ const DataLayout &DL = BB.getModule()->getDataLayout();
+ Constant *ConstCond = ConstantFoldCompareInstOperands(
+ Cmp->getPredicate(), LHS, RHS, DL);
+ if (ConstCond)
+ BI->setCondition(ConstCond);
+ }
+ }
+ }
+}
+
+static bool removeUnreachableBlocksAndSimplify(Function &F,
+ DomTreeUpdater *DTU) {
+ bool Changed = removeUnreachableBlocks(F, DTU, /*MSSAU=*/nullptr,
+ /*KeepOneInputPHIs=*/true);
+ if (Changed)
+ for (BasicBlock &BB : F)
+ decayOneInputPHIs(BB);
+ return Changed;
+}
+
static bool simplifyFunctionCFGImpl(Function &F, const TargetTransformInfo &TTI,
DominatorTree *DT,
const SimplifyCFGOptions &Options) {
DomTreeUpdater DTU(DT, DomTreeUpdater::UpdateStrategy::Eager);
- bool EverChanged = removeUnreachableBlocks(F, DT ? &DTU : nullptr);
+ bool EverChanged = removeUnreachableBlocksAndSimplify(F, DT ? &DTU : nullptr);
EverChanged |=
tailMergeBlocksWithSimilarFunctionTerminators(F, DT ? &DTU : nullptr);
EverChanged |= iterativelySimplifyCFG(F, TTI, DT ? &DTU : nullptr, Options);
@@ -285,7 +326,7 @@ static bool simplifyFunctionCFGImpl(Function &F, const TargetTransformInfo &TTI,
do {
EverChanged = iterativelySimplifyCFG(F, TTI, DT ? &DTU : nullptr, Options);
- EverChanged |= removeUnreachableBlocks(F, DT ? &DTU : nullptr);
+ EverChanged |= removeUnreachableBlocksAndSimplify(F, DT ? &DTU : nullptr);
} while (EverChanged);
return true;
diff --git a/llvm/lib/Transforms/Utils/Local.cpp b/llvm/lib/Transforms/Utils/Local.cpp
index 8c6c112ebacff2d..35b76b1511d51f5 100644
--- a/llvm/lib/Transforms/Utils/Local.cpp
+++ b/llvm/lib/Transforms/Utils/Local.cpp
@@ -3080,7 +3080,8 @@ Instruction *llvm::removeUnwindEdge(BasicBlock *BB, DomTreeUpdater *DTU) {
/// if they are in a dead cycle. Return true if a change was made, false
/// otherwise.
bool llvm::removeUnreachableBlocks(Function &F, DomTreeUpdater *DTU,
- MemorySSAUpdater *MSSAU) {
+ MemorySSAUpdater *MSSAU,
+ bool KeepOneInputPHIs) {
SmallPtrSet<BasicBlock *, 16> Reachable;
bool Changed = markAliveBlocks(F, Reachable, DTU);
@@ -3111,7 +3112,7 @@ bool llvm::removeUnreachableBlocks(Function &F, DomTreeUpdater *DTU,
if (MSSAU)
MSSAU->removeBlocks(BlocksToRemove);
- DeleteDeadBlocks(BlocksToRemove.takeVector(), DTU);
+ DeleteDeadBlocks(BlocksToRemove.takeVector(), DTU, KeepOneInputPHIs);
return Changed;
}
diff --git a/llvm/test/Analysis/MemorySSA/nondeterminism.ll b/llvm/test/Analysis/MemorySSA/nondeterminism.ll
index 90902e36b5d58ab..312cd6e4709a906 100644
--- a/llvm/test/Analysis/MemorySSA/nondeterminism.ll
+++ b/llvm/test/Analysis/MemorySSA/nondeterminism.ll
@@ -1,7 +1,7 @@
; RUN: opt -passes=simplifycfg -S --preserve-ll-uselistorder %s | FileCheck %s
; REQUIRES: x86-registered-target
; CHECK-LABEL: @n
-; CHECK: uselistorder i16 0, { 3, 2, 4, 1, 5, 0, 6 }
+; CHECK: uselistorder i16 0, { 0, 1, 4, 3, 5, 2, 6 }
; Note: test was added in an effort to ensure determinism when updating memoryssa. See PR42574.
; If the uselistorder check becomes no longer relevant, the test can be disabled or removed.
diff --git a/llvm/test/Transforms/Coroutines/coro-alloca-01.ll b/llvm/test/Transforms/Coroutines/coro-alloca-01.ll
index 5208c055c4fdf2c..88b1883e651c5cf 100644
--- a/llvm/test/Transforms/Coroutines/coro-alloca-01.ll
+++ b/llvm/test/Transforms/Coroutines/coro-alloca-01.ll
@@ -42,7 +42,7 @@ suspend:
; CHECK-LABEL: @f(
; CHECK: %x.reload.addr = getelementptr inbounds %f.Frame, ptr %hdl, i32 0, i32 2
; CHECK: %y.reload.addr = getelementptr inbounds %f.Frame, ptr %hdl, i32 0, i32 3
-; CHECK: %alias_phi = phi ptr [ %y.reload.addr, %merge.from.flag_false ], [ %x.reload.addr, %entry ]
+; CHECK: %alias_phi = select i1 %n, ptr %x.reload.addr, ptr %y.reload.addr
; CHECK: %alias_phi.spill.addr = getelementptr inbounds %f.Frame, ptr %hdl, i32 0, i32 4
; CHECK: store ptr %alias_phi, ptr %alias_phi.spill.addr, align 8
diff --git a/llvm/test/Transforms/Coroutines/coro-alloca-07.ll b/llvm/test/Transforms/Coroutines/coro-alloca-07.ll
index c81bf333f2059d5..0967303b3a48994 100644
--- a/llvm/test/Transforms/Coroutines/coro-alloca-07.ll
+++ b/llvm/test/Transforms/Coroutines/coro-alloca-07.ll
@@ -70,11 +70,7 @@ declare void @free(ptr)
; CHECK-NEXT: store ptr @f.destroy, ptr [[DESTROY_ADDR]], align 8
; CHECK-NEXT: [[X_RELOAD_ADDR:%.*]] = getelementptr inbounds [[F_FRAME]], ptr [[HDL]], i32 0, i32 2
; CHECK-NEXT: [[Y_RELOAD_ADDR:%.*]] = getelementptr inbounds [[F_FRAME]], ptr [[HDL]], i32 0, i32 3
-; CHECK-NEXT: br i1 [[N:%.*]], label [[MERGE:%.*]], label [[MERGE_FROM_FLAG_FALSE:%.*]]
-; CHECK: merge.from.flag_false:
-; CHECK-NEXT: br label [[MERGE:%.*]]
-; CHECK: merge:
-; CHECK-NEXT: [[ALIAS_PHI:%.*]] = phi ptr [ [[Y_RELOAD_ADDR]], [[MERGE_FROM_FLAG_FALSE]] ], [ [[X_RELOAD_ADDR]], [[ENTRY:%.*]] ]
+; CHECK-NEXT: [[ALIAS_PHI:%.*]] = select i1 [[N:%.*]], ptr [[X_RELOAD_ADDR]], ptr [[Y_RELOAD_ADDR]]
; CHECK-NEXT: [[ALIAS_PHI_SPILL_ADDR:%.*]] = getelementptr inbounds [[F_FRAME]], ptr [[HDL]], i32 0, i32 4
; CHECK-NEXT: store ptr [[ALIAS_PHI]], ptr [[ALIAS_PHI_SPILL_ADDR]], align 8
; CHECK-NEXT: store i8 1, ptr [[ALIAS_PHI]], align 1
diff --git a/llvm/test/Transforms/Coroutines/coro-alloca-outside-frame.ll b/llvm/test/Transforms/Coroutines/coro-alloca-outside-frame.ll
index ac6a5752438cedb..0318822778901f4 100644
--- a/llvm/test/Transforms/Coroutines/coro-alloca-outside-frame.ll
+++ b/llvm/test/Transforms/Coroutines/coro-alloca-outside-frame.ll
@@ -43,7 +43,7 @@ suspend:
; CHECK: %x = alloca i64, align 8, !coro.outside.frame !0
; CHECK-NOT: %x.reload.addr = getelementptr inbounds %f.Frame, ptr %hdl, i32 0, i32 2
; CHECK: %y.reload.addr = getelementptr inbounds %f.Frame, ptr %hdl, i32 0, i32 2
-; CHECK: %alias_phi = phi ptr [ %y.reload.addr, %merge.from.flag_false ], [ %x, %entry ]
+; CHECK: %alias_phi = select i1 %n, ptr %x, ptr %y.reload.addr
declare ptr @llvm.coro.free(token, ptr)
declare i32 @llvm.coro.size.i32()
diff --git a/llvm/test/Transforms/Coroutines/coro-spill-defs-before-corobegin.ll b/llvm/test/Transforms/Coroutines/coro-spill-defs-before-corobegin.ll
index 801c4a177613532..39eb39ccf02d633 100644
--- a/llvm/test/Transforms/Coroutines/coro-spill-defs-before-corobegin.ll
+++ b/llvm/test/Transforms/Coroutines/coro-spill-defs-before-corobegin.ll
@@ -51,7 +51,7 @@ lpad:
; CHECK-LABEL: @f(
; CHECK: %alloc = call ptr @malloc(i32 32)
; CHECK-NEXT: %flag = call i1 @check(ptr %alloc)
-; CHECK-NEXT: %spec.select = select i1 %flag, i32 0, i32 1
+; CHECK-NEXT: %value_phi = select i1 %flag, i32 0, i32 1
; CHECK-NEXT: %value_invoke = call i32 @calc()
; CHECK-NEXT: %hdl = call noalias nonnull ptr @llvm.coro.begin(token %id, ptr %alloc)
@@ -59,7 +59,7 @@ lpad:
; CHECK-NEXT: %value_invoke.spill.addr = getelementptr inbounds %f.Frame, ptr %hdl, i32 0, i32 3
; CHECK-NEXT: store i32 %value_invoke, ptr %value_invoke.spill.addr
; CHECK-NEXT: %value_phi.spill.addr = getelementptr inbounds %f.Frame, ptr %hdl, i32 0, i32 2
-; CHECK-NEXT: store i32 %spec.select, ptr %value_phi.spill.addr
+; CHECK-NEXT: store i32 %value_phi, ptr %value_phi.spill.addr
declare ptr @llvm.coro.free(token, ptr)
declare i32 @llvm.coro.size.i32()
diff --git a/llvm/test/Transforms/SimplifyCFG/intersection-block-with-dead-predecessor.ll b/llvm/test/Transforms/SimplifyCFG/intersection-block-with-dead-predecessor.ll
new file mode 100644
index 000000000000000..d60a8e0dfaf4755
--- /dev/null
+++ b/llvm/test/Transforms/SimplifyCFG/intersection-block-with-dead-predecessor.ll
@@ -0,0 +1,52 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 4
+; RUN: opt < %s -passes=simplifycfg -simplifycfg-require-and-preserve-domtree=1 -S | FileCheck %s
+
+; A pre-existing foldable pattern should remain intact
+define void @const_valued_cond_br(ptr %P) {
+; CHECK-LABEL: define void @const_valued_cond_br(
+; CHECK-SAME: ptr [[P:%.*]]) {
+; CHECK-NEXT: entry:
+; CHECK-NEXT: [[COND:%.*]] = icmp eq i32 42, 42
+; CHECK-NEXT: br i1 [[COND]], label [[A:%.*]], label [[B:%.*]]
+; CHECK: a:
+; CHECK-NEXT: store i32 123, ptr [[P]], align 4
+; CHECK-NEXT: br label [[B]]
+; CHECK: b:
+; CHECK-NEXT: ret void
+;
+entry:
+ %cond = icmp eq i32 42, 42
+ br i1 %cond, label %a, label %b
+a:
+ store i32 123, ptr %P
+ br label %b
+b:
+ ret void
+}
+
+; When the phi decays to a constant, the terminator of `b` gets constant-folded,
+; enabling further simplification.
+define void @intersection_block_with_dead_predecessor(ptr %P) {
+; CHECK-LABEL: define void @intersection_block_with_dead_predecessor(
+; CHECK-SAME: ptr [[P:%.*]]) {
+; CHECK-NEXT: entry:
+; CHECK-NEXT: [[COND:%.*]] = icmp eq i32 1, 1
+; CHECK-NEXT: store i32 321, ptr [[P]], align 4
+; CHECK-NEXT: ret void
+;
+entry:
+ br label %b
+b:
+ %x = phi i32 [1, %entry], [2, %a]
+ switch i32 %x, label %c [
+ i32 1, label %d
+ ]
+c:
+ store i32 123, ptr %P
+ ret void
+d:
+ store i32 321, ptr %P
+ ret void
+a: ; unreachable
+ br label %b
+}
More information about the llvm-commits
mailing list