[PATCH] D115829: Allow calls with known writes when trying to remove allocas

[Philip Reames via Phabricator via llvm-commits]

reames updated this revision to Diff 394900.
reames added a comment.

Address review comment about readonly unrelated argument case.


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D115829/new/

https://reviews.llvm.org/D115829

Files:
  llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
  llvm/test/Transforms/InstCombine/trivial-dse-calls.ll


Index: llvm/test/Transforms/InstCombine/trivial-dse-calls.ll
===================================================================
--- llvm/test/Transforms/InstCombine/trivial-dse-calls.ll
+++ llvm/test/Transforms/InstCombine/trivial-dse-calls.ll
@@ -167,4 +167,34 @@
   ret i32 %res
 }
 
+; Show that reading from unrelated memory is okay
+define void @test_unreleated_read() {
+; CHECK-LABEL: @test_unreleated_read(
+; CHECK-NEXT:    ret void
+;
+  %a = alloca i32, align 4
+  %a2 = alloca i32, align 4
+  %bitcast = bitcast i32* %a to i8*
+  %bitcast2 = bitcast i32* %a2 to i8*
+  call void @f2(i8* nocapture writeonly %bitcast, i8* nocapture readonly %bitcast2) argmemonly nounwind willreturn
+  ret void
+}
+
+; But that removing a capture of an unrelated pointer isn't okay.
+define void @test_neg_unreleated_capture() {
+; CHECK-LABEL: @test_neg_unreleated_capture(
+; CHECK-NEXT:    [[A:%.*]] = alloca i32, align 4
+; CHECK-NEXT:    [[A2:%.*]] = alloca i32, align 4
+; CHECK-NEXT:    [[BITCAST:%.*]] = bitcast i32* [[A]] to i8*
+; CHECK-NEXT:    [[BITCAST2:%.*]] = bitcast i32* [[A2]] to i8*
+; CHECK-NEXT:    call void @f2(i8* nocapture nonnull writeonly [[BITCAST]], i8* nonnull readonly [[BITCAST2]]) #[[ATTR1]]
+; CHECK-NEXT:    ret void
+;
+  %a = alloca i32, align 4
+  %a2 = alloca i32, align 4
+  %bitcast = bitcast i32* %a to i8*
+  %bitcast2 = bitcast i32* %a2 to i8*
+  call void @f2(i8* nocapture writeonly %bitcast, i8* readonly %bitcast2) argmemonly nounwind willreturn
+  ret void
+}
 
Index: llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
===================================================================
--- llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
+++ llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
@@ -2577,18 +2577,21 @@
   for (unsigned i = 0; i < CB.arg_size(); i++) {
     if (!CB.getArgOperand(i)->getType()->isPointerTy())
       continue;
-    if (UsedV != CB.getArgOperand(i) && !CB.onlyReadsMemory(i))
-      // A write to another memory location keeps the call live, and thus we
-      // must keep the alloca so that the call has somewhere to write to.
-      // TODO: This results in an inprecision when two values derived from the
-      // same alloca are passed as arguments to the same function.
+    if (!CB.doesNotCapture(i))
+      // capture would allow the address to be read back in an untracked manner
       return false;
+    if (UsedV != CB.getArgOperand(i)) {
+      if (!CB.onlyReadsMemory(i))
+        // A write to another memory location keeps the call live, and thus we
+        // must keep the alloca so that the call has somewhere to write to.
+        // TODO: This results in an inprecision when two values derived from the
+        // same alloca are passed as arguments to the same function.
+        return false;
+      continue;
+    }
     if (!CB.paramHasAttr(i, Attribute::WriteOnly))
       // a read would hold the address live
       return false;
-    if (!CB.doesNotCapture(i))
-      // capture would allow the address to be read back in an untracked manner
-      return false;
   }
   return true;
 }


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