[DSE] Allow attribute differences in redundant store elimination

When comparing the instructions, enable attribute intersection to
allow differences in attributes.

Note that we don't actually have to intersect the attributes on
the earlier instruction, because we're not RAUWing, so there's
no chance that we make any values more poisonous.

Author: nikic

llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp

@@ -2210,7 +2210,9 @@ struct DSEState {
 
       Instruction *UpperInst = UpperDef->getMemoryInst();
       auto IsRedundantStore = [&]() {
-        if (DefInst->isIdenticalTo(UpperInst))
+        // We don't care about differences in call attributes here.
+        if (DefInst->isIdenticalToWhenDefined(UpperInst,
+                                              /*IntersectAttrs=*/true))
           return true;
         if (auto *MemSetI = dyn_cast<MemSetInst>(UpperInst)) {
           if (auto *SI = dyn_cast<StoreInst>(DefInst)) {

llvm/test/Transforms/DeadStoreElimination/stores-of-existing-values.ll

@@ -752,7 +752,6 @@ define void @memset_different_attributes_1(i1 %c, ptr %ptr) {
 ; CHECK-NEXT:    call void @llvm.memset.p0.i64(ptr [[PTR:%.*]], i8 0, i64 20, i1 false)
 ; CHECK-NEXT:    br i1 [[C:%.*]], label [[IF:%.*]], label [[END:%.*]]
 ; CHECK:       if:
-; CHECK-NEXT:    call void @llvm.memset.p0.i64(ptr dereferenceable(20) [[PTR]], i8 0, i64 20, i1 false)
 ; CHECK-NEXT:    br label [[END]]
 ; CHECK:       end:
 ; CHECK-NEXT:    ret void
@@ -773,7 +772,6 @@ define void @memset_different_attributes_2(i1 %c, ptr %ptr) {
 ; CHECK-NEXT:    call void @llvm.memset.p0.i64(ptr dereferenceable(20) [[PTR:%.*]], i8 0, i64 20, i1 false)
 ; CHECK-NEXT:    br i1 [[C:%.*]], label [[IF:%.*]], label [[END:%.*]]
 ; CHECK:       if:
-; CHECK-NEXT:    call void @llvm.memset.p0.i64(ptr [[PTR]], i8 0, i64 20, i1 false)
 ; CHECK-NEXT:    br label [[END]]
 ; CHECK:       end:
 ; CHECK-NEXT:    ret void