[IR] Treat calls with byval ptrs as read-only #122961
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@llvm/pr-subscribers-llvm-analysis @llvm/pr-subscribers-llvm-ir Author: Alex MacLean (AlexMaclean) ChangesFull diff: https://github.com/llvm/llvm-project/pull/122961.diff 5 Files Affected:
diff --git a/llvm/include/llvm/IR/InstrTypes.h b/llvm/include/llvm/IR/InstrTypes.h
index b8d9cc10292f4a..47ddc7555594c5 100644
--- a/llvm/include/llvm/IR/InstrTypes.h
+++ b/llvm/include/llvm/IR/InstrTypes.h
@@ -1719,6 +1719,11 @@ class CallBase : public Instruction {
// FIXME: Once this API is no longer duplicated in `CallSite`, rename this to
// better indicate that this may return a conservative answer.
bool onlyReadsMemory(unsigned OpNo) const {
+ // If the argument is passed byval, the callee does not have access to the
+ // original pointer and thus cannot write to it.
+ if (OpNo < arg_size() && isByValArgument(OpNo))
+ return true;
+
return dataOperandHasImpliedAttr(OpNo, Attribute::ReadOnly) ||
dataOperandHasImpliedAttr(OpNo, Attribute::ReadNone);
}
diff --git a/llvm/lib/Transforms/IPO/FunctionAttrs.cpp b/llvm/lib/Transforms/IPO/FunctionAttrs.cpp
index 06b5d791abe95e..3256e975a846bc 100644
--- a/llvm/lib/Transforms/IPO/FunctionAttrs.cpp
+++ b/llvm/lib/Transforms/IPO/FunctionAttrs.cpp
@@ -890,14 +890,11 @@ determinePointerAccessAttrs(Argument *A,
// can participate in the speculation.
break;
- const bool IsByVal =
- CB.isArgOperand(U) && CB.isByValArgument(CB.getArgOperandNo(U));
-
// The accessors used on call site here do the right thing for calls and
// invokes with operand bundles.
if (CB.doesNotAccessMemory(UseIndex)) {
/* nop */
- } else if (!isModSet(ArgMR) || CB.onlyReadsMemory(UseIndex) || IsByVal) {
+ } else if (!isModSet(ArgMR) || CB.onlyReadsMemory(UseIndex)) {
IsRead = true;
} else if (!isRefSet(ArgMR) ||
CB.dataOperandHasImpliedAttr(UseIndex, Attribute::WriteOnly)) {
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp b/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
index 93d183837d6f43..f87a4a58470402 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
@@ -112,11 +112,6 @@ isOnlyCopiedFromConstantMemory(AAResults *AA, AllocaInst *V,
if ((Call->onlyReadsMemory() && (Call->use_empty() || NoCapture)) ||
(Call->onlyReadsMemory(DataOpNo) && NoCapture))
continue;
-
- // If this is being passed as a byval argument, the caller is making a
- // copy, so it is only a read of the alloca.
- if (IsArgOperand && Call->isByValArgument(DataOpNo))
- continue;
}
// Lifetime intrinsics can be handled by the caller.
diff --git a/llvm/test/Analysis/BasicAA/call-attrs.ll b/llvm/test/Analysis/BasicAA/call-attrs.ll
index c42c908310746d..f6e92dd34ff7fb 100644
--- a/llvm/test/Analysis/BasicAA/call-attrs.ll
+++ b/llvm/test/Analysis/BasicAA/call-attrs.ll
@@ -3,6 +3,7 @@
declare void @readonly_attr(ptr readonly nocapture)
declare void @writeonly_attr(ptr writeonly nocapture)
declare void @readnone_attr(ptr readnone nocapture)
+declare void @byval_attr(ptr byval(i32))
declare void @readonly_func(ptr nocapture) readonly
declare void @writeonly_func(ptr nocapture) writeonly
@@ -24,6 +25,8 @@ entry:
call void @readnone_attr(ptr %p)
call void @readnone_func(ptr %p)
+ call void @byval_attr(ptr %p)
+
call void @read_write(ptr %p, ptr %p, ptr %p)
call void @func() ["deopt" (ptr %p)]
@@ -38,6 +41,7 @@ entry:
; CHECK: Just Mod: Ptr: i8* %p <-> call void @writeonly_func(ptr %p)
; CHECK: NoModRef: Ptr: i8* %p <-> call void @readnone_attr(ptr %p)
; CHECK: NoModRef: Ptr: i8* %p <-> call void @readnone_func(ptr %p)
+; CHECK: Just Ref: Ptr: i8* %p <-> call void @byval_attr(ptr %p)
; CHECK: Both ModRef: Ptr: i8* %p <-> call void @read_write(ptr %p, ptr %p, ptr %p)
; CHECK: Just Ref: Ptr: i8* %p <-> call void @func() [ "deopt"(ptr %p) ]
; CHECK: Both ModRef: Ptr: i8* %p <-> call void @writeonly_attr(ptr %p) [ "deopt"(ptr %p) ]
diff --git a/llvm/test/Transforms/SROA/readonlynocapture.ll b/llvm/test/Transforms/SROA/readonlynocapture.ll
index 2c21624f3ea51a..611c90ac32b5a2 100644
--- a/llvm/test/Transforms/SROA/readonlynocapture.ll
+++ b/llvm/test/Transforms/SROA/readonlynocapture.ll
@@ -390,4 +390,20 @@ define i32 @testcallalloca() {
ret i32 %l1
}
+declare void @callee_byval(ptr byval(i32) %p)
+
+define i32 @simple_byval() {
+; CHECK-LABEL: @simple_byval(
+; CHECK-NEXT: [[A:%.*]] = alloca i32, align 4
+; CHECK-NEXT: store i32 0, ptr [[A]], align 4
+; CHECK-NEXT: call void @callee_byval(ptr [[A]])
+; CHECK-NEXT: ret i32 0
+;
+ %a = alloca i32
+ store i32 0, ptr %a
+ call void @callee_byval(ptr %a)
+ %l1 = load i32, ptr %a
+ ret i32 %l1
+}
+
declare void @llvm.memcpy.p0.p0.i64(ptr, ptr, i64, i1)
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LLVM Buildbot has detected a new failure on builder Full details are available at: https://lab.llvm.org/buildbot/#/builders/153/builds/19858 Here is the relevant piece of the build log for the reference |
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