[llvm] [LVI] Infer non-zero from equality icmp (PR #112838)
Yingwei Zheng via llvm-commits
llvm-commits at lists.llvm.org
Thu Oct 17 22:03:41 PDT 2024
https://github.com/dtcxzyw created https://github.com/llvm/llvm-project/pull/112838
This following pattern is common in loop headers:
```
%101 = sub nuw i64 %78, %98
%103 = icmp eq i64 %78, %98
br i1 %103, label %.thread.i.i, label %.preheader.preheader.i.i
.preheader.preheader.i.i:
%invariant.umin.i.i = call i64 @llvm.umin.i64(i64 %101, i64 9)
%umax.i = call i64 @llvm.umax.i64(i64 %invariant.umin.i.i, i64 1)
br label %.preheader.i.i
.preheader.i.i:
...
%116 = add nuw nsw i64 %.011.i.i, 1
%exitcond.not.i = icmp eq i64 %116, %umax.i
br i1 %exitcond.not.i, label %.critedge.i.i, label %.preheader.i.i
```
As `%78` is not equal to `%98` in BB `.preheader.preheader.i.i`, we can prove `%101` is non-zero. Then we can simplify the loop exit condition.
Addresses regression introduced by https://github.com/llvm/llvm-project/pull/112742.
>From c34c8f96074deba1aa89a3f0d60583747e557f88 Mon Sep 17 00:00:00 2001
From: Yingwei Zheng <dtcxzyw2333 at gmail.com>
Date: Fri, 18 Oct 2024 12:44:24 +0800
Subject: [PATCH 1/2] [CVP] Add pre-commit tests. NFC.
---
.../CorrelatedValuePropagation/umax.ll | 62 +++++++++++++++++++
1 file changed, 62 insertions(+)
create mode 100644 llvm/test/Transforms/CorrelatedValuePropagation/umax.ll
diff --git a/llvm/test/Transforms/CorrelatedValuePropagation/umax.ll b/llvm/test/Transforms/CorrelatedValuePropagation/umax.ll
new file mode 100644
index 00000000000000..4fbf969c16ca4f
--- /dev/null
+++ b/llvm/test/Transforms/CorrelatedValuePropagation/umax.ll
@@ -0,0 +1,62 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
+; RUN: opt < %s -passes=correlated-propagation -S | FileCheck %s
+
+target datalayout = "p:32:32"
+
+define i32 @infer_range_from_dom_equality(i32 %x, i32 %y) {
+; CHECK-LABEL: define range(i32 1, 0) i32 @infer_range_from_dom_equality(
+; CHECK-SAME: i32 [[X:%.*]], i32 [[Y:%.*]]) {
+; CHECK-NEXT: [[ENTRY:.*:]]
+; CHECK-NEXT: [[COND:%.*]] = icmp eq i32 [[X]], [[Y]]
+; CHECK-NEXT: [[SUB:%.*]] = sub i32 [[X]], [[Y]]
+; CHECK-NEXT: br i1 [[COND]], label %[[IF_THEN:.*]], label %[[IF_ELSE:.*]]
+; CHECK: [[IF_THEN]]:
+; CHECK-NEXT: [[MAX1:%.*]] = call i32 @llvm.umax.i32(i32 [[SUB]], i32 1)
+; CHECK-NEXT: ret i32 [[MAX1]]
+; CHECK: [[IF_ELSE]]:
+; CHECK-NEXT: [[MAX2:%.*]] = call i32 @llvm.umax.i32(i32 [[SUB]], i32 1)
+; CHECK-NEXT: ret i32 [[MAX2]]
+;
+entry:
+ %cond = icmp eq i32 %x, %y
+ %sub = sub i32 %x, %y
+ br i1 %cond, label %if.then, label %if.else
+
+if.then:
+ %max1 = call i32 @llvm.umax.i32(i32 %sub, i32 1)
+ ret i32 %max1
+
+if.else:
+ %max2 = call i32 @llvm.umax.i32(i32 %sub, i32 1)
+ ret i32 %max2
+}
+
+define i32 @infer_range_from_dom_equality_ptrdiff(ptr %x, ptr %y) {
+; CHECK-LABEL: define range(i32 1, 0) i32 @infer_range_from_dom_equality_ptrdiff(
+; CHECK-SAME: ptr [[X:%.*]], ptr [[Y:%.*]]) {
+; CHECK-NEXT: [[COND:%.*]] = icmp eq ptr [[X]], [[Y]]
+; CHECK-NEXT: [[XI:%.*]] = ptrtoint ptr [[X]] to i32
+; CHECK-NEXT: [[YI:%.*]] = ptrtoint ptr [[Y]] to i32
+; CHECK-NEXT: [[SUB:%.*]] = sub i32 [[XI]], [[YI]]
+; CHECK-NEXT: br i1 [[COND]], label %[[IF_THEN:.*]], label %[[IF_ELSE:.*]]
+; CHECK: [[IF_THEN]]:
+; CHECK-NEXT: [[MAX1:%.*]] = call i32 @llvm.umax.i32(i32 [[SUB]], i32 1)
+; CHECK-NEXT: ret i32 [[MAX1]]
+; CHECK: [[IF_ELSE]]:
+; CHECK-NEXT: [[MAX2:%.*]] = call i32 @llvm.umax.i32(i32 [[SUB]], i32 1)
+; CHECK-NEXT: ret i32 [[MAX2]]
+;
+ %cond = icmp eq ptr %x, %y
+ %xi = ptrtoint ptr %x to i32
+ %yi = ptrtoint ptr %y to i32
+ %sub = sub i32 %xi, %yi
+ br i1 %cond, label %if.then, label %if.else
+
+if.then:
+ %max1 = call i32 @llvm.umax.i32(i32 %sub, i32 1)
+ ret i32 %max1
+
+if.else:
+ %max2 = call i32 @llvm.umax.i32(i32 %sub, i32 1)
+ ret i32 %max2
+}
>From cee2b09ed337de5ed9e6b8f90c47372f291831f7 Mon Sep 17 00:00:00 2001
From: Yingwei Zheng <dtcxzyw2333 at gmail.com>
Date: Fri, 18 Oct 2024 12:53:57 +0800
Subject: [PATCH 2/2] [LVI] Infer non-zero from equality icmp
---
llvm/lib/Analysis/LazyValueInfo.cpp | 14 ++++++++++++++
.../Transforms/CorrelatedValuePropagation/umax.ll | 12 ++++--------
2 files changed, 18 insertions(+), 8 deletions(-)
diff --git a/llvm/lib/Analysis/LazyValueInfo.cpp b/llvm/lib/Analysis/LazyValueInfo.cpp
index 10ad4708596cb3..f29777a584772d 100644
--- a/llvm/lib/Analysis/LazyValueInfo.cpp
+++ b/llvm/lib/Analysis/LazyValueInfo.cpp
@@ -1127,6 +1127,20 @@ std::optional<ValueLatticeElement> LazyValueInfoImpl::getValueFromICmpCondition(
if (!Ty->isIntegerTy())
return ValueLatticeElement::getOverdefined();
+ // a - b or ptrtoint(a) - ptrtoint(b) ==/!= 0 if a ==/!= b
+ Value *X, *Y;
+ if (ICI->isEquality() && match(Val, m_Sub(m_Value(X), m_Value(Y)))) {
+ // Peek through ptrtoints
+ match(X, m_PtrToIntSameSize(DL, m_Value(X)));
+ match(Y, m_PtrToIntSameSize(DL, m_Value(Y)));
+ if ((X == LHS && Y == RHS) || (X == RHS && Y == LHS)) {
+ Constant *NullVal = Constant::getNullValue(Val->getType());
+ if (EdgePred == ICmpInst::ICMP_EQ)
+ return ValueLatticeElement::get(NullVal);
+ return ValueLatticeElement::getNot(NullVal);
+ }
+ }
+
unsigned BitWidth = Ty->getScalarSizeInBits();
APInt Offset(BitWidth, 0);
if (matchICmpOperand(Offset, LHS, Val, EdgePred))
diff --git a/llvm/test/Transforms/CorrelatedValuePropagation/umax.ll b/llvm/test/Transforms/CorrelatedValuePropagation/umax.ll
index 4fbf969c16ca4f..5cd615e948adbe 100644
--- a/llvm/test/Transforms/CorrelatedValuePropagation/umax.ll
+++ b/llvm/test/Transforms/CorrelatedValuePropagation/umax.ll
@@ -11,11 +11,9 @@ define i32 @infer_range_from_dom_equality(i32 %x, i32 %y) {
; CHECK-NEXT: [[SUB:%.*]] = sub i32 [[X]], [[Y]]
; CHECK-NEXT: br i1 [[COND]], label %[[IF_THEN:.*]], label %[[IF_ELSE:.*]]
; CHECK: [[IF_THEN]]:
-; CHECK-NEXT: [[MAX1:%.*]] = call i32 @llvm.umax.i32(i32 [[SUB]], i32 1)
-; CHECK-NEXT: ret i32 [[MAX1]]
+; CHECK-NEXT: ret i32 1
; CHECK: [[IF_ELSE]]:
-; CHECK-NEXT: [[MAX2:%.*]] = call i32 @llvm.umax.i32(i32 [[SUB]], i32 1)
-; CHECK-NEXT: ret i32 [[MAX2]]
+; CHECK-NEXT: ret i32 [[SUB]]
;
entry:
%cond = icmp eq i32 %x, %y
@@ -40,11 +38,9 @@ define i32 @infer_range_from_dom_equality_ptrdiff(ptr %x, ptr %y) {
; CHECK-NEXT: [[SUB:%.*]] = sub i32 [[XI]], [[YI]]
; CHECK-NEXT: br i1 [[COND]], label %[[IF_THEN:.*]], label %[[IF_ELSE:.*]]
; CHECK: [[IF_THEN]]:
-; CHECK-NEXT: [[MAX1:%.*]] = call i32 @llvm.umax.i32(i32 [[SUB]], i32 1)
-; CHECK-NEXT: ret i32 [[MAX1]]
+; CHECK-NEXT: ret i32 1
; CHECK: [[IF_ELSE]]:
-; CHECK-NEXT: [[MAX2:%.*]] = call i32 @llvm.umax.i32(i32 [[SUB]], i32 1)
-; CHECK-NEXT: ret i32 [[MAX2]]
+; CHECK-NEXT: ret i32 [[SUB]]
;
%cond = icmp eq ptr %x, %y
%xi = ptrtoint ptr %x to i32
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