[llvm] [SimplifyCFG] Fold switch over ucmp/scmp to icmp and br (PR #105636)
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Thu Aug 22 03:09:37 PDT 2024
llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-llvm-transforms
Author: Nikita Popov (nikic)
<details>
<summary>Changes</summary>
If we switch over ucmp/scmp and have two switch cases going to the same destination, we can convert into icmp+br.
Fixes https://github.com/llvm/llvm-project/issues/105632.
---
Full diff: https://github.com/llvm/llvm-project/pull/105636.diff
2 Files Affected:
- (modified) llvm/lib/Transforms/Utils/SimplifyCFG.cpp (+56)
- (modified) llvm/test/Transforms/SimplifyCFG/switch-on-cmp.ll (+19-46)
``````````diff
diff --git a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
index 00efd3c0eb72ec..d7295d89078b6c 100644
--- a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -7131,6 +7131,59 @@ static bool simplifySwitchOfPowersOfTwo(SwitchInst *SI, IRBuilder<> &Builder,
return true;
}
+/// Fold switch over ucmp/scmp intrinsic to br if two of the switch arms have
+/// the same destination.
+static bool simplifySwitchOfCmpIntrinsic(SwitchInst *SI,
+ IRBuilderBase &Builder) {
+ auto *Cmp = dyn_cast<CmpIntrinsic>(SI->getCondition());
+ if (!Cmp || !Cmp->hasOneUse() || SI->getNumCases() != 2)
+ return false;
+
+ // Find which of 1, 0 or -1 is missing.
+ SmallSet<int64_t, 3> Missing;
+ Missing.insert(1);
+ Missing.insert(0);
+ Missing.insert(-1);
+ BasicBlock *Succ = nullptr;
+ for (auto &Case : SI->cases()) {
+ std::optional<int64_t> Val = Case.getCaseValue()->getValue().trySExtValue();
+ if (!Val)
+ return false;
+ if (!Missing.erase(*Val))
+ return false;
+ if (Succ && Succ != Case.getCaseSuccessor())
+ return false;
+ Succ = Case.getCaseSuccessor();
+ }
+
+ // Determine predicate for the missing case.
+ ICmpInst::Predicate Pred;
+ assert(Missing.size() == 1 && "Should have one case left");
+ switch (*Missing.begin()) {
+ case 1:
+ Pred = ICmpInst::ICMP_UGT;
+ break;
+ case 0:
+ Pred = ICmpInst::ICMP_EQ;
+ break;
+ case -1:
+ Pred = ICmpInst::ICMP_ULT;
+ break;
+ }
+ if (Cmp->isSigned())
+ Pred = ICmpInst::getSignedPredicate(Pred);
+
+ // The dominator tree does not change, because it treats multi-edges like
+ // a single edge anyway.
+ Builder.SetInsertPoint(SI->getIterator());
+ Value *ICmp = Builder.CreateICmp(Pred, Cmp->getLHS(), Cmp->getRHS());
+ Builder.CreateCondBr(ICmp, SI->getDefaultDest(), Succ);
+ Succ->removePredecessor(SI->getParent());
+ SI->eraseFromParent();
+ Cmp->eraseFromParent();
+ return true;
+}
+
bool SimplifyCFGOpt::simplifySwitch(SwitchInst *SI, IRBuilder<> &Builder) {
BasicBlock *BB = SI->getParent();
@@ -7163,6 +7216,9 @@ bool SimplifyCFGOpt::simplifySwitch(SwitchInst *SI, IRBuilder<> &Builder) {
if (eliminateDeadSwitchCases(SI, DTU, Options.AC, DL))
return requestResimplify();
+ if (simplifySwitchOfCmpIntrinsic(SI, Builder))
+ return requestResimplify();
+
if (trySwitchToSelect(SI, Builder, DTU, DL, TTI))
return requestResimplify();
diff --git a/llvm/test/Transforms/SimplifyCFG/switch-on-cmp.ll b/llvm/test/Transforms/SimplifyCFG/switch-on-cmp.ll
index 1ce18533d156d0..a9b7a0b9e2f096 100644
--- a/llvm/test/Transforms/SimplifyCFG/switch-on-cmp.ll
+++ b/llvm/test/Transforms/SimplifyCFG/switch-on-cmp.ll
@@ -4,11 +4,8 @@
define void @ucmp_gt1(i32 %a, i32 %b) {
; CHECK-LABEL: define void @ucmp_gt1(
; CHECK-SAME: i32 [[A:%.*]], i32 [[B:%.*]]) {
-; CHECK-NEXT: [[RES:%.*]] = call i8 @llvm.ucmp.i8.i32(i32 [[A]], i32 [[B]])
-; CHECK-NEXT: switch i8 [[RES]], label %[[BB1:.*]] [
-; CHECK-NEXT: i8 -1, label %[[BB2:.*]]
-; CHECK-NEXT: i8 0, label %[[BB2]]
-; CHECK-NEXT: ]
+; CHECK-NEXT: [[TMP1:%.*]] = icmp ugt i32 [[A]], [[B]]
+; CHECK-NEXT: br i1 [[TMP1]], label %[[BB1:.*]], label %[[BB2:.*]]
; CHECK: [[BB1]]:
; CHECK-NEXT: call void @foo()
; CHECK-NEXT: br label %[[BB2]]
@@ -32,11 +29,8 @@ bb2:
define void @ucmp_gt2(i32 %a, i32 %b) {
; CHECK-LABEL: define void @ucmp_gt2(
; CHECK-SAME: i32 [[A:%.*]], i32 [[B:%.*]]) {
-; CHECK-NEXT: [[RES:%.*]] = call i8 @llvm.ucmp.i8.i32(i32 [[A]], i32 [[B]])
-; CHECK-NEXT: switch i8 [[RES]], label %[[BB1:.*]] [
-; CHECK-NEXT: i8 0, label %[[BB2:.*]]
-; CHECK-NEXT: i8 -1, label %[[BB2]]
-; CHECK-NEXT: ]
+; CHECK-NEXT: [[TMP1:%.*]] = icmp ugt i32 [[A]], [[B]]
+; CHECK-NEXT: br i1 [[TMP1]], label %[[BB1:.*]], label %[[BB2:.*]]
; CHECK: [[BB1]]:
; CHECK-NEXT: call void @foo()
; CHECK-NEXT: br label %[[BB2]]
@@ -60,11 +54,8 @@ bb2:
define void @ucmp_lt1(i32 %a, i32 %b) {
; CHECK-LABEL: define void @ucmp_lt1(
; CHECK-SAME: i32 [[A:%.*]], i32 [[B:%.*]]) {
-; CHECK-NEXT: [[RES:%.*]] = call i8 @llvm.ucmp.i8.i32(i32 [[A]], i32 [[B]])
-; CHECK-NEXT: switch i8 [[RES]], label %[[BB2:.*]] [
-; CHECK-NEXT: i8 1, label %[[BB1:.*]]
-; CHECK-NEXT: i8 0, label %[[BB1]]
-; CHECK-NEXT: ]
+; CHECK-NEXT: [[TMP1:%.*]] = icmp ult i32 [[A]], [[B]]
+; CHECK-NEXT: br i1 [[TMP1]], label %[[BB2:.*]], label %[[BB1:.*]]
; CHECK: [[BB1]]:
; CHECK-NEXT: call void @foo()
; CHECK-NEXT: br label %[[BB2]]
@@ -88,11 +79,8 @@ bb2:
define void @ucmp_lt2(i32 %a, i32 %b) {
; CHECK-LABEL: define void @ucmp_lt2(
; CHECK-SAME: i32 [[A:%.*]], i32 [[B:%.*]]) {
-; CHECK-NEXT: [[RES:%.*]] = call i8 @llvm.ucmp.i8.i32(i32 [[A]], i32 [[B]])
-; CHECK-NEXT: switch i8 [[RES]], label %[[BB2:.*]] [
-; CHECK-NEXT: i8 0, label %[[BB1:.*]]
-; CHECK-NEXT: i8 1, label %[[BB1]]
-; CHECK-NEXT: ]
+; CHECK-NEXT: [[TMP1:%.*]] = icmp ult i32 [[A]], [[B]]
+; CHECK-NEXT: br i1 [[TMP1]], label %[[BB2:.*]], label %[[BB1:.*]]
; CHECK: [[BB1]]:
; CHECK-NEXT: call void @foo()
; CHECK-NEXT: br label %[[BB2]]
@@ -116,11 +104,8 @@ bb2:
define void @ucmp_eq1(i32 %a, i32 %b) {
; CHECK-LABEL: define void @ucmp_eq1(
; CHECK-SAME: i32 [[A:%.*]], i32 [[B:%.*]]) {
-; CHECK-NEXT: [[RES:%.*]] = call i8 @llvm.ucmp.i8.i32(i32 [[A]], i32 [[B]])
-; CHECK-NEXT: switch i8 [[RES]], label %[[BB1:.*]] [
-; CHECK-NEXT: i8 -1, label %[[BB2:.*]]
-; CHECK-NEXT: i8 1, label %[[BB2]]
-; CHECK-NEXT: ]
+; CHECK-NEXT: [[TMP1:%.*]] = icmp eq i32 [[A]], [[B]]
+; CHECK-NEXT: br i1 [[TMP1]], label %[[BB1:.*]], label %[[BB2:.*]]
; CHECK: [[BB1]]:
; CHECK-NEXT: call void @foo()
; CHECK-NEXT: br label %[[BB2]]
@@ -144,11 +129,8 @@ bb2:
define void @ucmp_eq2(i32 %a, i32 %b) {
; CHECK-LABEL: define void @ucmp_eq2(
; CHECK-SAME: i32 [[A:%.*]], i32 [[B:%.*]]) {
-; CHECK-NEXT: [[RES:%.*]] = call i8 @llvm.ucmp.i8.i32(i32 [[A]], i32 [[B]])
-; CHECK-NEXT: switch i8 [[RES]], label %[[BB1:.*]] [
-; CHECK-NEXT: i8 1, label %[[BB2:.*]]
-; CHECK-NEXT: i8 -1, label %[[BB2]]
-; CHECK-NEXT: ]
+; CHECK-NEXT: [[TMP1:%.*]] = icmp eq i32 [[A]], [[B]]
+; CHECK-NEXT: br i1 [[TMP1]], label %[[BB1:.*]], label %[[BB2:.*]]
; CHECK: [[BB1]]:
; CHECK-NEXT: call void @foo()
; CHECK-NEXT: br label %[[BB2]]
@@ -172,11 +154,8 @@ bb2:
define void @scmp_gt1(i32 %a, i32 %b) {
; CHECK-LABEL: define void @scmp_gt1(
; CHECK-SAME: i32 [[A:%.*]], i32 [[B:%.*]]) {
-; CHECK-NEXT: [[RES:%.*]] = call i8 @llvm.scmp.i8.i32(i32 [[A]], i32 [[B]])
-; CHECK-NEXT: switch i8 [[RES]], label %[[BB1:.*]] [
-; CHECK-NEXT: i8 -1, label %[[BB2:.*]]
-; CHECK-NEXT: i8 0, label %[[BB2]]
-; CHECK-NEXT: ]
+; CHECK-NEXT: [[TMP1:%.*]] = icmp sgt i32 [[A]], [[B]]
+; CHECK-NEXT: br i1 [[TMP1]], label %[[BB1:.*]], label %[[BB2:.*]]
; CHECK: [[BB1]]:
; CHECK-NEXT: call void @foo()
; CHECK-NEXT: br label %[[BB2]]
@@ -200,11 +179,8 @@ bb2:
define void @scmp_gt2(i32 %a, i32 %b) {
; CHECK-LABEL: define void @scmp_gt2(
; CHECK-SAME: i32 [[A:%.*]], i32 [[B:%.*]]) {
-; CHECK-NEXT: [[RES:%.*]] = call i8 @llvm.scmp.i8.i32(i32 [[A]], i32 [[B]])
-; CHECK-NEXT: switch i8 [[RES]], label %[[BB1:.*]] [
-; CHECK-NEXT: i8 0, label %[[BB2:.*]]
-; CHECK-NEXT: i8 -1, label %[[BB2]]
-; CHECK-NEXT: ]
+; CHECK-NEXT: [[TMP1:%.*]] = icmp sgt i32 [[A]], [[B]]
+; CHECK-NEXT: br i1 [[TMP1]], label %[[BB1:.*]], label %[[BB2:.*]]
; CHECK: [[BB1]]:
; CHECK-NEXT: call void @foo()
; CHECK-NEXT: br label %[[BB2]]
@@ -259,16 +235,13 @@ define i32 @ucmp_gt_phi(i32 %a, i32 %b) {
; CHECK-LABEL: define i32 @ucmp_gt_phi(
; CHECK-SAME: i32 [[A:%.*]], i32 [[B:%.*]]) {
; CHECK-NEXT: [[ENTRY:.*]]:
-; CHECK-NEXT: [[RES:%.*]] = call i8 @llvm.ucmp.i8.i32(i32 [[A]], i32 [[B]])
-; CHECK-NEXT: switch i8 [[RES]], label %[[BB1:.*]] [
-; CHECK-NEXT: i8 -1, label %[[BB2:.*]]
-; CHECK-NEXT: i8 0, label %[[BB2]]
-; CHECK-NEXT: ]
+; CHECK-NEXT: [[TMP0:%.*]] = icmp ugt i32 [[A]], [[B]]
+; CHECK-NEXT: br i1 [[TMP0]], label %[[BB1:.*]], label %[[BB2:.*]]
; CHECK: [[BB1]]:
; CHECK-NEXT: call void @foo()
; CHECK-NEXT: br label %[[BB2]]
; CHECK: [[BB2]]:
-; CHECK-NEXT: [[PHI:%.*]] = phi i32 [ 0, %[[BB1]] ], [ 1, %[[ENTRY]] ], [ 1, %[[ENTRY]] ]
+; CHECK-NEXT: [[PHI:%.*]] = phi i32 [ 0, %[[BB1]] ], [ 1, %[[ENTRY]] ]
; CHECK-NEXT: ret i32 [[PHI]]
;
entry:
``````````
</details>
https://github.com/llvm/llvm-project/pull/105636
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