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[IR] Relax convergence requirements on call (#135794)
Before this commit, having a convergence token on a non-convergent call was considered to be an error. This commit relaxes this requirement and allows convergence tokens to be present on non-convergent calls. When such token is present, they have no effect as the underlying call is non-convergent. This allows passes like DCE to strip `convergent` attribute from functions for which all convergent operations have been stripped. When this happens, a convergence token can still exist in the call-site, causing the verifier to complain. Alternatives have been considered in #134863 and #134844.
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-12
lines changed

6 files changed

+203
-12
lines changed

‎llvm/include/llvm/IR/GenericConvergenceVerifierImpl.h

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@@ -102,9 +102,6 @@ void GenericConvergenceVerifier<ContextT>::visit(const InstructionT &I) {
102102
SeenFirstConvOp = true;
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104104
if (TokenDef || ConvOp != CONV_NONE) {
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Check(isConvergent(I),
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"Convergence control token can only be used in a convergent call.",
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{Context.print(&I)});
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Check(ConvergenceKind != UncontrolledConvergence,
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"Cannot mix controlled and uncontrolled convergence in the same "
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"function.",

‎llvm/test/Assembler/convergence-control.ll

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@@ -24,6 +24,13 @@ define void @mixed2() {
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ret void
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}
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; convergence control token can be used on non-convergent calls,
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; but it has no effect.
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define void @mixed3() {
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%t05_tok1 = call token @llvm.experimental.convergence.anchor()
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call void @g() [ "convergencectrl"(token %t05_tok1) ]
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ret void
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}
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define void @region_nesting1(i1 %arg) convergent {
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A:

‎llvm/test/Transforms/ADCE/convergence.ll

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@@ -0,0 +1,93 @@
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; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --check-globals all --version 5
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; RUN: opt %s -passes=adce -S | FileCheck %s
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define i32 @foo(i32 %a) #0 {
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; CHECK-LABEL: define i32 @foo(
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; CHECK-SAME: i32 [[A:%.*]]) #[[ATTR0:[0-9]+]] {
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; CHECK-NEXT: [[ENTRY:.*:]]
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; CHECK-NEXT: ret i32 [[A]]
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;
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entry:
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%tk = call token @llvm.experimental.convergence.entry()
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ret i32 %a
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}
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define void @bar() #0 {
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; CHECK-LABEL: define void @bar(
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; CHECK-SAME: ) #[[ATTR0]] {
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; CHECK-NEXT: [[ENTRY:.*:]]
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; CHECK-NEXT: ret void
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;
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entry:
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%tk = call token @llvm.experimental.convergence.anchor()
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ret void
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}
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define void @baz() #0 {
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; CHECK-LABEL: define void @baz(
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; CHECK-SAME: ) #[[ATTR0]] {
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; CHECK-NEXT: [[ENTRY:.*:]]
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; CHECK-NEXT: br label %[[HEADER:.*]]
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; CHECK: [[HEADER]]:
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; CHECK-NEXT: br i1 true, label %[[BODY:.*]], label %[[EXIT:.*]]
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; CHECK: [[BODY]]:
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; CHECK-NEXT: br label %[[HEADER]]
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; CHECK: [[EXIT]]:
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; CHECK-NEXT: ret void
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;
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entry:
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%tk0 = call token @llvm.experimental.convergence.entry()
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br label %header
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header:
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%tk1 = call token @llvm.experimental.convergence.loop() [ "convergencectrl"(token %tk0) ]
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br i1 true, label %body, label %exit
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body:
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br label %header
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exit:
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ret void
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}
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define void @indirect_inner() #0 {
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; CHECK-LABEL: define void @indirect_inner(
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; CHECK-SAME: ) #[[ATTR0]] {
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; CHECK-NEXT: [[ENTRY:.*:]]
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; CHECK-NEXT: ret void
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;
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entry:
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%tk0 = call token @llvm.experimental.convergence.entry()
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ret void
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}
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define void @indirect() #0 {
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; CHECK-LABEL: define void @indirect(
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; CHECK-SAME: ) #[[ATTR0]] {
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; CHECK-NEXT: [[ENTRY:.*:]]
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; CHECK-NEXT: [[TK0:%.*]] = call token @llvm.experimental.convergence.entry()
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; CHECK-NEXT: [[VAR:%.*]] = alloca ptr, align 8
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; CHECK-NEXT: store ptr @indirect_inner, ptr [[VAR]], align 8
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; CHECK-NEXT: [[PTR:%.*]] = load ptr, ptr [[VAR]], align 8
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; CHECK-NEXT: call void [[PTR]]() #[[ATTR0]] [ "convergencectrl"(token [[TK0]]) ]
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; CHECK-NEXT: ret void
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;
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entry:
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%tk0 = call token @llvm.experimental.convergence.entry()
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%var = alloca ptr, align 8
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store ptr @indirect_inner, ptr %var, align 8
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%ptr = load ptr, ptr %var, align 8
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call void %ptr() convergent [ "convergencectrl"(token %tk0) ]
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ret void
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}
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declare token @llvm.experimental.convergence.entry() #1
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declare token @llvm.experimental.convergence.anchor() #1
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declare token @llvm.experimental.convergence.loop() #1
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attributes #0 = { convergent }
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attributes #1 = { convergent nocallback nofree nosync nounwind willreturn memory(none) }
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;.
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; CHECK: attributes #[[ATTR0]] = { convergent }
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; CHECK: attributes #[[ATTR1:[0-9]+]] = { convergent nocallback nofree nosync nounwind willreturn memory(none) }
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;.

‎llvm/test/Transforms/BDCE/convergence.ll

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@@ -0,0 +1,62 @@
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; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --check-globals all --version 5
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; RUN: opt %s -passes=bdce -S | FileCheck %s
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define i32 @foo(i32 %a) #0 {
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; CHECK-LABEL: define i32 @foo(
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; CHECK-SAME: i32 [[A:%.*]]) #[[ATTR0:[0-9]+]] {
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; CHECK-NEXT: [[ENTRY:.*:]]
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; CHECK-NEXT: ret i32 [[A]]
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;
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entry:
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%tk0 = call token @llvm.experimental.convergence.entry()
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ret i32 %a
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}
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define void @bar() #0 {
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; CHECK-LABEL: define void @bar(
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; CHECK-SAME: ) #[[ATTR0]] {
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; CHECK-NEXT: [[ENTRY:.*:]]
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; CHECK-NEXT: ret void
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;
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entry:
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%tk0 = call token @llvm.experimental.convergence.anchor()
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ret void
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}
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define void @baz() #0 {
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; CHECK-LABEL: define void @baz(
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; CHECK-SAME: ) #[[ATTR0]] {
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; CHECK-NEXT: [[ENTRY:.*:]]
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; CHECK-NEXT: br label %[[HEADER:.*]]
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; CHECK: [[HEADER]]:
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; CHECK-NEXT: br i1 true, label %[[BODY:.*]], label %[[EXIT:.*]]
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; CHECK: [[BODY]]:
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; CHECK-NEXT: br label %[[HEADER]]
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; CHECK: [[EXIT]]:
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; CHECK-NEXT: ret void
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;
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entry:
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%tk0 = call token @llvm.experimental.convergence.entry()
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br label %header
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header:
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%tk1 = call token @llvm.experimental.convergence.loop() [ "convergencectrl"(token %tk0) ]
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br i1 true, label %body, label %exit
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body:
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br label %header
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exit:
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ret void
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}
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declare token @llvm.experimental.convergence.entry() #1
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declare token @llvm.experimental.convergence.anchor() #1
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declare token @llvm.experimental.convergence.loop() #1
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attributes #0 = { convergent }
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attributes #1 = { convergent nocallback nofree nosync nounwind willreturn memory(none) }
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;.
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; CHECK: attributes #[[ATTR0]] = { convergent }
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; CHECK: attributes #[[ATTR1:[0-9]+]] = { convergent nocallback nofree nosync nounwind willreturn memory(none) }
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;.

‎llvm/test/Transforms/FunctionAttrs/convergent.ll

Lines changed: 41 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -1,4 +1,4 @@
1-
; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --function-signature --check-attributes
1+
; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --function-signature --check-attributes --check-globals
22
; RUN: opt -passes=function-attrs -S < %s | FileCheck %s
33

44
define i32 @nonleaf() convergent {
@@ -129,3 +129,43 @@ define i32 @noopt_friend() convergent {
129129
%a = call i32 @noopt()
130130
ret i32 0
131131
}
132+
133+
134+
; A function which is stripped of its convergent attribute, even
135+
; if used in a controlled convergence call.
136+
; This should be OK.
137+
define i32 @leaf_noconvergent_used() convergent {
138+
; CHECK: Function Attrs: mustprogress nofree norecurse nosync nounwind willreturn memory(none)
139+
; CHECK-LABEL: define {{[^@]+}}@leaf_noconvergent_used
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; CHECK-SAME: () #[[ATTR0]] {
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; CHECK-NEXT: ret i32 0
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;
143+
ret i32 0
144+
}
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146+
define i32 @nonleaf_convergent() convergent {
147+
; CHECK: Function Attrs: convergent mustprogress nofree norecurse nosync nounwind willreturn memory(none)
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; CHECK-LABEL: define {{[^@]+}}@nonleaf_convergent
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; CHECK-SAME: () #[[ATTR7:[0-9]+]] {
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; CHECK-NEXT: [[TMP1:%.*]] = call token @llvm.experimental.convergence.entry()
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; CHECK-NEXT: [[TMP2:%.*]] = call i32 @leaf_noconvergent_used() [ "convergencectrl"(token [[TMP1]]) ]
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; CHECK-NEXT: ret i32 0
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;
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%1 = call token @llvm.experimental.convergence.entry()
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%2 = call i32 @leaf_noconvergent_used() [ "convergencectrl"(token %1) ]
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ret i32 0
157+
}
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declare token @llvm.experimental.convergence.entry() #1
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;.
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; CHECK: attributes #[[ATTR0]] = { mustprogress nofree norecurse nosync nounwind willreturn memory(none) }
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; CHECK: attributes #[[ATTR1]] = { convergent }
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; CHECK: attributes #[[ATTR2]] = { norecurse }
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; CHECK: attributes #[[ATTR3:[0-9]+]] = { convergent nocallback nounwind }
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; CHECK: attributes #[[ATTR4]] = { convergent norecurse nounwind }
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; CHECK: attributes #[[ATTR5]] = { nofree nosync nounwind memory(none) }
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; CHECK: attributes #[[ATTR6]] = { convergent noinline optnone }
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; CHECK: attributes #[[ATTR7]] = { convergent mustprogress nofree norecurse nosync nounwind willreturn memory(none) }
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; CHECK: attributes #[[ATTR8:[0-9]+]] = { convergent nocallback nofree nosync nounwind willreturn memory(none) }
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;.

‎llvm/test/Verifier/convergencectrl-invalid.ll

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Original file line numberDiff line numberDiff line change
@@ -20,14 +20,6 @@ define void @wrong_token() {
2020
ret void
2121
}
2222

23-
; CHECK: Convergence control token can only be used in a convergent call.
24-
; CHECK-NEXT call void @g(){{.*}}%t05_tok1
25-
define void @missing.attribute() {
26-
%t05_tok1 = call token @llvm.experimental.convergence.anchor()
27-
call void @g() [ "convergencectrl"(token %t05_tok1) ]
28-
ret void
29-
}
30-
3123
; CHECK: The 'convergencectrl' bundle requires exactly one token use.
3224
; CHECK-NEXT: call void @g()
3325
define void @multiple_tokens() {

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