[llvm] [CVP] Infer `nuw`/`nsw` flags for TruncInst (PR #130504)
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llvm-commits at lists.llvm.org
Sun Mar 9 11:49:31 PDT 2025
https://github.com/veera-sivarajan created https://github.com/llvm/llvm-project/pull/130504
Proof: https://alive2.llvm.org/ce/z/U-G7yV
Fixes https://github.com/rust-lang/rust/issues/72646 and https://github.com/rust-lang/rust/issues/122734
Rust compiler's current output: https://godbolt.org/z/7E3fET6Md
IPSCCP can do this transform but it does not help the motivating issue since it runs only once early in the optimization pipeline.
Reimplementing this in CVP folds the motivating issue into a simple `icmp eq` instruction.
>From 115fc72917c279b667fca2cc8dad269ad33bd2bc Mon Sep 17 00:00:00 2001
From: Veera <sveera.2001 at gmail.com>
Date: Sun, 9 Mar 2025 17:44:46 +0000
Subject: [PATCH 1/2] Add Test
---
.../CorrelatedValuePropagation/trunc.ll | 97 +++++++++++++++++++
1 file changed, 97 insertions(+)
create mode 100644 llvm/test/Transforms/CorrelatedValuePropagation/trunc.ll
diff --git a/llvm/test/Transforms/CorrelatedValuePropagation/trunc.ll b/llvm/test/Transforms/CorrelatedValuePropagation/trunc.ll
new file mode 100644
index 0000000000000..27050a0e32dbc
--- /dev/null
+++ b/llvm/test/Transforms/CorrelatedValuePropagation/trunc.ll
@@ -0,0 +1,97 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
+; RUN: opt < %s -passes=correlated-propagation -S | FileCheck %s
+
+
+define i1 @infer_nuw(i8 range(i8 0, 2) %A, i8 range(i8 0, 2) %B) {
+; CHECK-LABEL: define i1 @infer_nuw(
+; CHECK-SAME: i8 range(i8 0, 2) [[A:%.*]], i8 range(i8 0, 2) [[B:%.*]]) {
+; CHECK-NEXT: [[XOR:%.*]] = xor i8 [[B]], [[A]]
+; CHECK-NEXT: [[TRUNC:%.*]] = trunc i8 [[XOR]] to i1
+; CHECK-NEXT: [[RESULT:%.*]] = xor i1 [[TRUNC]], true
+; CHECK-NEXT: ret i1 [[RESULT]]
+;
+ %xor = xor i8 %B, %A
+ %trunc = trunc i8 %xor to i1
+ %result = xor i1 %trunc, true
+ ret i1 %result
+}
+
+
+define i4 @infer_nsw(i8 %A) {
+; CHECK-LABEL: define range(i4 -4, 4) i4 @infer_nsw(
+; CHECK-SAME: i8 [[A:%.*]]) {
+; CHECK-NEXT: [[ASHR:%.*]] = ashr i8 [[A]], 5
+; CHECK-NEXT: [[B:%.*]] = trunc i8 [[ASHR]] to i4
+; CHECK-NEXT: ret i4 [[B]]
+;
+ %ashr = ashr i8 %A, 5
+ %result = trunc i8 %ashr to i4
+ ret i4 %result
+}
+
+
+define i8 @infer_nuw_nsw(i16 range(i16 -5, -3) %A, i16 range(i16 -5, -3) %B) {
+; CHECK-LABEL: define range(i8 0, 8) i8 @infer_nuw_nsw(
+; CHECK-SAME: i16 range(i16 -5, -3) [[A:%.*]], i16 range(i16 -5, -3) [[B:%.*]]) {
+; CHECK-NEXT: [[XOR:%.*]] = xor i16 [[B]], [[A]]
+; CHECK-NEXT: [[TRUNC:%.*]] = trunc i16 [[XOR]] to i8
+; CHECK-NEXT: [[XOR2:%.*]] = xor i8 [[TRUNC]], 1
+; CHECK-NEXT: ret i8 [[XOR2]]
+;
+ %xor = xor i16 %B, %A
+ %trunc = trunc i16 %xor to i8
+ %xor2 = xor i8 %trunc, 1
+ ret i8 %xor2
+}
+
+
+define i1 @rust_issue_122734(i8 range(i8 0, 3) %A, i8 range(i8 0, 3) %B) {
+; CHECK-LABEL: define i1 @rust_issue_122734(
+; CHECK-SAME: i8 range(i8 0, 3) [[A:%.*]], i8 range(i8 0, 3) [[B:%.*]]) {
+; CHECK-NEXT: [[START:.*]]:
+; CHECK-NEXT: [[LHS:%.*]] = icmp eq i8 [[A]], 2
+; CHECK-NEXT: [[RHS:%.*]] = icmp eq i8 [[B]], 2
+; CHECK-NEXT: [[OR:%.*]] = or i1 [[LHS]], [[RHS]]
+; CHECK-NEXT: [[AND:%.*]] = and i1 [[LHS]], [[RHS]]
+; CHECK-NEXT: br i1 [[OR]], label %[[IFTRUE:.*]], label %[[IFFALSE:.*]]
+; CHECK: [[IFTRUE]]:
+; CHECK-NEXT: [[PHI:%.*]] = phi i1 [ [[XOR2:%.*]], %[[IFFALSE]] ], [ [[AND]], %[[START]] ]
+; CHECK-NEXT: ret i1 [[PHI]]
+; CHECK: [[IFFALSE]]:
+; CHECK-NEXT: [[XOR:%.*]] = xor i8 [[A]], [[B]]
+; CHECK-NEXT: [[TRUNC:%.*]] = trunc i8 [[XOR]] to i1
+; CHECK-NEXT: [[XOR2]] = xor i1 [[TRUNC]], true
+; CHECK-NEXT: br label %[[IFTRUE]]
+;
+start:
+ %lhs = icmp eq i8 %A, 2
+ %rhs = icmp eq i8 %B, 2
+ %or = or i1 %lhs, %rhs
+ %and = and i1 %lhs, %rhs
+ br i1 %or, label %iftrue, label %iffalse
+
+iftrue:
+ %phi = phi i1 [ %xor2, %iffalse], [ %and, %start ]
+ ret i1 %phi
+
+iffalse:
+ %xor = xor i8 %A, %B
+ %trunc = trunc i8 %xor to i1
+ %xor2 = xor i1 %trunc, true
+ br label %iftrue
+}
+
+
+define i1 @overdefined_range_negative(i8 %A, i8 %B) {
+; CHECK-LABEL: define i1 @overdefined_range_negative(
+; CHECK-SAME: i8 [[A:%.*]], i8 [[B:%.*]]) {
+; CHECK-NEXT: [[XOR:%.*]] = xor i8 [[A]], [[B]]
+; CHECK-NEXT: [[TRUNC:%.*]] = trunc i8 [[XOR]] to i1
+; CHECK-NEXT: [[XOR2:%.*]] = xor i1 [[TRUNC]], true
+; CHECK-NEXT: ret i1 [[XOR2]]
+;
+ %xor = xor i8 %A, %B
+ %trunc = trunc i8 %xor to i1
+ %xor2 = xor i1 %trunc, true
+ ret i1 %xor2
+}
>From 703460bddfcdbd20ed2ad1d959257b1ebf537097 Mon Sep 17 00:00:00 2001
From: Veera <sveera.2001 at gmail.com>
Date: Sun, 9 Mar 2025 18:21:02 +0000
Subject: [PATCH 2/2] [CVP] Infer `nuw`/`nsw` Flags for TruncInst
IPSCCP can do this transform but it does not help the motivating
issue since it runs only once early in the optimization pipeline.
Reimplementing this in CVP folds the motivating issue into a
simple `icmp eq` instruction.
---
.../Scalar/CorrelatedValuePropagation.cpp | 31 +++++++++++++++++++
.../CorrelatedValuePropagation/icmp.ll | 2 +-
.../CorrelatedValuePropagation/range.ll | 4 +--
.../CorrelatedValuePropagation/sext.ll | 8 ++---
.../CorrelatedValuePropagation/trunc.ll | 8 ++---
.../CorrelatedValuePropagation/zext.ll | 8 ++---
6 files changed, 46 insertions(+), 15 deletions(-)
diff --git a/llvm/lib/Transforms/Scalar/CorrelatedValuePropagation.cpp b/llvm/lib/Transforms/Scalar/CorrelatedValuePropagation.cpp
index 8e74b8645fad9..314a5d15f0f88 100644
--- a/llvm/lib/Transforms/Scalar/CorrelatedValuePropagation.cpp
+++ b/llvm/lib/Transforms/Scalar/CorrelatedValuePropagation.cpp
@@ -1212,6 +1212,34 @@ static bool processAnd(BinaryOperator *BinOp, LazyValueInfo *LVI) {
return true;
}
+static bool processTrunc(TruncInst *TI, LazyValueInfo *LVI) {
+ if (TI->hasNoSignedWrap() && TI->hasNoUnsignedWrap())
+ return false;
+
+ ConstantRange Range =
+ LVI->getConstantRangeAtUse(TI->getOperandUse(0), /*UndefAllowed=*/false);
+ uint64_t DestWidth = TI->getDestTy()->getScalarSizeInBits();
+ bool Changed = false;
+
+ if (!TI->hasNoUnsignedWrap()) {
+ if (Range.getActiveBits() <= DestWidth) {
+ TI->setHasNoUnsignedWrap(true);
+ ++NumNUW;
+ Changed = true;
+ }
+ }
+
+ if (!TI->hasNoSignedWrap()) {
+ if (Range.getMinSignedBits() <= DestWidth) {
+ TI->setHasNoSignedWrap(true);
+ ++NumNSW;
+ Changed = true;
+ }
+ }
+
+ return Changed;
+}
+
static bool runImpl(Function &F, LazyValueInfo *LVI, DominatorTree *DT,
const SimplifyQuery &SQ) {
bool FnChanged = false;
@@ -1275,6 +1303,9 @@ static bool runImpl(Function &F, LazyValueInfo *LVI, DominatorTree *DT,
case Instruction::And:
BBChanged |= processAnd(cast<BinaryOperator>(&II), LVI);
break;
+ case Instruction::Trunc:
+ BBChanged |= processTrunc(cast<TruncInst>(&II), LVI);
+ break;
}
}
diff --git a/llvm/test/Transforms/CorrelatedValuePropagation/icmp.ll b/llvm/test/Transforms/CorrelatedValuePropagation/icmp.ll
index 5fa8f4e1b9f29..7fb1e0718795d 100644
--- a/llvm/test/Transforms/CorrelatedValuePropagation/icmp.ll
+++ b/llvm/test/Transforms/CorrelatedValuePropagation/icmp.ll
@@ -339,7 +339,7 @@ define i1 @test12(i32 %x) {
; CHECK-NEXT: [[ZEXT:%.*]] = zext i32 [[X:%.*]] to i64
; CHECK-NEXT: [[MUL:%.*]] = mul nuw nsw i64 [[ZEXT]], 7
; CHECK-NEXT: [[SHR:%.*]] = lshr i64 [[MUL]], 32
-; CHECK-NEXT: [[TRUNC:%.*]] = trunc i64 [[SHR]] to i32
+; CHECK-NEXT: [[TRUNC:%.*]] = trunc nuw nsw i64 [[SHR]] to i32
; CHECK-NEXT: ret i1 true
;
%zext = zext i32 %x to i64
diff --git a/llvm/test/Transforms/CorrelatedValuePropagation/range.ll b/llvm/test/Transforms/CorrelatedValuePropagation/range.ll
index 03d71fa9b5277..caf1156d79229 100644
--- a/llvm/test/Transforms/CorrelatedValuePropagation/range.ll
+++ b/llvm/test/Transforms/CorrelatedValuePropagation/range.ll
@@ -937,7 +937,7 @@ entry:
define i1 @ctlz_with_range_metadata(i16 %x) {
; CHECK-LABEL: @ctlz_with_range_metadata(
; CHECK-NEXT: [[CTLZ:%.*]] = call i16 @llvm.ctlz.i16(i16 [[X:%.*]], i1 false), !range [[RNG5:![0-9]+]]
-; CHECK-NEXT: [[TRUNC:%.*]] = trunc i16 [[CTLZ]] to i8
+; CHECK-NEXT: [[TRUNC:%.*]] = trunc nuw nsw i16 [[CTLZ]] to i8
; CHECK-NEXT: ret i1 true
;
%ctlz = call i16 @llvm.ctlz.i16(i16 %x, i1 false), !range !{i16 0, i16 8}
@@ -949,7 +949,7 @@ define i1 @ctlz_with_range_metadata(i16 %x) {
define i1 @abs_with_range_metadata(i16 %x) {
; CHECK-LABEL: @abs_with_range_metadata(
; CHECK-NEXT: [[ABS:%.*]] = call i16 @llvm.abs.i16(i16 [[X:%.*]], i1 false), !range [[RNG5]]
-; CHECK-NEXT: [[TRUNC:%.*]] = trunc i16 [[ABS]] to i8
+; CHECK-NEXT: [[TRUNC:%.*]] = trunc nuw nsw i16 [[ABS]] to i8
; CHECK-NEXT: ret i1 true
;
%abs = call i16 @llvm.abs.i16(i16 %x, i1 false), !range !{i16 0, i16 8}
diff --git a/llvm/test/Transforms/CorrelatedValuePropagation/sext.ll b/llvm/test/Transforms/CorrelatedValuePropagation/sext.ll
index 0db520bfc68a2..648ef0864bf17 100644
--- a/llvm/test/Transforms/CorrelatedValuePropagation/sext.ll
+++ b/llvm/test/Transforms/CorrelatedValuePropagation/sext.ll
@@ -20,7 +20,7 @@ define void @test1(i32 %n) {
; CHECK: for.body:
; CHECK-NEXT: [[EXT_WIDE1:%.*]] = zext nneg i32 [[A]] to i64
; CHECK-NEXT: call void @use64(i64 [[EXT_WIDE1]])
-; CHECK-NEXT: [[EXT]] = trunc i64 [[EXT_WIDE1]] to i32
+; CHECK-NEXT: [[EXT]] = trunc nuw nsw i64 [[EXT_WIDE1]] to i32
; CHECK-NEXT: br label [[FOR_COND]]
; CHECK: for.end:
; CHECK-NEXT: ret void
@@ -55,7 +55,7 @@ define void @test2(i32 %n) {
; CHECK: for.body:
; CHECK-NEXT: [[EXT_WIDE:%.*]] = sext i32 [[A]] to i64
; CHECK-NEXT: call void @use64(i64 [[EXT_WIDE]])
-; CHECK-NEXT: [[EXT]] = trunc i64 [[EXT_WIDE]] to i32
+; CHECK-NEXT: [[EXT]] = trunc nsw i64 [[EXT_WIDE]] to i32
; CHECK-NEXT: br label [[FOR_COND]]
; CHECK: for.end:
; CHECK-NEXT: ret void
@@ -87,7 +87,7 @@ define void @test3(i32 %n) {
; CHECK: bb:
; CHECK-NEXT: [[EXT_WIDE1:%.*]] = zext nneg i32 [[N]] to i64
; CHECK-NEXT: call void @use64(i64 [[EXT_WIDE1]])
-; CHECK-NEXT: [[EXT:%.*]] = trunc i64 [[EXT_WIDE1]] to i32
+; CHECK-NEXT: [[EXT:%.*]] = trunc nuw nsw i64 [[EXT_WIDE1]] to i32
; CHECK-NEXT: br label [[EXIT]]
; CHECK: exit:
; CHECK-NEXT: ret void
@@ -115,7 +115,7 @@ define void @test4(i32 %n) {
; CHECK: bb:
; CHECK-NEXT: [[EXT_WIDE:%.*]] = sext i32 [[N]] to i64
; CHECK-NEXT: call void @use64(i64 [[EXT_WIDE]])
-; CHECK-NEXT: [[EXT:%.*]] = trunc i64 [[EXT_WIDE]] to i32
+; CHECK-NEXT: [[EXT:%.*]] = trunc nsw i64 [[EXT_WIDE]] to i32
; CHECK-NEXT: br label [[EXIT]]
; CHECK: exit:
; CHECK-NEXT: ret void
diff --git a/llvm/test/Transforms/CorrelatedValuePropagation/trunc.ll b/llvm/test/Transforms/CorrelatedValuePropagation/trunc.ll
index 27050a0e32dbc..ff51a6f8cc64e 100644
--- a/llvm/test/Transforms/CorrelatedValuePropagation/trunc.ll
+++ b/llvm/test/Transforms/CorrelatedValuePropagation/trunc.ll
@@ -6,7 +6,7 @@ define i1 @infer_nuw(i8 range(i8 0, 2) %A, i8 range(i8 0, 2) %B) {
; CHECK-LABEL: define i1 @infer_nuw(
; CHECK-SAME: i8 range(i8 0, 2) [[A:%.*]], i8 range(i8 0, 2) [[B:%.*]]) {
; CHECK-NEXT: [[XOR:%.*]] = xor i8 [[B]], [[A]]
-; CHECK-NEXT: [[TRUNC:%.*]] = trunc i8 [[XOR]] to i1
+; CHECK-NEXT: [[TRUNC:%.*]] = trunc nuw i8 [[XOR]] to i1
; CHECK-NEXT: [[RESULT:%.*]] = xor i1 [[TRUNC]], true
; CHECK-NEXT: ret i1 [[RESULT]]
;
@@ -21,7 +21,7 @@ define i4 @infer_nsw(i8 %A) {
; CHECK-LABEL: define range(i4 -4, 4) i4 @infer_nsw(
; CHECK-SAME: i8 [[A:%.*]]) {
; CHECK-NEXT: [[ASHR:%.*]] = ashr i8 [[A]], 5
-; CHECK-NEXT: [[B:%.*]] = trunc i8 [[ASHR]] to i4
+; CHECK-NEXT: [[B:%.*]] = trunc nsw i8 [[ASHR]] to i4
; CHECK-NEXT: ret i4 [[B]]
;
%ashr = ashr i8 %A, 5
@@ -34,7 +34,7 @@ define i8 @infer_nuw_nsw(i16 range(i16 -5, -3) %A, i16 range(i16 -5, -3) %B) {
; CHECK-LABEL: define range(i8 0, 8) i8 @infer_nuw_nsw(
; CHECK-SAME: i16 range(i16 -5, -3) [[A:%.*]], i16 range(i16 -5, -3) [[B:%.*]]) {
; CHECK-NEXT: [[XOR:%.*]] = xor i16 [[B]], [[A]]
-; CHECK-NEXT: [[TRUNC:%.*]] = trunc i16 [[XOR]] to i8
+; CHECK-NEXT: [[TRUNC:%.*]] = trunc nuw nsw i16 [[XOR]] to i8
; CHECK-NEXT: [[XOR2:%.*]] = xor i8 [[TRUNC]], 1
; CHECK-NEXT: ret i8 [[XOR2]]
;
@@ -59,7 +59,7 @@ define i1 @rust_issue_122734(i8 range(i8 0, 3) %A, i8 range(i8 0, 3) %B) {
; CHECK-NEXT: ret i1 [[PHI]]
; CHECK: [[IFFALSE]]:
; CHECK-NEXT: [[XOR:%.*]] = xor i8 [[A]], [[B]]
-; CHECK-NEXT: [[TRUNC:%.*]] = trunc i8 [[XOR]] to i1
+; CHECK-NEXT: [[TRUNC:%.*]] = trunc nuw i8 [[XOR]] to i1
; CHECK-NEXT: [[XOR2]] = xor i1 [[TRUNC]], true
; CHECK-NEXT: br label %[[IFTRUE]]
;
diff --git a/llvm/test/Transforms/CorrelatedValuePropagation/zext.ll b/llvm/test/Transforms/CorrelatedValuePropagation/zext.ll
index 44434c696fe37..8e43244a8eb62 100644
--- a/llvm/test/Transforms/CorrelatedValuePropagation/zext.ll
+++ b/llvm/test/Transforms/CorrelatedValuePropagation/zext.ll
@@ -14,7 +14,7 @@ define void @test1(i32 %n) {
; CHECK: for.body:
; CHECK-NEXT: [[EXT_WIDE:%.*]] = zext nneg i32 [[A]] to i64
; CHECK-NEXT: call void @use64(i64 [[EXT_WIDE]])
-; CHECK-NEXT: [[EXT]] = trunc i64 [[EXT_WIDE]] to i32
+; CHECK-NEXT: [[EXT]] = trunc nuw nsw i64 [[EXT_WIDE]] to i32
; CHECK-NEXT: br label [[FOR_COND]]
; CHECK: for.end:
; CHECK-NEXT: ret void
@@ -49,7 +49,7 @@ define void @test2(i32 %n) {
; CHECK: for.body:
; CHECK-NEXT: [[EXT_WIDE:%.*]] = zext i32 [[A]] to i64
; CHECK-NEXT: call void @use64(i64 [[EXT_WIDE]])
-; CHECK-NEXT: [[EXT]] = trunc i64 [[EXT_WIDE]] to i32
+; CHECK-NEXT: [[EXT]] = trunc nuw i64 [[EXT_WIDE]] to i32
; CHECK-NEXT: br label [[FOR_COND]]
; CHECK: for.end:
; CHECK-NEXT: ret void
@@ -81,7 +81,7 @@ define void @test3(i32 %n) {
; CHECK: bb:
; CHECK-NEXT: [[EXT_WIDE:%.*]] = zext nneg i32 [[N]] to i64
; CHECK-NEXT: call void @use64(i64 [[EXT_WIDE]])
-; CHECK-NEXT: [[EXT:%.*]] = trunc i64 [[EXT_WIDE]] to i32
+; CHECK-NEXT: [[EXT:%.*]] = trunc nuw nsw i64 [[EXT_WIDE]] to i32
; CHECK-NEXT: br label [[EXIT]]
; CHECK: exit:
; CHECK-NEXT: ret void
@@ -109,7 +109,7 @@ define void @test4(i32 %n) {
; CHECK: bb:
; CHECK-NEXT: [[EXT_WIDE:%.*]] = zext i32 [[N]] to i64
; CHECK-NEXT: call void @use64(i64 [[EXT_WIDE]])
-; CHECK-NEXT: [[EXT:%.*]] = trunc i64 [[EXT_WIDE]] to i32
+; CHECK-NEXT: [[EXT:%.*]] = trunc nuw i64 [[EXT_WIDE]] to i32
; CHECK-NEXT: br label [[EXIT]]
; CHECK: exit:
; CHECK-NEXT: ret void
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