[SimplifyCFG] Switch to use `paramHasNonNullAttr` #125383

dtcxzyw · 2025-02-02T05:36:26Z

No description provided.

llvm/lib/Transforms/Utils/SimplifyCFG.cpp

…n `Use` (#125519) Address comment #125383 (comment)

…` to work on `Use` (#125519) Address comment llvm/llvm-project#125383 (comment)

…n `Use` (llvm#125519) Address comment llvm#125383 (comment)

nikic

Needs a rebase?

llvmbot · 2025-04-18T14:13:48Z

@llvm/pr-subscribers-llvm-transforms

@llvm/pr-subscribers-llvm-ir

Author: Yingwei Zheng (dtcxzyw)

Changes

Full diff: https://github.com/llvm/llvm-project/pull/125383.diff

3 Files Affected:

(modified) llvm/include/llvm/IR/InstrTypes.h (+10-2)
(modified) llvm/lib/Transforms/Utils/SimplifyCFG.cpp (+2-2)
(modified) llvm/test/Transforms/SimplifyCFG/UnreachableEliminate.ll (+5-6)

diff --git a/llvm/include/llvm/IR/InstrTypes.h b/llvm/include/llvm/IR/InstrTypes.h
index 8e47e3c7b3a7c..61070aa79b15d 100644
--- a/llvm/include/llvm/IR/InstrTypes.h
+++ b/llvm/include/llvm/IR/InstrTypes.h
@@ -1839,7 +1839,11 @@ class CallBase : public Instruction {
   /// Extract the number of dereferenceable bytes for a call or
   /// parameter (0=unknown).
   uint64_t getParamDereferenceableBytes(unsigned i) const {
-    return Attrs.getParamDereferenceableBytes(i);
+    uint64_t Bytes = Attrs.getParamDereferenceableBytes(i);
+    if (const Function *F = getCalledFunction())
+      Bytes =
+          std::max(Bytes, F->getAttributes().getParamDereferenceableBytes(i));
+    return Bytes;
   }
 
   /// Extract the number of dereferenceable_or_null bytes for a call
@@ -1857,7 +1861,11 @@ class CallBase : public Instruction {
   /// Extract the number of dereferenceable_or_null bytes for a
   /// parameter (0=unknown).
   uint64_t getParamDereferenceableOrNullBytes(unsigned i) const {
-    return Attrs.getParamDereferenceableOrNullBytes(i);
+    uint64_t Bytes = Attrs.getParamDereferenceableOrNullBytes(i);
+    if (const Function *F = getCalledFunction())
+      Bytes = std::max(
+          Bytes, F->getAttributes().getParamDereferenceableOrNullBytes(i));
+    return Bytes;
   }
 
   /// Extract a test mask for disallowed floating-point value classes for the
diff --git a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
index 7f53aa7d4f73d..ea171010c7507 100644
--- a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -8214,8 +8214,8 @@ static bool passingValueIsAlwaysUndefined(Value *V, Instruction *I, bool PtrValu
       if (CB->isArgOperand(&Use)) {
         unsigned ArgIdx = CB->getArgOperandNo(&Use);
         // Passing null to a nonnnull+noundef argument is undefined.
-        if (C->isNullValue() && CB->isPassingUndefUB(ArgIdx) &&
-            CB->paramHasAttr(ArgIdx, Attribute::NonNull))
+        if (isa<ConstantPointerNull>(C) &&
+            CB->paramHasNonNullAttr(ArgIdx, /*AllowUndefOrPoison=*/false))
           return !PtrValueMayBeModified;
         // Passing undef to a noundef argument is undefined.
         if (isa<UndefValue>(C) && CB->isPassingUndefUB(ArgIdx))
diff --git a/llvm/test/Transforms/SimplifyCFG/UnreachableEliminate.ll b/llvm/test/Transforms/SimplifyCFG/UnreachableEliminate.ll
index aae1ab032f36e..2da5d18b63f49 100644
--- a/llvm/test/Transforms/SimplifyCFG/UnreachableEliminate.ll
+++ b/llvm/test/Transforms/SimplifyCFG/UnreachableEliminate.ll
@@ -238,7 +238,7 @@ else:
 }
 
 declare ptr @fn_nonnull_noundef_arg(ptr nonnull noundef %p)
-declare ptr @fn_nonnull_deref_arg(ptr nonnull dereferenceable(4) %p)
+declare ptr @fn_deref_arg(ptr dereferenceable(4) %p)
 declare ptr @fn_nonnull_deref_or_null_arg(ptr nonnull dereferenceable_or_null(4) %p)
 declare ptr @fn_nonnull_arg(ptr nonnull %p)
 declare ptr @fn_noundef_arg(ptr noundef %p)
@@ -271,7 +271,7 @@ define void @test9_deref(i1 %X, ptr %Y) {
 ; CHECK-NEXT:  entry:
 ; CHECK-NEXT:    [[TMP0:%.*]] = xor i1 [[X:%.*]], true
 ; CHECK-NEXT:    call void @llvm.assume(i1 [[TMP0]])
-; CHECK-NEXT:    [[TMP1:%.*]] = call ptr @fn_nonnull_deref_arg(ptr [[Y:%.*]])
+; CHECK-NEXT:    [[TMP1:%.*]] = call ptr @fn_deref_arg(ptr [[Y:%.*]])
 ; CHECK-NEXT:    ret void
 ;
 entry:
@@ -282,7 +282,7 @@ if:
 
 else:
   %phi = phi ptr [ %Y, %entry ], [ null, %if ]
-  call ptr @fn_nonnull_deref_arg(ptr %phi)
+  call ptr @fn_deref_arg(ptr %phi)
   ret void
 }
 
@@ -290,9 +290,8 @@ else:
 define void @test9_deref_or_null(i1 %X, ptr %Y) {
 ; CHECK-LABEL: @test9_deref_or_null(
 ; CHECK-NEXT:  entry:
-; CHECK-NEXT:    [[TMP0:%.*]] = xor i1 [[X:%.*]], true
-; CHECK-NEXT:    call void @llvm.assume(i1 [[TMP0]])
-; CHECK-NEXT:    [[TMP1:%.*]] = call ptr @fn_nonnull_deref_or_null_arg(ptr [[Y:%.*]])
+; CHECK-NEXT:    [[Y:%.*]] = select i1 [[X:%.*]], ptr null, ptr [[Y1:%.*]]
+; CHECK-NEXT:    [[TMP1:%.*]] = call ptr @fn_nonnull_deref_or_null_arg(ptr [[Y]])
 ; CHECK-NEXT:    ret void
 ;
 entry:

dtcxzyw · 2025-05-30T14:42:49Z

Ping.

nikic

It looks like this adds some measurable overhead: https://llvm-compile-time-tracker.com/compare.php?from=2a3afa2feb90844ad0f8b0bc57663e2aec06cd0a&to=5b59246712a5c9446a526503818b7f86b824f03c&stat=instructions:u

Can you try changing the check in paramHasNonNullAttr to only use paramHasAttr instead of getParamDereferenceableBytes? This should be a more efficient way to check for non-zero dereferenceable bytes.

asb · 2025-06-03T00:22:35Z

This is causing crashes on bootstrap builds with RVV enabled, with the assertion at the top of paramHasNonNullAttr failing assert(getArgOperand(ArgNo)->getType()->isPointerTy() && "Argument must be a pointer");

To reproduce:

cat - <<'EOF' > crash.ll
$ cat reduced.ll 
target datalayout = "e-m:e-p:64:64-i64:64-i128:128-n32:64-S128"
target triple = "riscv64-unknown-linux-gnu"

define ptr @_ZN4llvm14RegionInfoBaseINS_12RegionTraitsINS_8FunctionEEEEaSEOS4_(ptr %this) {
entry:
  br label %for.body.i.i

for.cond.cleanup.i.i:                             ; preds = %for.body.i.i
  ret ptr null

for.body.i.i:                                     ; preds = %for.body.i.i, %entry
  %P.024.i.i = phi ptr [ %incdec.ptr.i.i, %for.body.i.i ], [ null, %entry ]
  store ptr null, ptr %P.024.i.i, align 8
  %incdec.ptr.i.i = getelementptr i8, ptr %P.024.i.i, i64 16
  %cmp15.not.i.i = icmp eq ptr %P.024.i.i, %this
  br i1 %cmp15.not.i.i, label %for.cond.cleanup.i.i, label %for.body.i.i
}
EOF
/path/to/your/clang -O3 --target=riscv64-linux-gnu -march=rva23u64 crash.ll -fno-crash-diagnostics -mllvm -print-after-all -mllvm -debug

The last IR dump before the crash:

; Function Attrs: nofree norecurse nosync nounwind memory(write, inaccessiblemem: none)
define noalias noundef ptr @_ZN4llvm14RegionInfoBaseINS_12RegionTraitsINS_8FunctionEEEEaSEOS4_(ptr readnone captures(address) %this) local_unnamed_addr #0 {
entry:
  %this1 = ptrtoint ptr %this to i64
  %0 = lshr i64 %this1, 4
  %1 = add nuw nsw i64 %0, 1
  %2 = call i64 @llvm.vscale.i64()
  %3 = shl i64 %2, 1
  %4 = call i64 @llvm.umax.i64(i64 %3, i64 12)
  %min.iters.check = icmp ult i64 %1, %4
  br i1 %min.iters.check, label %scalar.ph, label %vector.scevcheck

vector.scevcheck:                                 ; preds = %entry
  %5 = and i64 %this1, 15
  %ident.check.not = icmp eq i64 %5, 0
  br i1 %ident.check.not, label %vector.ph, label %scalar.ph

vector.ph:                                        ; preds = %vector.scevcheck
  %6 = call i64 @llvm.vscale.i64()
  %7 = shl i64 %6, 1
  %n.mod.vf = urem i64 %1, %7
  %n.vec = sub nsw i64 %1, %n.mod.vf
  %8 = call i64 @llvm.vscale.i64()
  %9 = shl i64 %8, 1
  %10 = shl i64 %n.vec, 4
  %11 = getelementptr i8, ptr null, i64 %10
  br label %vector.body

vector.body:                                      ; preds = %vector.body, %vector.ph
  %index = phi i64 [ 0, %vector.ph ], [ %index.next, %vector.body ]
  %pointer.phi = phi ptr [ null, %vector.ph ], [ %ptr.ind, %vector.body ]
  %12 = shl i64 %8, 5
  %13 = call <vscale x 2 x i64> @llvm.stepvector.nxv2i64()
  %14 = shl <vscale x 2 x i64> %13, splat (i64 4)
  %vector.gep = getelementptr i8, ptr %pointer.phi, <vscale x 2 x i64> %14
  call void @llvm.masked.scatter.nxv2p0.nxv2p0(<vscale x 2 x ptr> zeroinitializer, <vscale x 2 x ptr> %vector.gep, i32 8, <vscale x 2 x i1> splat (i1 true))
  %index.next = add nuw i64 %index, %9
  %ptr.ind = getelementptr i8, ptr %pointer.phi, i64 %12
  %15 = icmp eq i64 %index.next, %n.vec
  br i1 %15, label %middle.block, label %vector.body, !llvm.loop !0

middle.block:                                     ; preds = %vector.body
  %cmp.n = icmp eq i64 %n.mod.vf, 0
  br i1 %cmp.n, label %for.cond.cleanup.i.i, label %scalar.ph

scalar.ph:                                        ; preds = %vector.scevcheck, %entry, %middle.block
  %bc.resume.val = phi ptr [ %11, %middle.block ], [ null, %entry ], [ null, %vector.scevcheck ]
  br label %for.body.i.i

for.cond.cleanup.i.i.loopexit:                    ; preds = %for.body.i.i
  br label %for.cond.cleanup.i.i

for.cond.cleanup.i.i:                             ; preds = %for.cond.cleanup.i.i.loopexit, %middle.block
  ret ptr null

for.body.i.i:                                     ; preds = %scalar.ph, %for.body.i.i
  %P.024.i.i = phi ptr [ %incdec.ptr.i.i, %for.body.i.i ], [ %bc.resume.val, %scalar.ph ]
  store ptr null, ptr %P.024.i.i, align 8
  %incdec.ptr.i.i = getelementptr i8, ptr %P.024.i.i, i64 16
  %cmp15.not.i.i = icmp eq ptr %P.024.i.i, %this
  br i1 %cmp15.not.i.i, label %for.cond.cleanup.i.i.loopexit, label %for.body.i.i, !llvm.loop !3
}

dtcxzyw · 2025-06-03T01:25:30Z

I will have a look.

dtcxzyw requested a review from nikic February 2, 2025 05:36

nikic reviewed Feb 2, 2025

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llvm/lib/Transforms/Utils/SimplifyCFG.cpp Outdated Show resolved Hide resolved

dtcxzyw mentioned this pull request Feb 3, 2025

[NFC][SimplifyCFG] Refactor passingValueIsAlwaysUndefined to work on Use #125519

Merged

dtcxzyw added a commit that referenced this pull request Feb 3, 2025

[NFC][SimplifyCFG] Refactor passingValueIsAlwaysUndefined to work o…

84ba55d

…n `Use` (#125519) Address comment #125383 (comment)

github-actions bot pushed a commit to arm/arm-toolchain that referenced this pull request Feb 3, 2025

Automerge: [NFC][SimplifyCFG] Refactor `passingValueIsAlwaysUndefined…

9cb009a

…` to work on `Use` (#125519) Address comment llvm/llvm-project#125383 (comment)

Icohedron pushed a commit to Icohedron/llvm-project that referenced this pull request Feb 11, 2025

[NFC][SimplifyCFG] Refactor passingValueIsAlwaysUndefined to work o…

c01ad67

…n `Use` (llvm#125519) Address comment llvm#125383 (comment)

nikic reviewed Mar 1, 2025

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dtcxzyw force-pushed the perf/simplifycfg-param-nonnull branch from 7e90465 to 8cdfdae Compare March 1, 2025 14:02

dtcxzyw force-pushed the perf/simplifycfg-param-nonnull branch from 8cdfdae to 244bf1f Compare April 18, 2025 14:13

dtcxzyw marked this pull request as ready for review April 18, 2025 14:13

llvmbot added llvm:ir llvm:transforms labels Apr 18, 2025

[SimplifyCFG] Switch to use paramHasNonNullAttr

5b59246

dtcxzyw force-pushed the perf/simplifycfg-param-nonnull branch from 244bf1f to 5b59246 Compare May 30, 2025 14:42

nikic reviewed May 31, 2025

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[IR] Only check attributes

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nikic approved these changes Jun 1, 2025

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dtcxzyw merged commit 1e08feb into llvm:main Jun 2, 2025
9 of 11 checks passed

dtcxzyw deleted the perf/simplifycfg-param-nonnull branch June 2, 2025 04:20

dtcxzyw mentioned this pull request Jun 3, 2025

[SimplifyCFG] Assertion `getArgOperand(ArgNo)->getType()->isPointerTy() && "Argument must be a pointer"' failed. #142522

Closed

DhruvSrivastavaX pushed a commit to DhruvSrivastavaX/lldb-for-aix that referenced this pull request Jun 12, 2025

[SimplifyCFG] Switch to use paramHasNonNullAttr (llvm#125383)

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