[IR] Fix mayReadFromMemory() for writeonly calls

Yevgeny Rouban · Yevgeny Rouban · commit 5e5af533ab16 · 2019-10-21T06:52:08.000Z
Current implementation of Instruction::mayReadFromMemory() returns !doesNotAccessMemory() which is !ReadNone. This does not take into account that the writeonly attribute also indicates that the call does not read from memory. The patch changes the predicate to !doesNotReadMemory() that reflects the intended behavior. Differential Revision: https://reviews.llvm.org/D69086 llvm-svn: 375389
diff --git a/llvm/lib/IR/Instruction.cpp b/llvm/lib/IR/Instruction.cpp
@@ -524,7 +524,7 @@ bool Instruction::mayReadFromMemory() const {
   case Instruction::Call:
   case Instruction::Invoke:
   case Instruction::CallBr:
-    return !cast<CallBase>(this)->doesNotAccessMemory();
+    return !cast<CallBase>(this)->doesNotReadMemory();
   case Instruction::Store:
     return !cast<StoreInst>(this)->isUnordered();
   }
diff --git a/llvm/test/CodeGen/AMDGPU/llvm.amdgcn.ds.gws.init.ll b/llvm/test/CodeGen/AMDGPU/llvm.amdgcn.ds.gws.init.ll
@@ -114,7 +114,7 @@ define amdgpu_kernel void @gws_init_vgpr_offset_add(i32 %val) #0 {
 ; LOOP: s_mov_b32 m0, -1
 ; LOOP: ds_write_b32
 define amdgpu_kernel void @gws_init_save_m0_init_constant_offset(i32 %val) #0 {
-  store i32 1, i32 addrspace(3)* @lds
+  store volatile i32 1, i32 addrspace(3)* @lds
   call void @llvm.amdgcn.ds.gws.init(i32 %val, i32 10)
   store i32 2, i32 addrspace(3)* @lds
   ret void
diff --git a/llvm/test/Transforms/EarlyCSE/writeonly.ll b/llvm/test/Transforms/EarlyCSE/writeonly.ll
@@ -0,0 +1,15 @@
+; RUN: opt -S -early-cse < %s | FileCheck %s
+
+@var = global i32 undef
+declare void @foo() nounwind
+
+define void @test() {
+; CHECK-LABEL: @test(
+; CHECK-NOT: store
+  store i32 1, i32* @var
+; CHECK: call void @foo()
+  call void @foo() writeonly
+; CHECK: store i32 2, i32* @var
+  store i32 2, i32* @var
+  ret void
+}

Original file line number	Diff line number	Diff line change
`@@ -524,7 +524,7 @@ bool Instruction::mayReadFromMemory() const {`
`524`	`524`	`case Instruction::Call:`
`525`	`525`	`case Instruction::Invoke:`
`526`	`526`	`case Instruction::CallBr:`
`527`		`- return !cast<CallBase>(this)->doesNotAccessMemory();`
	`527`	`+ return !cast<CallBase>(this)->doesNotReadMemory();`
`528`	`528`	`case Instruction::Store:`
`529`	`529`	`return !cast<StoreInst>(this)->isUnordered();`
`530`	`530`	`}`