[llvm] [SimplifyCFG] Improve FoldTwoEntryPHINode when one of phi values is undef (PR #69021)
Yingwei Zheng via llvm-commits
llvm-commits at lists.llvm.org
Sat Oct 14 04:21:08 PDT 2023
https://github.com/dtcxzyw updated https://github.com/llvm/llvm-project/pull/69021
>From 35df6d09ce355e2e4db5d00bcc08c7b3776923d7 Mon Sep 17 00:00:00 2001
From: Yingwei Zheng <dtcxzyw2333 at gmail.com>
Date: Sat, 14 Oct 2023 02:28:56 +0800
Subject: [PATCH 1/3] [SimplifyCFG] Add pre-commit tests for PR67342. NFC.
---
llvm/test/Transforms/SimplifyCFG/pr67342.ll | 52 +++++++++++++++++++++
1 file changed, 52 insertions(+)
create mode 100644 llvm/test/Transforms/SimplifyCFG/pr67342.ll
diff --git a/llvm/test/Transforms/SimplifyCFG/pr67342.ll b/llvm/test/Transforms/SimplifyCFG/pr67342.ll
new file mode 100644
index 000000000000000..e278c626acf1738
--- /dev/null
+++ b/llvm/test/Transforms/SimplifyCFG/pr67342.ll
@@ -0,0 +1,52 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 3
+; RUN: opt -S -passes=simplifycfg < %s | FileCheck %s
+
+; Tests from PR67342
+define i16 @test1(i32 %err) {
+; CHECK-LABEL: define i16 @test1(
+; CHECK-SAME: i32 [[ERR:%.*]]) {
+; CHECK-NEXT: bb3:
+; CHECK-NEXT: [[_3:%.*]] = icmp slt i32 [[ERR]], 0
+; CHECK-NEXT: [[OK:%.*]] = trunc i32 [[ERR]] to i16
+; CHECK-NEXT: [[R_SROA_3_0:%.*]] = select i1 [[_3]], i16 undef, i16 [[OK]]
+; CHECK-NEXT: ret i16 [[R_SROA_3_0]]
+;
+ %_3 = icmp slt i32 %err, 0
+ br i1 %_3, label %bb1, label %bb2
+
+bb2:
+ %ok = trunc i32 %err to i16
+ br label %bb3
+
+bb1:
+ br label %bb3
+
+bb3:
+ %r.sroa.3.0 = phi i16 [ undef, %bb1 ], [ %ok, %bb2 ]
+ ret i16 %r.sroa.3.0
+}
+
+; commuted test
+define i16 @test2(i32 %err) {
+; CHECK-LABEL: define i16 @test2(
+; CHECK-SAME: i32 [[ERR:%.*]]) {
+; CHECK-NEXT: bb3:
+; CHECK-NEXT: [[_3:%.*]] = icmp slt i32 [[ERR]], 0
+; CHECK-NEXT: [[OK:%.*]] = trunc i32 [[ERR]] to i16
+; CHECK-NEXT: [[R_SROA_3_0:%.*]] = select i1 [[_3]], i16 [[OK]], i16 undef
+; CHECK-NEXT: ret i16 [[R_SROA_3_0]]
+;
+ %_3 = icmp slt i32 %err, 0
+ br i1 %_3, label %bb1, label %bb2
+
+bb2:
+ br label %bb3
+
+bb1:
+ %ok = trunc i32 %err to i16
+ br label %bb3
+
+bb3:
+ %r.sroa.3.0 = phi i16 [ %ok, %bb1 ], [ undef, %bb2 ]
+ ret i16 %r.sroa.3.0
+}
>From e3aa1dcc937e11b5f073224cbfbcbc0c677bd928 Mon Sep 17 00:00:00 2001
From: Yingwei Zheng <dtcxzyw2333 at gmail.com>
Date: Sat, 14 Oct 2023 02:32:08 +0800
Subject: [PATCH 2/3] [SimplifyCFG] Improve FoldTwoEntryPHINode when one of phi
values is undef
---
llvm/lib/Transforms/Utils/SimplifyCFG.cpp | 19 ++++++++++++++++---
llvm/test/Transforms/SimplifyCFG/pr67342.ll | 6 ++----
2 files changed, 18 insertions(+), 7 deletions(-)
diff --git a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
index 35fead111aa9666..bab5363e63a85eb 100644
--- a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -3543,9 +3543,22 @@ static bool FoldTwoEntryPHINode(PHINode *PN, const TargetTransformInfo &TTI,
Value *TrueVal = PN->getIncomingValueForBlock(IfTrue);
Value *FalseVal = PN->getIncomingValueForBlock(IfFalse);
- Value *Sel = Builder.CreateSelect(IfCond, TrueVal, FalseVal, "", DomBI);
- PN->replaceAllUsesWith(Sel);
- Sel->takeName(PN);
+ Value *ReplaceVal = nullptr;
+ if (isa<UndefValue>(TrueVal) &&
+ isGuaranteedNotToBePoison(FalseVal, /*AC*/ nullptr,
+ IfFalse->getTerminator(),
+ DTU ? &DTU->getDomTree() : nullptr, 0)) {
+ ReplaceVal = FalseVal;
+ } else if (isa<UndefValue>(FalseVal) &&
+ isGuaranteedNotToBePoison(
+ TrueVal, /*AC*/ nullptr, IfFalse->getTerminator(),
+ DTU ? &DTU->getDomTree() : nullptr, 0)) {
+ ReplaceVal = TrueVal;
+ } else {
+ ReplaceVal = Builder.CreateSelect(IfCond, TrueVal, FalseVal, "", DomBI);
+ ReplaceVal->takeName(PN);
+ }
+ PN->replaceAllUsesWith(ReplaceVal);
PN->eraseFromParent();
}
diff --git a/llvm/test/Transforms/SimplifyCFG/pr67342.ll b/llvm/test/Transforms/SimplifyCFG/pr67342.ll
index e278c626acf1738..c2c9f460d8e5f9e 100644
--- a/llvm/test/Transforms/SimplifyCFG/pr67342.ll
+++ b/llvm/test/Transforms/SimplifyCFG/pr67342.ll
@@ -8,8 +8,7 @@ define i16 @test1(i32 %err) {
; CHECK-NEXT: bb3:
; CHECK-NEXT: [[_3:%.*]] = icmp slt i32 [[ERR]], 0
; CHECK-NEXT: [[OK:%.*]] = trunc i32 [[ERR]] to i16
-; CHECK-NEXT: [[R_SROA_3_0:%.*]] = select i1 [[_3]], i16 undef, i16 [[OK]]
-; CHECK-NEXT: ret i16 [[R_SROA_3_0]]
+; CHECK-NEXT: ret i16 [[OK]]
;
%_3 = icmp slt i32 %err, 0
br i1 %_3, label %bb1, label %bb2
@@ -33,8 +32,7 @@ define i16 @test2(i32 %err) {
; CHECK-NEXT: bb3:
; CHECK-NEXT: [[_3:%.*]] = icmp slt i32 [[ERR]], 0
; CHECK-NEXT: [[OK:%.*]] = trunc i32 [[ERR]] to i16
-; CHECK-NEXT: [[R_SROA_3_0:%.*]] = select i1 [[_3]], i16 [[OK]], i16 undef
-; CHECK-NEXT: ret i16 [[R_SROA_3_0]]
+; CHECK-NEXT: ret i16 [[OK]]
;
%_3 = icmp slt i32 %err, 0
br i1 %_3, label %bb1, label %bb2
>From f64cfee5666472a67e8b3c733aa2e75f96273b46 Mon Sep 17 00:00:00 2001
From: Yingwei Zheng <dtcxzyw2333 at gmail.com>
Date: Sat, 14 Oct 2023 19:05:12 +0800
Subject: [PATCH 3/3] fixup! [SimplifyCFG] Improve FoldTwoEntryPHINode when one
of phi values is undef
---
llvm/lib/Transforms/Utils/SimplifyCFG.cpp | 15 +++++++--------
1 file changed, 7 insertions(+), 8 deletions(-)
diff --git a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
index bab5363e63a85eb..a8c4b1cc34c6cff 100644
--- a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -3376,7 +3376,8 @@ static bool FoldCondBranchOnValueKnownInPredecessor(BranchInst *BI,
/// Given a BB that starts with the specified two-entry PHI node,
/// see if we can eliminate it.
static bool FoldTwoEntryPHINode(PHINode *PN, const TargetTransformInfo &TTI,
- DomTreeUpdater *DTU, const DataLayout &DL) {
+ DomTreeUpdater *DTU, const DataLayout &DL,
+ AssumptionCache *AC) {
// Ok, this is a two entry PHI node. Check to see if this is a simple "if
// statement", which has a very simple dominance structure. Basically, we
// are trying to find the condition that is being branched on, which
@@ -3545,14 +3546,12 @@ static bool FoldTwoEntryPHINode(PHINode *PN, const TargetTransformInfo &TTI,
Value *ReplaceVal = nullptr;
if (isa<UndefValue>(TrueVal) &&
- isGuaranteedNotToBePoison(FalseVal, /*AC*/ nullptr,
- IfFalse->getTerminator(),
- DTU ? &DTU->getDomTree() : nullptr, 0)) {
+ isGuaranteedNotToBePoison(FalseVal, AC, IfFalse->getTerminator(),
+ /*DT*/ nullptr, /*Depth*/ 0)) {
ReplaceVal = FalseVal;
} else if (isa<UndefValue>(FalseVal) &&
- isGuaranteedNotToBePoison(
- TrueVal, /*AC*/ nullptr, IfFalse->getTerminator(),
- DTU ? &DTU->getDomTree() : nullptr, 0)) {
+ isGuaranteedNotToBePoison(TrueVal, AC, IfTrue->getTerminator(),
+ /*DT*/ nullptr, /*Depth*/ 0)) {
ReplaceVal = TrueVal;
} else {
ReplaceVal = Builder.CreateSelect(IfCond, TrueVal, FalseVal, "", DomBI);
@@ -7419,7 +7418,7 @@ bool SimplifyCFGOpt::simplifyOnce(BasicBlock *BB) {
// eliminate it, do so now.
if (auto *PN = dyn_cast<PHINode>(BB->begin()))
if (PN->getNumIncomingValues() == 2)
- if (FoldTwoEntryPHINode(PN, TTI, DTU, DL))
+ if (FoldTwoEntryPHINode(PN, TTI, DTU, DL, Options.AC))
return true;
}
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