[llvm] e60d62b - Utils: Inhibit load/store folding through phis for llvm.protected.field.ptr.

[via llvm-commits]

Author: Peter Collingbourne
Date: 2025-12-03T17:42:48-08:00
New Revision: e60d62b90f83210f43816fb528e6557ab1770683

URL: https://github.com/llvm/llvm-project/commit/e60d62b90f83210f43816fb528e6557ab1770683
DIFF: https://github.com/llvm/llvm-project/commit/e60d62b90f83210f43816fb528e6557ab1770683.diff

LOG: Utils: Inhibit load/store folding through phis for llvm.protected.field.ptr.

Protected pointer field loads/stores should be paired with the intrinsic
to avoid unnecessary address escapes.

Reviewers: nikic

Reviewed By: nikic

Pull Request: https://github.com/llvm/llvm-project/pull/151649

Added: 
    llvm/test/Transforms/PhaseOrdering/phi-protected-field-ptr.ll

Modified: 
    llvm/lib/Transforms/InstCombine/InstCombinePHI.cpp
    llvm/lib/Transforms/Utils/Local.cpp

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Transforms/InstCombine/InstCombinePHI.cpp b/llvm/lib/Transforms/InstCombine/InstCombinePHI.cpp
index 9815644f5f43d..de97b8e60ac65 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombinePHI.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombinePHI.cpp
@@ -698,8 +698,7 @@ static bool isSafeAndProfitableToSinkLoad(LoadInst *L) {
 Instruction *InstCombinerImpl::foldPHIArgLoadIntoPHI(PHINode &PN) {
   LoadInst *FirstLI = cast<LoadInst>(PN.getIncomingValue(0));
 
-  // Can't forward swifterror through a phi.
-  if (FirstLI->getOperand(0)->isSwiftError())
+  if (!canReplaceOperandWithVariable(FirstLI, 0))
     return nullptr;
 
   // FIXME: This is overconservative; this transform is allowed in some cases
@@ -738,8 +737,7 @@ Instruction *InstCombinerImpl::foldPHIArgLoadIntoPHI(PHINode &PN) {
         LI->getPointerAddressSpace() != LoadAddrSpace)
       return nullptr;
 
-    // Can't forward swifterror through a phi.
-    if (LI->getOperand(0)->isSwiftError())
+    if (!canReplaceOperandWithVariable(LI, 0))
       return nullptr;
 
     // We can't sink the load if the loaded value could be modified between

diff  --git a/llvm/lib/Transforms/Utils/Local.cpp b/llvm/lib/Transforms/Utils/Local.cpp
index a03cf6e953e35..f7842a235b20d 100644
--- a/llvm/lib/Transforms/Utils/Local.cpp
+++ b/llvm/lib/Transforms/Utils/Local.cpp
@@ -3884,6 +3884,12 @@ bool llvm::canReplaceOperandWithVariable(const Instruction *I, unsigned OpIdx) {
   if (Op->isSwiftError())
     return false;
 
+  // Protected pointer field loads/stores should be paired with the intrinsic
+  // to avoid unnecessary address escapes.
+  if (auto *II = dyn_cast<IntrinsicInst>(Op))
+    if (II->getIntrinsicID() == Intrinsic::protected_field_ptr)
+      return false;
+
   // Cannot replace alloca argument with phi/select.
   if (I->isLifetimeStartOrEnd())
     return false;

diff  --git a/llvm/test/Transforms/PhaseOrdering/phi-protected-field-ptr.ll b/llvm/test/Transforms/PhaseOrdering/phi-protected-field-ptr.ll
new file mode 100644
index 0000000000000..bf60de446ea91
--- /dev/null
+++ b/llvm/test/Transforms/PhaseOrdering/phi-protected-field-ptr.ll
@@ -0,0 +1,38 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
+; RUN: opt -O2 -S < %s | FileCheck %s
+
+; Test that no optimization run at -O2 moves the loads into the exit block,
+; as this causes unnecessary address escapes with pointer field protection.
+
+define ptr @phi_prot_ptr(i1 %sel, ptr %p1, ptr %p2) {
+; CHECK-LABEL: define ptr @phi_prot_ptr(
+; CHECK-SAME: i1 [[SEL:%.*]], ptr readonly [[P1:%.*]], ptr readonly [[P2:%.*]]) local_unnamed_addr #[[ATTR0:[0-9]+]] {
+; CHECK-NEXT:    br i1 [[SEL]], label %[[T:.*]], label %[[F:.*]]
+; CHECK:       [[T]]:
+; CHECK-NEXT:    [[PROTP1:%.*]] = tail call ptr @llvm.protected.field.ptr.p0(ptr [[P1]], i64 1, i1 true)
+; CHECK-NEXT:    [[LOAD1:%.*]] = load ptr, ptr [[PROTP1]], align 8
+; CHECK-NEXT:    br label %[[EXIT:.*]]
+; CHECK:       [[F]]:
+; CHECK-NEXT:    [[PROTP2:%.*]] = tail call ptr @llvm.protected.field.ptr.p0(ptr [[P2]], i64 2, i1 true)
+; CHECK-NEXT:    [[LOAD2:%.*]] = load ptr, ptr [[PROTP2]], align 8
+; CHECK-NEXT:    br label %[[EXIT]]
+; CHECK:       [[EXIT]]:
+; CHECK-NEXT:    [[RETVAL:%.*]] = phi ptr [ [[LOAD1]], %[[T]] ], [ [[LOAD2]], %[[F]] ]
+; CHECK-NEXT:    ret ptr [[RETVAL]]
+;
+  br i1 %sel, label %t, label %f
+
+t:
+  %protp1 = call ptr @llvm.protected.field.ptr.p0(ptr %p1, i64 1, i1 true)
+  %load1 = load ptr, ptr %protp1
+  br label %exit
+
+f:
+  %protp2 = call ptr @llvm.protected.field.ptr.p0(ptr %p2, i64 2, i1 true)
+  %load2 = load ptr, ptr %protp2
+  br label %exit
+
+exit:
+  %retval = phi ptr [ %load1, %t ], [ %load2, %f ]
+  ret ptr %retval
+}