[EVM] Support OR in conditional jump optimization

* `ISZERO ISZERO OR* PseudoJUMPI` -> `OR* PseudoJUMPI`
* `EQ ISZERO OR* PseudoJUMPI` -> `SUB OR* PseudoJUMPI`
* `SUB ISZERO OR* PseudoJUMPI` -> `EQ OR* PseudoJUMPI`

Author: akiramenai

llvm/lib/Target/EVM/EVMPeephole.cpp

@@ -45,19 +45,18 @@ bool EVMPeephole::runOnMachineFunction(MachineFunction &MF) {
   return Changed;
 }
 
-static bool isNegatadAndJumpedOn(const MachineBasicBlock &MBB,
+static bool isNegatedAndJumpedOn(const MachineBasicBlock &MBB,
                                  MachineBasicBlock::const_iterator I) {
   if (I == MBB.end() || I->getOpcode() != EVM::ISZERO_S)
     return false;
   ++I;
-  if (I == MBB.end())
-    return false;
-  if (I->getOpcode() == EVM::PseudoJUMPI)
-    return true;
-  if (I->getOpcode() != EVM::PUSH4_S)
-    return false;
-  ++I;
-  return I != MBB.end() && I->getOpcode() == EVM::JUMPI;
+  // When a conditional jump’s predicate is a (possibly nested) bitwise `or`,
+  // both operands are eligible for folding. Currently we only fold the operand
+  // computed last.
+  // TODO: #887 Apply folding to all operands.
+  while (I != MBB.end() && I->getOpcode() == EVM::OR_S)
+    ++I;
+  return I != MBB.end() && I->getOpcode() == EVM::PseudoJUMPI;
 }
 
 bool EVMPeephole::optimizeConditionaJumps(MachineBasicBlock &MBB) const {
@@ -67,23 +66,23 @@ bool EVMPeephole::optimizeConditionaJumps(MachineBasicBlock &MBB) const {
   while (I != MBB.end()) {
     // Fold ISZERO ISZERO to nothing, only if it's a predicate to JUMPI.
     if (I->getOpcode() == EVM::ISZERO_S &&
-        isNegatadAndJumpedOn(MBB, std::next(I))) {
+        isNegatedAndJumpedOn(MBB, std::next(I))) {
       std::next(I)->eraseFromParent();
       I->eraseFromParent();
       return true;
     }
 
     // Fold EQ ISZERO to SUB, only if it's a predicate to JUMPI.
     if (I->getOpcode() == EVM::EQ_S &&
-        isNegatadAndJumpedOn(MBB, std::next(I))) {
+        isNegatedAndJumpedOn(MBB, std::next(I))) {
       I->setDesc(TII->get(EVM::SUB_S));
       std::next(I)->eraseFromParent();
       return true;
     }
 
     // Fold SUB ISZERO to EQ, only if it's a predicate to JUMPI.
     if (I->getOpcode() == EVM::SUB_S &&
-        isNegatadAndJumpedOn(MBB, std::next(I))) {
+        isNegatedAndJumpedOn(MBB, std::next(I))) {
       I->setDesc(TII->get(EVM::EQ_S));
       std::next(I)->eraseFromParent();
       return true;

llvm/test/CodeGen/EVM/brcond.ll

@@ -423,3 +423,31 @@ false:
   unreachable
 }
 
+define void @br_or(i256 %a, i256 %b, i256 %c) {
+; CHECK-LABEL: br_or:
+; CHECK:       ; %bb.0:
+; CHECK-NEXT:    JUMPDEST
+; CHECK-NEXT:    SWAP3
+; CHECK-NEXT:    POP
+; CHECK-NEXT:    SWAP1
+; CHECK-NEXT:    DUP3
+; CHECK-NEXT:    SWAP1
+; CHECK-NEXT:    EQ
+; CHECK-NEXT:    ISZERO
+; CHECK-NEXT:    SWAP2
+; CHECK-NEXT:    SUB
+; CHECK-NEXT:    OR
+; CHECK-NEXT:    PUSH4 @.BB20_2
+; CHECK-NEXT:    JUMPI
+; CHECK-NEXT:  ; %bb.1: ; %false
+; CHECK-NEXT:  .BB20_2: ; %true
+; CHECK-NEXT:    JUMPDEST
+  %cond1 = icmp ne i256 %a, %b
+  %cond2 = icmp ne i256 %a, %c
+  %cond = or i1 %cond1, %cond2
+  br i1 %cond, label %true, label %false
+false:
+  unreachable
+true:
+  unreachable
+}