[llvm] [LVI][CVP] Fold trunc bittest to true/false. (PR #124480)
Andreas Jonson via llvm-commits
llvm-commits at lists.llvm.org
Sun Jan 26 12:23:55 PST 2025
https://github.com/andjo403 updated https://github.com/llvm/llvm-project/pull/124480
>From 137baab50595c0f635b6edd3c47b89385c9af97f Mon Sep 17 00:00:00 2001
From: Andreas Jonson <andjo403 at hotmail.com>
Date: Sun, 26 Jan 2025 21:23:35 +0100
Subject: [PATCH] [LVI][CVP] Fold trunc bittest to true/false.
---
llvm/lib/Analysis/LazyValueInfo.cpp | 19 ++++++++++++++++
.../Scalar/CorrelatedValuePropagation.cpp | 18 +++++++++++++++
.../CorrelatedValuePropagation/icmp.ll | 22 +++++++------------
3 files changed, 45 insertions(+), 14 deletions(-)
diff --git a/llvm/lib/Analysis/LazyValueInfo.cpp b/llvm/lib/Analysis/LazyValueInfo.cpp
index 20f69a0955f51c..05c66457fdaa3e 100644
--- a/llvm/lib/Analysis/LazyValueInfo.cpp
+++ b/llvm/lib/Analysis/LazyValueInfo.cpp
@@ -398,6 +398,8 @@ class LazyValueInfoImpl {
std::optional<ValueLatticeElement>
getValueFromICmpCondition(Value *Val, ICmpInst *ICI, bool isTrueDest,
bool UseBlockValue);
+ std::optional<ValueLatticeElement>
+ getValueFromTrunc(Value *Val, TruncInst *Trunc, bool IsTrueDest);
std::optional<ValueLatticeElement>
getValueFromCondition(Value *Val, Value *Cond, bool IsTrueDest,
@@ -1283,6 +1285,20 @@ std::optional<ValueLatticeElement> LazyValueInfoImpl::getValueFromICmpCondition(
return ValueLatticeElement::getOverdefined();
}
+std::optional<ValueLatticeElement>
+LazyValueInfoImpl::getValueFromTrunc(Value *Val, TruncInst *Trunc,
+ bool IsTrueDest) {
+ assert(Trunc->getType()->isIntegerTy(1));
+
+ Type *Ty = Val->getType();
+ if (!Ty->isIntegerTy() || Trunc->getOperand(0) != Val)
+ return ValueLatticeElement::getOverdefined();
+
+ if (IsTrueDest)
+ return ValueLatticeElement::getNot(Constant::getNullValue(Ty));
+ return ValueLatticeElement::getNot(Constant::getAllOnesValue(Ty));
+}
+
// Handle conditions of the form
// extractvalue(op.with.overflow(%x, C), 1).
static ValueLatticeElement getValueFromOverflowCondition(
@@ -1312,6 +1328,9 @@ LazyValueInfoImpl::getValueFromCondition(Value *Val, Value *Cond,
if (ICmpInst *ICI = dyn_cast<ICmpInst>(Cond))
return getValueFromICmpCondition(Val, ICI, IsTrueDest, UseBlockValue);
+ if (auto *Trunc = dyn_cast<TruncInst>(Cond))
+ return getValueFromTrunc(Val, Trunc, IsTrueDest);
+
if (auto *EVI = dyn_cast<ExtractValueInst>(Cond))
if (auto *WO = dyn_cast<WithOverflowInst>(EVI->getAggregateOperand()))
if (EVI->getNumIndices() == 1 && *EVI->idx_begin() == 1)
diff --git a/llvm/lib/Transforms/Scalar/CorrelatedValuePropagation.cpp b/llvm/lib/Transforms/Scalar/CorrelatedValuePropagation.cpp
index 8e74b8645fad9a..107900cdfdc5d3 100644
--- a/llvm/lib/Transforms/Scalar/CorrelatedValuePropagation.cpp
+++ b/llvm/lib/Transforms/Scalar/CorrelatedValuePropagation.cpp
@@ -348,6 +348,21 @@ static bool processCmp(CmpInst *Cmp, LazyValueInfo *LVI) {
return false;
}
+static bool processTrunc(TruncInst *Trunc, LazyValueInfo *LVI) {
+ Type *Ty = Trunc->getType();
+ if (!Ty->isIntegerTy(1))
+ return false;
+
+ Value *Arg = Trunc->getOperand(0);
+ ConstantRange Res = LVI->getConstantRange(Arg, Trunc, false);
+ if (Res.contains(APInt::getZero(Arg->getType()->getScalarSizeInBits())))
+ return false;
+
+ Trunc->replaceAllUsesWith(ConstantInt::getTrue(Ty));
+ Trunc->eraseFromParent();
+ return true;
+}
+
/// Simplify a switch instruction by removing cases which can never fire. If the
/// uselessness of a case could be determined locally then constant propagation
/// would already have figured it out. Instead, walk the predecessors and
@@ -1239,6 +1254,9 @@ static bool runImpl(Function &F, LazyValueInfo *LVI, DominatorTree *DT,
case Instruction::FCmp:
BBChanged |= processCmp(cast<CmpInst>(&II), LVI);
break;
+ case Instruction::Trunc:
+ BBChanged |= processTrunc(cast<TruncInst>(&II), LVI);
+ break;
case Instruction::Call:
case Instruction::Invoke:
BBChanged |= processCallSite(cast<CallBase>(II), LVI);
diff --git a/llvm/test/Transforms/CorrelatedValuePropagation/icmp.ll b/llvm/test/Transforms/CorrelatedValuePropagation/icmp.ll
index e4de34c339d2de..a470109ff7afbd 100644
--- a/llvm/test/Transforms/CorrelatedValuePropagation/icmp.ll
+++ b/llvm/test/Transforms/CorrelatedValuePropagation/icmp.ll
@@ -1515,10 +1515,8 @@ define void @test_trunc_bittest(i8 %a) {
; CHECK-NEXT: [[TRUNC:%.*]] = trunc i8 [[A:%.*]] to i1
; CHECK-NEXT: br i1 [[TRUNC]], label [[IF_TRUE:%.*]], label [[IF_FALSE:%.*]]
; CHECK: if.true:
-; CHECK-NEXT: [[CMP1:%.*]] = icmp ne i8 [[A]], 0
-; CHECK-NEXT: call void @check1(i1 [[CMP1]])
-; CHECK-NEXT: [[CMP2:%.*]] = icmp eq i8 [[A]], 0
-; CHECK-NEXT: call void @check1(i1 [[CMP2]])
+; CHECK-NEXT: call void @check1(i1 true)
+; CHECK-NEXT: call void @check1(i1 false)
; CHECK-NEXT: ret void
; CHECK: if.false:
; CHECK-NEXT: ret void
@@ -1543,10 +1541,8 @@ define void @test_trunc_not_bittest(i8 %a) {
; CHECK-NEXT: [[NOT:%.*]] = xor i1 [[TRUNC]], true
; CHECK-NEXT: br i1 [[NOT]], label [[IF_FALSE:%.*]], label [[IF_TRUE:%.*]]
; CHECK: if.true:
-; CHECK-NEXT: [[CMP1:%.*]] = icmp ne i8 [[A]], -1
-; CHECK-NEXT: call void @check1(i1 [[CMP1]])
-; CHECK-NEXT: [[CMP2:%.*]] = icmp eq i8 [[A]], -1
-; CHECK-NEXT: call void @check1(i1 [[CMP2]])
+; CHECK-NEXT: call void @check1(i1 true)
+; CHECK-NEXT: call void @check1(i1 false)
; CHECK-NEXT: ret void
; CHECK: if.false:
; CHECK-NEXT: ret void
@@ -1571,8 +1567,7 @@ define void @test_icmp_trunc(i8 %a) {
; CHECK-NEXT: [[CMP1:%.*]] = icmp ne i8 [[A:%.*]], 0
; CHECK-NEXT: br i1 [[CMP1]], label [[IF_TRUE:%.*]], label [[IF_FALSE:%.*]]
; CHECK: if.true:
-; CHECK-NEXT: [[TRUNC:%.*]] = trunc i8 [[A]] to i1
-; CHECK-NEXT: call void @check1(i1 [[TRUNC]])
+; CHECK-NEXT: call void @check1(i1 true)
; CHECK-NEXT: ret void
; CHECK: if.false:
; CHECK-NEXT: ret void
@@ -1594,9 +1589,8 @@ define void @test_icmp_trunc_not(i8 %a) {
; CHECK-NEXT: [[CMP1:%.*]] = icmp eq i8 [[A:%.*]], -1
; CHECK-NEXT: br i1 [[CMP1]], label [[IF_TRUE:%.*]], label [[IF_FALSE:%.*]]
; CHECK: if.true:
-; CHECK-NEXT: [[TRUNC:%.*]] = trunc i8 [[A]] to i1
-; CHECK-NEXT: [[NOT:%.*]] = xor i1 [[TRUNC]], true
-; CHECK-NEXT: call void @check1(i1 [[TRUNC]])
+; CHECK-NEXT: [[NOT:%.*]] = xor i1 true, true
+; CHECK-NEXT: call void @check1(i1 [[NOT]])
; CHECK-NEXT: ret void
; CHECK: if.false:
; CHECK-NEXT: ret void
@@ -1607,7 +1601,7 @@ define void @test_icmp_trunc_not(i8 %a) {
if.true:
%trunc = trunc i8 %a to i1
%not = xor i1 %trunc, true
- call void @check1(i1 %trunc)
+ call void @check1(i1 %not)
ret void
if.false:
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