[EVM] Set that gas intrinsic doesn't access storage memory

This will help optimizations that use alias analysis
to search past it, and to optimize further. Benchmark
numbers showed that this is not profitable to do for
heap address space.

Signed-off-by: Vladimir Radosavljevic <[email protected]>

Author: vladimirradosavljevic

llvm/include/llvm/IR/IntrinsicsEVM.td

@@ -108,6 +108,10 @@ def int_evm_msize : Intrinsic<[llvm_i256_ty], [], [IntrWillReturn]>;
 
 def int_evm_pc : Intrinsic<[llvm_i256_ty], [], [IntrWillReturn]>;
 
+// TODO: #904: Set IntrInaccessibleMemOnly attribute to gas intrinsic.
+// Currently, it is not set because benchmark numbers showed that it is not
+// profitable to do that for heap address space. Revisit this decision once
+// optimization for free ptr updates is implemented.
 def int_evm_gas : Intrinsic<[llvm_i256_ty], [], [IntrWillReturn]>;
 
 // Getting values from the context.

llvm/lib/Target/EVM/EVMAliasAnalysis.cpp

@@ -108,6 +108,13 @@ ModRefInfo EVMAAResult::getModRefInfo(const CallBase *Call,
 
   unsigned AS = Loc.Ptr->getType()->getPointerAddressSpace();
   switch (II->getIntrinsicID()) {
+  case Intrinsic::evm_gas:
+    // TODO: #904: Ideally, we would add IntrInaccessibleMemOnly attribute to
+    // gas intrinsic, but benchmark numbers showed that it is not profitable
+    // to do that for heap address space.
+    if (AS == EVMAS::AS_STORAGE || AS == EVMAS::AS_TSTORAGE)
+      return ModRefInfo::NoModRef;
+    return ModRefInfo::ModRef;
   case Intrinsic::evm_return:
   case Intrinsic::evm_staticcall:
     if (AS == EVMAS::AS_STORAGE || AS == EVMAS::AS_TSTORAGE)

llvm/test/CodeGen/EVM/aa-memory-opt.ll

@@ -53,6 +53,8 @@ define i256 @test_different_locsizes() {
   ret i256 %ret
 }
 
+; TODO: #904: It is safe to remove load in this test, but it is not done since benchmark
+; numbers showed that it is not profitable to do that for heap address space.
 define i256 @test_gas_as1() {
 ; CHECK-LABEL: define i256 @test_gas_as1
 ; CHECK-SAME: () local_unnamed_addr #[[ATTR2:[0-9]+]] {
@@ -74,8 +76,7 @@ define i256 @test_gas_as5() {
 ; CHECK-SAME: () local_unnamed_addr #[[ATTR2]] {
 ; CHECK-NEXT:    store i256 2, ptr addrspace(5) inttoptr (i256 2 to ptr addrspace(5)), align 64
 ; CHECK-NEXT:    [[GAS:%.*]] = tail call i256 @llvm.evm.gas()
-; CHECK-NEXT:    [[LOAD:%.*]] = load i256, ptr addrspace(5) inttoptr (i256 2 to ptr addrspace(5)), align 64
-; CHECK-NEXT:    [[RET:%.*]] = add i256 [[LOAD]], [[GAS]]
+; CHECK-NEXT:    [[RET:%.*]] = add i256 [[GAS]], 2
 ; CHECK-NEXT:    ret i256 [[RET]]
 ;
   store i256 2, ptr addrspace(5) inttoptr (i256 2 to ptr addrspace(5)), align 64
@@ -90,8 +91,7 @@ define i256 @test_gas_as6() {
 ; CHECK-SAME: () local_unnamed_addr #[[ATTR2]] {
 ; CHECK-NEXT:    store i256 2, ptr addrspace(6) inttoptr (i256 2 to ptr addrspace(6)), align 64
 ; CHECK-NEXT:    [[GAS:%.*]] = tail call i256 @llvm.evm.gas()
-; CHECK-NEXT:    [[LOAD:%.*]] = load i256, ptr addrspace(6) inttoptr (i256 2 to ptr addrspace(6)), align 64
-; CHECK-NEXT:    [[RET:%.*]] = add i256 [[LOAD]], [[GAS]]
+; CHECK-NEXT:    [[RET:%.*]] = add i256 [[GAS]], 2
 ; CHECK-NEXT:    ret i256 [[RET]]
 ;
   store i256 2, ptr addrspace(6) inttoptr (i256 2 to ptr addrspace(6)), align 64