From e7ebb87222e33936f6e5f3bd3fda919080ece1a0 Mon Sep 17 00:00:00 2001
From: Philip Reames <listmail@philipreames.com>
Date: Thu, 25 Mar 2021 14:47:31 -0700
Subject: [PATCH] [deref] Handle byval/byref/sret/inalloc/preallocated
 arguments for deref-at-point semantics

All of these are scoped allocations which remain dereferenceable during the lifetime of the callee.

Differential Revision: https://reviews.llvm.org/D99310
---
 llvm/lib/IR/Value.cpp                         |  6 +++++
 .../ValueTracking/memory-dereferenceable.ll   | 24 +++++++++----------
 2 files changed, 18 insertions(+), 12 deletions(-)

diff --git a/llvm/lib/IR/Value.cpp b/llvm/lib/IR/Value.cpp
index 8c06d4fe22d9..fb4eb9a9e3a6 100644
--- a/llvm/lib/IR/Value.cpp
+++ b/llvm/lib/IR/Value.cpp
@@ -739,6 +739,12 @@ static bool canBeFreed(const Value *V) {
   if (isa<Constant>(V))
     return false;
 
+  // Handle byval/byref/sret/inalloca/preallocated arguments.  The storage
+  // lifetime is guaranteed to be longer than the callee's lifetime.
+  if (auto *A = dyn_cast<Argument>(V))
+    if (A->hasPointeeInMemoryValueAttr())
+      return false;
+
   const Function *F = nullptr;
   if (auto *I = dyn_cast<Instruction>(V))
     F = I->getFunction();
diff --git a/llvm/test/Analysis/ValueTracking/memory-dereferenceable.ll b/llvm/test/Analysis/ValueTracking/memory-dereferenceable.ll
index 1b66112db8bb..231fa83417c2 100644
--- a/llvm/test/Analysis/ValueTracking/memory-dereferenceable.ll
+++ b/llvm/test/Analysis/ValueTracking/memory-dereferenceable.ll
@@ -25,8 +25,7 @@ declare i32* @foo()
 
 ; Loads from sret arguments
 ; CHECK-LABEL: 'test_sret'
-; GLOBAL: %sret_gep{{.*}}(aligned)
-; POINT-NOT: %sret_gep{{.*}}(aligned)
+; CHECK: %sret_gep{{.*}}(aligned)
 ; CHECK-NOT: %sret_gep_outside
 define void @test_sret(%struct.A* sret(%struct.A) %result) {
   %sret_gep = getelementptr inbounds %struct.A, %struct.A* %result, i64 0, i32 1, i64 2
@@ -210,22 +209,23 @@ define void @global_allocationsize() {
 
 ; Loads from byval arguments
 ; CHECK-LABEL: 'byval'
-; GLOBAL: %i8_byval{{.*}}(aligned)
-; POINT-NOT: %i8_byval{{.*}}(aligned)
-; CHECK-NOT: %byval_cast
-; GLOBAL: %byval_gep{{.*}}(aligned)
-; POINT-NOT: %byval_gep{{.*}}(aligned)
-; FIXME: Should hold in the point semantics case too
+; CHECK: %i8_byval{{.*}}(aligned)
+; CHECK-NOT: %bad_byval_cast
+; CHECK: %byval_gep{{.*}}(aligned)
+; CHECK: %good_byval_cast{{.*}}(unaligned)
 define void @byval(i8* byval(i8) %i8_byval,
-                        %struct.A* byval(%struct.A) %A_byval) {
+                   %struct.A* byval(%struct.A) %A_byval) {
   call void @mayfree()
-  %i8_byval_load = load i8, i8* %i8_byval
+  load i8, i8* %i8_byval
 
-  %byval_cast = bitcast i8* %i8_byval to i32*
-  %bad_byval_load = load i32, i32* %byval_cast
+  %bad_byval_cast = bitcast i8* %i8_byval to i32*
+  load i32, i32* %bad_byval_cast
 
   %byval_gep = getelementptr inbounds %struct.A, %struct.A* %A_byval, i64 0, i32 1, i64 2
   load i8, i8* %byval_gep
+  %good_byval_cast = bitcast %struct.A* %A_byval to i32*
+  load i32, i32* %good_byval_cast
+
   ret void
 }