[PATCH] D156793: [TailCallElim] Remove the readonly attribute of byval.

[DianQK via Phabricator via llvm-commits]

DianQK created this revision.
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When eliminating a tail call, we modify the values of the arguments.
Therefore, if the byval parameter has a readonly attribute, we have to remove it. It is safe because,
from the perspective of a caller, the byval parameter is always treated as "readonly," even if the readonly attribute is removed.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D156793

Files:
  llvm/lib/Transforms/Scalar/TailRecursionElimination.cpp
  llvm/test/Transforms/TailCallElim/tre-byval-parameter-2.ll
  llvm/test/Transforms/TailCallElim/tre-byval-parameter.ll


Index: llvm/test/Transforms/TailCallElim/tre-byval-parameter.ll
===================================================================
--- llvm/test/Transforms/TailCallElim/tre-byval-parameter.ll
+++ llvm/test/Transforms/TailCallElim/tre-byval-parameter.ll
@@ -25,7 +25,7 @@
 ; Function Attrs: uwtable
 define dso_local i32 @_Z3fooi1S(i32 %count, ptr nocapture readonly byval(%struct.S) align 8 %p1) local_unnamed_addr #0 {
 ; CHECK-LABEL: define {{[^@]+}}@_Z3fooi1S
-; CHECK-SAME: (i32 [[COUNT:%.*]], ptr nocapture readonly byval([[STRUCT_S:%.*]]) align 8 [[P1:%.*]]) local_unnamed_addr #[[ATTR0:[0-9]+]] {
+; CHECK-SAME: (i32 [[COUNT:%.*]], ptr nocapture byval([[STRUCT_S:%.*]]) align 8 [[P1:%.*]]) local_unnamed_addr #[[ATTR0:[0-9]+]] {
 ; CHECK-NEXT:  entry:
 ; CHECK-NEXT:    [[AGG_TMP_I1:%.*]] = alloca [[STRUCT_S]], align 8
 ; CHECK-NEXT:    [[AGG_TMP_I:%.*]] = alloca [[STRUCT_S]], align 8
Index: llvm/test/Transforms/TailCallElim/tre-byval-parameter-2.ll
===================================================================
--- llvm/test/Transforms/TailCallElim/tre-byval-parameter-2.ll
+++ llvm/test/Transforms/TailCallElim/tre-byval-parameter-2.ll
@@ -25,7 +25,7 @@
 ; Function Attrs: noinline nounwind uwtable
 define dso_local void @_Z7dostuff1AS_i(ptr nocapture byval(%struct.A) align 8 %a, ptr nocapture readonly byval(%struct.A) align 8 %b, i32 %i) local_unnamed_addr #0 {
 ; CHECK-LABEL: define {{[^@]+}}@_Z7dostuff1AS_i
-; CHECK-SAME: (ptr nocapture byval([[STRUCT_A:%.*]]) align 8 [[A:%.*]], ptr nocapture readonly byval([[STRUCT_A]]) align 8 [[B:%.*]], i32 [[I:%.*]]) local_unnamed_addr #[[ATTR0:[0-9]+]] {
+; CHECK-SAME: (ptr nocapture byval([[STRUCT_A:%.*]]) align 8 [[A:%.*]], ptr nocapture byval([[STRUCT_A]]) align 8 [[B:%.*]], i32 [[I:%.*]]) local_unnamed_addr #[[ATTR0:[0-9]+]] {
 ; CHECK-NEXT:  entry:
 ; CHECK-NEXT:    [[AGG_TMP52:%.*]] = alloca [[STRUCT_A]], align 8
 ; CHECK-NEXT:    [[AGG_TMP1:%.*]] = alloca [[STRUCT_A]], align 8
Index: llvm/lib/Transforms/Scalar/TailRecursionElimination.cpp
===================================================================
--- llvm/lib/Transforms/Scalar/TailRecursionElimination.cpp
+++ llvm/lib/Transforms/Scalar/TailRecursionElimination.cpp
@@ -675,6 +675,12 @@
   for (unsigned I = 0, E = CI->arg_size(); I != E; ++I) {
     if (CI->isByValArgument(I)) {
       copyLocalTempOfByValueOperandIntoArguments(CI, I);
+      // When eliminating a tail call, we modify the values of the arguments.
+      // Therefore, if the byval parameter has a readonly attribute, we have to
+      // remove it. It is safe because, from the perspective of a caller, the
+      // byval parameter is always treated as "readonly," even if the readonly
+      // attribute is removed.
+      F.removeParamAttr(I, Attribute::ReadOnly);
       ArgumentPHIs[I]->addIncoming(F.getArg(I), BB);
     } else
       ArgumentPHIs[I]->addIncoming(CI->getArgOperand(I), BB);


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