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[IR] Relax convergence requirements on call
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 llvm#134863 and llvm#134844.
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5 files changed

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lines changed

‎llvm/include/llvm/IR/GenericConvergenceVerifierImpl.h

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Original file line numberDiff line numberDiff line change
@@ -102,9 +102,6 @@ void GenericConvergenceVerifier<ContextT>::visit(const InstructionT &I) {
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SeenFirstConvOp = true;
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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/Transforms/ADCE/convergence.ll

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@@ -0,0 +1,92 @@
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; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
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; RUN: opt %s -passes=adce -S | FileCheck %s
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; CHECK: Function Attrs: convergent
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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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; CHECK: Function Attrs: convergent
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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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; CHECK: Function Attrs: convergent
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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) }

‎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: --version 5
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; RUN: opt %s -passes=bdce -S | FileCheck %s
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; CHECK: Function Attrs: convergent
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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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; CHECK: Function Attrs: convergent
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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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; CHECK: Function Attrs: convergent
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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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‎llvm/test/Transforms/FunctionAttrs/convergent.ll

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Original file line numberDiff line numberDiff line change
@@ -129,3 +129,32 @@ define i32 @noopt_friend() convergent {
129129
%a = call i32 @noopt()
130130
ret i32 0
131131
}
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; A function which is stripped of its convergent attribute, even
135+
; if used in a controlled convergence call.
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; This should be OK.
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define i32 @leaf_noconvergent_used() convergent {
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; CHECK: Function Attrs: mustprogress nofree norecurse nosync nounwind willreturn memory(none)
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; 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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;
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ret i32 0
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}
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define i32 @nonleaf_convergent() convergent {
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; 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
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}
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declare token @llvm.experimental.convergence.entry() #1

‎llvm/test/Verifier/convergencectrl-invalid.ll

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Original file line numberDiff line numberDiff line change
@@ -20,7 +20,7 @@ define void @wrong_token() {
2020
ret void
2121
}
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; CHECK: Convergence control token can only be used in a convergent call.
23+
; convergence control token can be used on non-convergent calls, but it has no effect.
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; CHECK-NEXT call void @g(){{.*}}%t05_tok1
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define void @missing.attribute() {
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%t05_tok1 = call token @llvm.experimental.convergence.anchor()

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