[llvm][Mips] Bail on underaligned loads/stores in FastISel.

Author: alexrp

llvm/lib/Target/Mips/MipsFastISel.cpp

@@ -881,38 +881,50 @@ bool MipsFastISel::selectLogicalOp(const Instruction *I) {
 }
 
 bool MipsFastISel::selectLoad(const Instruction *I) {
+  const LoadInst *LI = cast<LoadInst>(I);
+
   // Atomic loads need special handling.
-  if (cast<LoadInst>(I)->isAtomic())
+  if (LI->isAtomic())
     return false;
 
   // Verify we have a legal type before going any further.
   MVT VT;
-  if (!isLoadTypeLegal(I->getType(), VT))
+  if (!isLoadTypeLegal(LI->getType(), VT))
+    return false;
+
+  // Underaligned loads need special handling.
+  if (LI->getAlign() < VT.getFixedSizeInBits() / 8)
     return false;
 
   // See if we can handle this address.
   Address Addr;
-  if (!computeAddress(I->getOperand(0), Addr))
+  if (!computeAddress(LI->getOperand(0), Addr))
     return false;
 
   unsigned ResultReg;
   if (!emitLoad(VT, ResultReg, Addr))
     return false;
-  updateValueMap(I, ResultReg);
+  updateValueMap(LI, ResultReg);
   return true;
 }
 
 bool MipsFastISel::selectStore(const Instruction *I) {
-  Value *Op0 = I->getOperand(0);
+  const StoreInst *SI = cast<StoreInst>(I);
+
+  Value *Op0 = SI->getOperand(0);
   unsigned SrcReg = 0;
 
   // Atomic stores need special handling.
-  if (cast<StoreInst>(I)->isAtomic())
+  if (SI->isAtomic())
     return false;
 
   // Verify we have a legal type before going any further.
   MVT VT;
-  if (!isLoadTypeLegal(I->getOperand(0)->getType(), VT))
+  if (!isLoadTypeLegal(SI->getOperand(0)->getType(), VT))
+    return false;
+
+  // Underaligned stores need special handling.
+  if (SI->getAlign() < VT.getFixedSizeInBits() / 8)
     return false;
 
   // Get the value to be stored into a register.
@@ -922,7 +934,7 @@ bool MipsFastISel::selectStore(const Instruction *I) {
 
   // See if we can handle this address.
   Address Addr;
-  if (!computeAddress(I->getOperand(1), Addr))
+  if (!computeAddress(SI->getOperand(1), Addr))
     return false;
 
   if (!emitStore(VT, SrcReg, Addr))

llvm/test/CodeGen/Mips/Fast-ISel/underaligned-load-store.ll

@@ -0,0 +1,17 @@
+; RUN: llc < %s -march mips -fast-isel -relocation-model pic | FileCheck %s -check-prefixes=MIPS
+
+@var = external global i32, align 1
+
+; FastISel should bail on the underaligned load and store.
+define dso_local ccc i32 @__start() {
+; MIPS:      lw  $1, %got(var)($1)
+; MIPS-NEXT: lwl $2, 0($1)
+; MIPS-NEXT: lwr $2, 3($1)
+    %1 = load i32, ptr @var, align 1
+; MIPS:      addiu $3, $zero, 42
+; MIPS-NEXT: swl $3, 0($1)
+; MIPS-NEXT: jr $ra
+; MIPS-NEXT: swr $3, 3($1)
+    store i32 42, ptr @var, align 1
+    ret i32 %1
+}