[AssumeBundles] preserve knowledge in DCE

Reviewers: jdoerfert

Reviewed By: jdoerfert

Subscribers: hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D77403

llvm/lib/Transforms/Scalar/DCE.cpp

@@ -25,6 +25,7 @@
 #include "llvm/Pass.h"
 #include "llvm/Support/DebugCounter.h"
 #include "llvm/Transforms/Scalar.h"
+#include "llvm/Transforms/Utils/AssumeBundleBuilder.h"
 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
 #include "llvm/Transforms/Utils/Local.h"
 using namespace llvm;
@@ -127,6 +128,7 @@ static bool DCEInstruction(Instruction *I,
       return false;
 
     salvageDebugInfo(*I);
+    salvageKnowledge(I);
 
     // Null out all of the instruction's operands to see if any operand becomes
     // dead as we go.

llvm/test/Transforms/DCE/basic-preservation.ll

@@ -0,0 +1,11 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt -dce -S --enable-knowledge-retention < %s | FileCheck %s
+
+define void @test(i32* %P) {
+; CHECK-LABEL: @test(
+; CHECK-NEXT:    call void @llvm.assume(i1 true) [ "dereferenceable"(i32* [[P:%.*]], i64 4), "nonnull"(i32* [[P]]) ]
+; CHECK-NEXT:    ret void
+;
+  %a = load i32, i32* %P
+  ret void
+}