[CVP] Infer `nuw`/`nsw` flags for TruncInst #130504

veera-sivarajan · 2025-03-09T18:49:24Z

Proof: https://alive2.llvm.org/ce/z/U-G7yV

Helps: rust-lang/rust#72646 and rust-lang/rust#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.

Fixes #130100

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.

llvmbot · 2025-03-09T18:49:58Z

@llvm/pr-subscribers-clang

@llvm/pr-subscribers-llvm-transforms

Author: Veera (veera-sivarajan)

Changes

Proof: https://alive2.llvm.org/ce/z/U-G7yV

Fixes rust-lang/rust#72646 and rust-lang/rust#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.

Full diff: https://github.com/llvm/llvm-project/pull/130504.diff

6 Files Affected:

(modified) llvm/lib/Transforms/Scalar/CorrelatedValuePropagation.cpp (+31)
(modified) llvm/test/Transforms/CorrelatedValuePropagation/icmp.ll (+1-1)
(modified) llvm/test/Transforms/CorrelatedValuePropagation/range.ll (+2-2)
(modified) llvm/test/Transforms/CorrelatedValuePropagation/sext.ll (+4-4)
(added) llvm/test/Transforms/CorrelatedValuePropagation/trunc.ll (+97)
(modified) llvm/test/Transforms/CorrelatedValuePropagation/zext.ll (+4-4)

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
new file mode 100644
index 0000000000000..ff51a6f8cc64e
--- /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 nuw 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 nsw 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 nuw nsw 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 nuw 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
+}
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

llvm/test/Transforms/CorrelatedValuePropagation/trunc.ll

nikic

Looks like there's a clang test that needs updating.

llvm/test/Transforms/CorrelatedValuePropagation/trunc.ll

dtcxzyw

LGTM. Thank you!

Proof: https://alive2.llvm.org/ce/z/U-G7yV Helps: rust-lang/rust#72646 and rust-lang/rust#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. Fixes llvm#130100

veera-sivarajan added 2 commits March 9, 2025 18:26

Add Test

115fc72

[CVP] Infer nuw/nsw Flags for TruncInst

703460b

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.

veera-sivarajan requested review from dtcxzyw and goldsteinn March 9, 2025 18:49

veera-sivarajan requested a review from nikic as a code owner March 9, 2025 18:49

llvmbot added the llvm:transforms label Mar 9, 2025

nikic mentioned this pull request Mar 9, 2025

Task submission dtcxzyw/llvm-opt-benchmark#1312

Open

dtcxzyw mentioned this pull request Mar 9, 2025

pre-commit: PR130504 dtcxzyw/llvm-opt-benchmark#2199

Open

dtcxzyw linked an issue Mar 10, 2025 that may be closed by this pull request

[CVP] Failure to recognise trunc nsw from assumptions #130100

Closed

dtcxzyw mentioned this pull request Mar 10, 2025

[CVP] Failure to recognise trunc nsw from assumptions #130100

Closed

dtcxzyw reviewed Mar 10, 2025

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llvm/test/Transforms/CorrelatedValuePropagation/trunc.ll Show resolved Hide resolved

Add Test for Assume

c74e9b6

nikic reviewed Mar 10, 2025

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llvm/test/Transforms/CorrelatedValuePropagation/trunc.ll Outdated Show resolved Hide resolved

Update Clang Codegen Test and Remove Unnecessary XORs

bdf2473

llvmbot added the clang Clang issues not falling into any other category label Mar 11, 2025

dtcxzyw mentioned this pull request Mar 12, 2025

Fuzz PR130504 dtcxzyw/llvm-fuzz-service#62

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veera-sivarajan merged commit 5073b5f into llvm:main Mar 12, 2025
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[CVP] Infer `nuw`/`nsw` flags for TruncInst #130504

[CVP] Infer `nuw`/`nsw` flags for TruncInst #130504

veera-sivarajan commented Mar 9, 2025 •

edited by RKSimon

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edited

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[CVP] Infer nuw/nsw flags for TruncInst #130504

[CVP] Infer nuw/nsw flags for TruncInst #130504

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[CVP] Infer `nuw`/`nsw` flags for TruncInst #130504

[CVP] Infer `nuw`/`nsw` flags for TruncInst #130504

veera-sivarajan commented Mar 9, 2025 •

edited by RKSimon

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llvmbot commented Mar 9, 2025 •

edited

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