[llvm] [IR] Return correct memory effects for `convergencectrl` (PR #129874)

[Yingwei Zheng via llvm-commits]

https://github.com/dtcxzyw created https://github.com/llvm/llvm-project/pull/129874

`convergencectrl` doesn't imply any memory access.
Closes https://github.com/llvm/llvm-project/issues/129856.


>From 0bfbdbb5c5acc3419e745cd1cfe482c90671684d Mon Sep 17 00:00:00 2001
From: Yingwei Zheng <dtcxzyw2333 at gmail.com>
Date: Wed, 5 Mar 2025 19:25:54 +0800
Subject: [PATCH 1/3] [DCE] Add pre-commit tests. NFC.

---
 llvm/test/Transforms/DCE/op_bundles.ll | 14 ++++++++++++++
 1 file changed, 14 insertions(+)
 create mode 100644 llvm/test/Transforms/DCE/op_bundles.ll

diff --git a/llvm/test/Transforms/DCE/op_bundles.ll b/llvm/test/Transforms/DCE/op_bundles.ll
new file mode 100644
index 0000000000000..e6ff49512231f
--- /dev/null
+++ b/llvm/test/Transforms/DCE/op_bundles.ll
@@ -0,0 +1,14 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
+; RUN: opt -S < %s -passes=dce  | FileCheck %s
+
+define void @dead_readfirstlane_convergencetoken(<2 x i32> %src) convergent {
+; CHECK-LABEL: define void @dead_readfirstlane_convergencetoken(
+; CHECK-SAME: <2 x i32> [[SRC:%.*]]) #[[ATTR0:[0-9]+]] {
+; CHECK-NEXT:    [[T:%.*]] = tail call token @llvm.experimental.convergence.entry()
+; CHECK-NEXT:    [[VEC:%.*]] = call <2 x i32> @llvm.amdgcn.readfirstlane.v2i32(<2 x i32> [[SRC]]) [ "convergencectrl"(token [[T]]) ]
+; CHECK-NEXT:    ret void
+;
+  %t = tail call token @llvm.experimental.convergence.entry()
+  %vec = call <2 x i32> @llvm.amdgcn.readfirstlane.v2i32(<2 x i32> %src) [ "convergencectrl"(token %t) ]
+  ret void
+}

>From a88458c36aabff769978e331502689f23e7d4190 Mon Sep 17 00:00:00 2001
From: Yingwei Zheng <dtcxzyw2333 at gmail.com>
Date: Wed, 5 Mar 2025 19:30:09 +0800
Subject: [PATCH 2/3] [IR] Return correct memory effects for convergencectrl

---
 llvm/lib/IR/Instructions.cpp           | 8 +++++---
 llvm/test/Transforms/DCE/op_bundles.ll | 2 --
 2 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/llvm/lib/IR/Instructions.cpp b/llvm/lib/IR/Instructions.cpp
index b5d1bc81b9d95..d2cf0ae2c1778 100644
--- a/llvm/lib/IR/Instructions.cpp
+++ b/llvm/lib/IR/Instructions.cpp
@@ -609,15 +609,17 @@ bool CallBase::hasReadingOperandBundles() const {
   // Implementation note: this is a conservative implementation of operand
   // bundle semantics, where *any* non-assume operand bundle (other than
   // ptrauth) forces a callsite to be at least readonly.
-  return hasOperandBundlesOtherThan(
-             {LLVMContext::OB_ptrauth, LLVMContext::OB_kcfi}) &&
+  return hasOperandBundlesOtherThan({LLVMContext::OB_ptrauth,
+                                     LLVMContext::OB_kcfi,
+                                     LLVMContext::OB_convergencectrl}) &&
          getIntrinsicID() != Intrinsic::assume;
 }
 
 bool CallBase::hasClobberingOperandBundles() const {
   return hasOperandBundlesOtherThan(
              {LLVMContext::OB_deopt, LLVMContext::OB_funclet,
-              LLVMContext::OB_ptrauth, LLVMContext::OB_kcfi}) &&
+              LLVMContext::OB_ptrauth, LLVMContext::OB_kcfi,
+              LLVMContext::OB_convergencectrl}) &&
          getIntrinsicID() != Intrinsic::assume;
 }
 
diff --git a/llvm/test/Transforms/DCE/op_bundles.ll b/llvm/test/Transforms/DCE/op_bundles.ll
index e6ff49512231f..0d3b4db8265e8 100644
--- a/llvm/test/Transforms/DCE/op_bundles.ll
+++ b/llvm/test/Transforms/DCE/op_bundles.ll
@@ -4,8 +4,6 @@
 define void @dead_readfirstlane_convergencetoken(<2 x i32> %src) convergent {
 ; CHECK-LABEL: define void @dead_readfirstlane_convergencetoken(
 ; CHECK-SAME: <2 x i32> [[SRC:%.*]]) #[[ATTR0:[0-9]+]] {
-; CHECK-NEXT:    [[T:%.*]] = tail call token @llvm.experimental.convergence.entry()
-; CHECK-NEXT:    [[VEC:%.*]] = call <2 x i32> @llvm.amdgcn.readfirstlane.v2i32(<2 x i32> [[SRC]]) [ "convergencectrl"(token [[T]]) ]
 ; CHECK-NEXT:    ret void
 ;
   %t = tail call token @llvm.experimental.convergence.entry()

>From a4744bfc51eb387f062a17c2cfcdf39743d869b2 Mon Sep 17 00:00:00 2001
From: Yingwei Zheng <dtcxzyw2333 at gmail.com>
Date: Wed, 5 Mar 2025 19:45:02 +0800
Subject: [PATCH 3/3] [IRNormalizer] Fix test failure.

---
 .../IRNormalizer/regression-convergence-tokens.ll         | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/llvm/test/Transforms/IRNormalizer/regression-convergence-tokens.ll b/llvm/test/Transforms/IRNormalizer/regression-convergence-tokens.ll
index 633cf091da508..88eff971b9576 100644
--- a/llvm/test/Transforms/IRNormalizer/regression-convergence-tokens.ll
+++ b/llvm/test/Transforms/IRNormalizer/regression-convergence-tokens.ll
@@ -7,14 +7,14 @@ define i32 @nested(i32 %src) #0 {
 ; CHECK-SAME: i32 [[A0:%.*]]) #[[ATTR0:[0-9]+]] {
 ; CHECK-NEXT:  [[BB15160:.*:]]
 ; CHECK-NEXT:    [[T1:%.*]] = call token @llvm.experimental.convergence.entry()
-; CHECK-NEXT:    %"vl15001llvm.experimental.convergence.anchor()" = call token @llvm.experimental.convergence.anchor()
-; CHECK-NEXT:    %"op68297llvm.amdgcn.readfirstlane.i32([[A0]], vl15001llvm.experimental.convergence.anchor())" = call i32 @llvm.amdgcn.readfirstlane.i32(i32 [[A0]]) [ "convergencectrl"(token %"vl15001llvm.experimental.convergence.anchor()") ]
-; CHECK-NEXT:    ret i32 undef
+; CHECK-NEXT:    %"vl77672llvm.experimental.convergence.anchor()" = call token @llvm.experimental.convergence.anchor()
+; CHECK-NEXT:    %"op68297(vl77672)" = call i32 @llvm.amdgcn.readfirstlane.i32(i32 [[A0]]) [ "convergencectrl"(token %"vl77672llvm.experimental.convergence.anchor()") ]
+; CHECK-NEXT:    ret i32 %"op68297(vl77672)"
 ;
   %t1 = call token @llvm.experimental.convergence.entry()
   %t2 = call token @llvm.experimental.convergence.anchor()
   %r2 = call i32 @llvm.amdgcn.readfirstlane(i32 %src) [ "convergencectrl"(token %t2) ]
-  ret i32 undef
+  ret i32 %r2
 }
 
 ; Function Attrs: convergent nounwind readnone