ART: Transform Sub+Sub into Sub+Add to merge Shl
In the instruction sequence like the following:
t1 = Shl(a, n)
t2 = Sub(t1, *)
r = Sub(*, t2)
Shl cannot be merged with Sub. However it can be done when the first Sub
operands are reordered and the second Sub is replaced with Add:
t1 = Shl(a, n)
t2 = Sub(*, t1)
r = Add(*, t2)
This CL implements this transformation in the ARM/ARM64 instruction simplifiers.
Test: 411-checker-instruct-simplifier-hrem
Test: test.py --host --optimizing --jit --gtest --interpreter
Test: test.py --target --optimizing --jit --interpreter
Test: run-gtests.sh
Change-Id: I24fde29d307f3ad53a8df8bbafe945b4f733ce6c
diff --git a/compiler/optimizing/instruction_simplifier_shared.cc b/compiler/optimizing/instruction_simplifier_shared.cc
index 0f30f66..dc60ba6 100644
--- a/compiler/optimizing/instruction_simplifier_shared.cc
+++ b/compiler/optimizing/instruction_simplifier_shared.cc
@@ -336,4 +336,26 @@
return true;
}
+bool TryReplaceSubSubWithSubAdd(HSub* last_sub) {
+ DCHECK(last_sub->GetRight()->IsSub());
+ HBasicBlock* basic_block = last_sub->GetBlock();
+ ArenaAllocator* allocator = basic_block->GetGraph()->GetAllocator();
+ HInstruction* last_sub_right = last_sub->GetRight();
+ HInstruction* last_sub_left = last_sub->GetLeft();
+ if (last_sub_right->GetUses().HasExactlyOneElement()) {
+ // Reorder operands of last_sub_right: Sub(a, b) -> Sub(b, a).
+ HInstruction* a = last_sub_right->InputAt(0);
+ HInstruction* b = last_sub_right->InputAt(1);
+ last_sub_right->ReplaceInput(b, 0);
+ last_sub_right->ReplaceInput(a, 1);
+
+ // Replace Sub(c, Sub(a, b)) with Add(c, Sub(b, a).
+ HAdd* add = new (allocator) HAdd(last_sub->GetType(), last_sub_left, last_sub_right);
+ basic_block->ReplaceAndRemoveInstructionWith(last_sub, add);
+ return true;
+ } else {
+ return false;
+ }
+}
+
} // namespace art