[llvm] [ValueTracking] Compute known FPClass from signbit idiom (PR #80740)
Yingwei Zheng via llvm-commits
llvm-commits at lists.llvm.org
Wed Feb 14 03:20:49 PST 2024
https://github.com/dtcxzyw updated https://github.com/llvm/llvm-project/pull/80740
>From 6a53e1b1724f44da57cff8f0d13889427b40ef74 Mon Sep 17 00:00:00 2001
From: Yingwei Zheng <dtcxzyw2333 at gmail.com>
Date: Tue, 13 Feb 2024 20:58:41 +0800
Subject: [PATCH 1/4] [ValueTracking] Add pre-commit tests. NFC.
---
.../InstCombine/fpclass-from-dom-cond.ll | 116 ++++++++++++++++++
1 file changed, 116 insertions(+)
diff --git a/llvm/test/Transforms/InstCombine/fpclass-from-dom-cond.ll b/llvm/test/Transforms/InstCombine/fpclass-from-dom-cond.ll
index 5d4840159dc9a0..6f4cf092cfbc6f 100644
--- a/llvm/test/Transforms/InstCombine/fpclass-from-dom-cond.ll
+++ b/llvm/test/Transforms/InstCombine/fpclass-from-dom-cond.ll
@@ -320,3 +320,119 @@ if.else:
%ret = call i1 @llvm.is.fpclass.f32(float %x, i32 783)
ret i1 %ret
}
+
+define float @test_signbit_check(float %x, i1 %cond) {
+; CHECK-LABEL: define float @test_signbit_check(
+; CHECK-SAME: float [[X:%.*]], i1 [[COND:%.*]]) {
+; CHECK-NEXT: [[I32:%.*]] = bitcast float [[X]] to i32
+; CHECK-NEXT: [[CMP:%.*]] = icmp slt i32 [[I32]], 0
+; CHECK-NEXT: br i1 [[CMP]], label [[IF_THEN1:%.*]], label [[IF_ELSE:%.*]]
+; CHECK: if.then1:
+; CHECK-NEXT: [[FNEG:%.*]] = fneg float [[X]]
+; CHECK-NEXT: br label [[IF_END:%.*]]
+; CHECK: if.else:
+; CHECK-NEXT: br i1 [[COND]], label [[IF_THEN2:%.*]], label [[IF_END]]
+; CHECK: if.then2:
+; CHECK-NEXT: br label [[IF_END]]
+; CHECK: if.end:
+; CHECK-NEXT: [[VALUE:%.*]] = phi float [ [[FNEG]], [[IF_THEN1]] ], [ [[X]], [[IF_THEN2]] ], [ [[X]], [[IF_ELSE]] ]
+; CHECK-NEXT: [[RET:%.*]] = call float @llvm.fabs.f32(float [[VALUE]])
+; CHECK-NEXT: ret float [[RET]]
+;
+ %i32 = bitcast float %x to i32
+ %cmp = icmp slt i32 %i32, 0
+ br i1 %cmp, label %if.then1, label %if.else
+
+if.then1:
+ %fneg = fneg float %x
+ br label %if.end
+
+if.else:
+ br i1 %cond, label %if.then2, label %if.end
+
+if.then2:
+ br label %if.end
+
+if.end:
+ %value = phi float [ %fneg, %if.then1 ], [ %x, %if.then2 ], [ %x, %if.else ]
+ %ret = call float @llvm.fabs.f32(float %value)
+ ret float %ret
+}
+
+define float @test_signbit_check_fail(float %x, i1 %cond) {
+; CHECK-LABEL: define float @test_signbit_check_fail(
+; CHECK-SAME: float [[X:%.*]], i1 [[COND:%.*]]) {
+; CHECK-NEXT: [[I32:%.*]] = bitcast float [[X]] to i32
+; CHECK-NEXT: [[CMP:%.*]] = icmp slt i32 [[I32]], 0
+; CHECK-NEXT: br i1 [[CMP]], label [[IF_THEN1:%.*]], label [[IF_ELSE:%.*]]
+; CHECK: if.then1:
+; CHECK-NEXT: [[FNEG:%.*]] = fneg float [[X]]
+; CHECK-NEXT: br label [[IF_END:%.*]]
+; CHECK: if.else:
+; CHECK-NEXT: br i1 [[COND]], label [[IF_THEN2:%.*]], label [[IF_END]]
+; CHECK: if.then2:
+; CHECK-NEXT: [[FNEG2:%.*]] = fneg float [[X]]
+; CHECK-NEXT: br label [[IF_END]]
+; CHECK: if.end:
+; CHECK-NEXT: [[VALUE:%.*]] = phi float [ [[FNEG]], [[IF_THEN1]] ], [ [[FNEG2]], [[IF_THEN2]] ], [ [[X]], [[IF_ELSE]] ]
+; CHECK-NEXT: [[RET:%.*]] = call float @llvm.fabs.f32(float [[VALUE]])
+; CHECK-NEXT: ret float [[RET]]
+;
+ %i32 = bitcast float %x to i32
+ %cmp = icmp slt i32 %i32, 0
+ br i1 %cmp, label %if.then1, label %if.else
+
+if.then1:
+ %fneg = fneg float %x
+ br label %if.end
+
+if.else:
+ br i1 %cond, label %if.then2, label %if.end
+
+if.then2:
+ %fneg2 = fneg float %x
+ br label %if.end
+
+if.end:
+ %value = phi float [ %fneg, %if.then1 ], [ %fneg2, %if.then2 ], [ %x, %if.else ]
+ %ret = call float @llvm.fabs.f32(float %value)
+ ret float %ret
+}
+
+define <2 x float> @test_signbit_check_wrong_type(<2 x float> %x, i1 %cond) {
+; CHECK-LABEL: define <2 x float> @test_signbit_check_wrong_type(
+; CHECK-SAME: <2 x float> [[X:%.*]], i1 [[COND:%.*]]) {
+; CHECK-NEXT: [[I32:%.*]] = bitcast <2 x float> [[X]] to i64
+; CHECK-NEXT: [[CMP:%.*]] = icmp slt i64 [[I32]], 0
+; CHECK-NEXT: br i1 [[CMP]], label [[IF_THEN1:%.*]], label [[IF_ELSE:%.*]]
+; CHECK: if.then1:
+; CHECK-NEXT: [[FNEG:%.*]] = fneg <2 x float> [[X]]
+; CHECK-NEXT: br label [[IF_END:%.*]]
+; CHECK: if.else:
+; CHECK-NEXT: br i1 [[COND]], label [[IF_THEN2:%.*]], label [[IF_END]]
+; CHECK: if.then2:
+; CHECK-NEXT: br label [[IF_END]]
+; CHECK: if.end:
+; CHECK-NEXT: [[VALUE:%.*]] = phi <2 x float> [ [[FNEG]], [[IF_THEN1]] ], [ [[X]], [[IF_THEN2]] ], [ [[X]], [[IF_ELSE]] ]
+; CHECK-NEXT: [[RET:%.*]] = call <2 x float> @llvm.fabs.v2f32(<2 x float> [[VALUE]])
+; CHECK-NEXT: ret <2 x float> [[RET]]
+;
+ %i32 = bitcast <2 x float> %x to i64
+ %cmp = icmp slt i64 %i32, 0
+ br i1 %cmp, label %if.then1, label %if.else
+
+if.then1:
+ %fneg = fneg <2 x float> %x
+ br label %if.end
+
+if.else:
+ br i1 %cond, label %if.then2, label %if.end
+
+if.then2:
+ br label %if.end
+
+if.end:
+ %value = phi <2 x float> [ %fneg, %if.then1 ], [ %x, %if.then2 ], [ %x, %if.else ]
+ %ret = call <2 x float> @llvm.fabs.v2f32(<2 x float> %value)
+ ret <2 x float> %ret
+}
>From e4e88ce4492996446d7701efff204ce36565b900 Mon Sep 17 00:00:00 2001
From: Yingwei Zheng <dtcxzyw2333 at gmail.com>
Date: Tue, 13 Feb 2024 21:18:20 +0800
Subject: [PATCH 2/4] [ValueTracking] Handle signbit idiom in
`computeKnownFPClassFromCond`
---
llvm/lib/Analysis/DomConditionCache.cpp | 4 ++++
llvm/lib/Analysis/ValueTracking.cpp | 15 ++++++++++++++-
.../InstCombine/fpclass-from-dom-cond.ll | 3 +--
3 files changed, 19 insertions(+), 3 deletions(-)
diff --git a/llvm/lib/Analysis/DomConditionCache.cpp b/llvm/lib/Analysis/DomConditionCache.cpp
index c07a8a76f111df..66ad2b8d86dc39 100644
--- a/llvm/lib/Analysis/DomConditionCache.cpp
+++ b/llvm/lib/Analysis/DomConditionCache.cpp
@@ -66,6 +66,10 @@ static void findAffectedValues(Value *Cond,
// A > C3 && A < C4.
if (match(A, m_Add(m_Value(X), m_ConstantInt())))
AddAffected(X);
+ // Handle icmp slt/sgt (bitcast X to int), 0/-1
+ if (match(A, m_ElementWiseBitCast(m_Value(X))) &&
+ (Pred == ICmpInst::ICMP_SLT || Pred == ICmpInst::ICMP_SGT))
+ Affected.push_back(X);
}
} else if (match(Cond, m_CombineOr(m_FCmp(Pred, m_Value(A), m_Constant()),
m_Intrinsic<Intrinsic::is_fpclass>(
diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index 6c42facea3b2b3..9ed204f7b2c5db 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -4272,7 +4272,7 @@ static void computeKnownFPClassFromCond(const Value *V, Value *Cond,
Value *LHS;
uint64_t ClassVal = 0;
const APFloat *CRHS;
- // TODO: handle sign-bit check idiom
+ const APInt *RHS;
if (match(Cond, m_FCmp(Pred, m_Value(LHS), m_APFloat(CRHS)))) {
auto [CmpVal, MaskIfTrue, MaskIfFalse] = fcmpImpliesClass(
Pred, *CxtI->getParent()->getParent(), LHS, *CRHS, LHS != V);
@@ -4282,6 +4282,19 @@ static void computeKnownFPClassFromCond(const Value *V, Value *Cond,
m_Value(LHS), m_ConstantInt(ClassVal)))) {
FPClassTest Mask = static_cast<FPClassTest>(ClassVal);
KnownFromContext.knownNot(CondIsTrue ? ~Mask : Mask);
+ } else if (match(Cond, m_ICmp(Pred, m_ElementWiseBitCast(m_Value(LHS)),
+ m_APInt(RHS)))) {
+ bool TrueIfSigned;
+ if (Pred == ICmpInst::ICMP_SLT && RHS->isZero())
+ TrueIfSigned = true;
+ else if (Pred == ICmpInst::ICMP_SGT && RHS->isAllOnes())
+ TrueIfSigned = false;
+ else
+ return;
+ if (TrueIfSigned == CondIsTrue)
+ KnownFromContext.signBitMustBeOne();
+ else
+ KnownFromContext.signBitMustBeZero();
}
}
diff --git a/llvm/test/Transforms/InstCombine/fpclass-from-dom-cond.ll b/llvm/test/Transforms/InstCombine/fpclass-from-dom-cond.ll
index 6f4cf092cfbc6f..d40cd7fd503ecc 100644
--- a/llvm/test/Transforms/InstCombine/fpclass-from-dom-cond.ll
+++ b/llvm/test/Transforms/InstCombine/fpclass-from-dom-cond.ll
@@ -336,8 +336,7 @@ define float @test_signbit_check(float %x, i1 %cond) {
; CHECK-NEXT: br label [[IF_END]]
; CHECK: if.end:
; CHECK-NEXT: [[VALUE:%.*]] = phi float [ [[FNEG]], [[IF_THEN1]] ], [ [[X]], [[IF_THEN2]] ], [ [[X]], [[IF_ELSE]] ]
-; CHECK-NEXT: [[RET:%.*]] = call float @llvm.fabs.f32(float [[VALUE]])
-; CHECK-NEXT: ret float [[RET]]
+; CHECK-NEXT: ret float [[VALUE]]
;
%i32 = bitcast float %x to i32
%cmp = icmp slt i32 %i32, 0
>From 57ec61d6eeda08bbddae395530fad88ee9c8074d Mon Sep 17 00:00:00 2001
From: Yingwei Zheng <dtcxzyw2333 at gmail.com>
Date: Wed, 14 Feb 2024 09:20:48 +0800
Subject: [PATCH 3/4] fixup! [ValueTracking] Handle signbit idiom in
`computeKnownFPClassFromCond`
---
llvm/lib/Analysis/DomConditionCache.cpp | 7 ++++---
1 file changed, 4 insertions(+), 3 deletions(-)
diff --git a/llvm/lib/Analysis/DomConditionCache.cpp b/llvm/lib/Analysis/DomConditionCache.cpp
index 66ad2b8d86dc39..274f3ff44b2a6f 100644
--- a/llvm/lib/Analysis/DomConditionCache.cpp
+++ b/llvm/lib/Analysis/DomConditionCache.cpp
@@ -66,9 +66,10 @@ static void findAffectedValues(Value *Cond,
// A > C3 && A < C4.
if (match(A, m_Add(m_Value(X), m_ConstantInt())))
AddAffected(X);
- // Handle icmp slt/sgt (bitcast X to int), 0/-1
- if (match(A, m_ElementWiseBitCast(m_Value(X))) &&
- (Pred == ICmpInst::ICMP_SLT || Pred == ICmpInst::ICMP_SGT))
+ // Handle icmp slt/sgt (bitcast X to int), 0/-1, which is supported by
+ // computeKnownFPClass().
+ if ((Pred == ICmpInst::ICMP_SLT || Pred == ICmpInst::ICMP_SGT) &&
+ match(A, m_ElementWiseBitCast(m_Value(X))))
Affected.push_back(X);
}
} else if (match(Cond, m_CombineOr(m_FCmp(Pred, m_Value(A), m_Constant()),
>From 041218bf5491996edd828cc15b3aec5a59ddc636 Mon Sep 17 00:00:00 2001
From: Yingwei Zheng <dtcxzyw2333 at gmail.com>
Date: Wed, 14 Feb 2024 19:20:13 +0800
Subject: [PATCH 4/4] [ValueTracking] Use the `isSignBitCheck` helper.
---
llvm/lib/Analysis/ValueTracking.cpp | 6 +-----
1 file changed, 1 insertion(+), 5 deletions(-)
diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index 9ed204f7b2c5db..cc1d5b74dcfc53 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -4285,11 +4285,7 @@ static void computeKnownFPClassFromCond(const Value *V, Value *Cond,
} else if (match(Cond, m_ICmp(Pred, m_ElementWiseBitCast(m_Value(LHS)),
m_APInt(RHS)))) {
bool TrueIfSigned;
- if (Pred == ICmpInst::ICMP_SLT && RHS->isZero())
- TrueIfSigned = true;
- else if (Pred == ICmpInst::ICMP_SGT && RHS->isAllOnes())
- TrueIfSigned = false;
- else
+ if (!isSignBitCheck(Pred, *RHS, TrueIfSigned))
return;
if (TrueIfSigned == CondIsTrue)
KnownFromContext.signBitMustBeOne();
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