Index: llvm/trunk/lib/Target/WebAssembly/WebAssemblyFastISel.cpp
===================================================================
--- llvm/trunk/lib/Target/WebAssembly/WebAssemblyFastISel.cpp
+++ llvm/trunk/lib/Target/WebAssembly/WebAssemblyFastISel.cpp
@@ -63,12 +63,16 @@
   public:
     // Innocuous defaults for our address.
     Address() : Kind(RegBase), Offset(0), GV(0) { Base.Reg = 0; }
-    void setKind(BaseKind K) { Kind = K; }
+    void setKind(BaseKind K) {
+      assert(!isSet() && "Can't change kind with non-zero base");
+      Kind = K;
+    }
     BaseKind getKind() const { return Kind; }
     bool isRegBase() const { return Kind == RegBase; }
     bool isFIBase() const { return Kind == FrameIndexBase; }
     void setReg(unsigned Reg) {
       assert(isRegBase() && "Invalid base register access!");
+      assert(Base.Reg == 0 && "Overwriting non-zero register");
       Base.Reg = Reg;
     }
     unsigned getReg() const {
@@ -77,6 +81,7 @@
     }
     void setFI(unsigned FI) {
       assert(isFIBase() && "Invalid base frame index access!");
+      assert(Base.FI == 0 && "Overwriting non-zero frame index");
       Base.FI = FI;
     }
     unsigned getFI() const {
@@ -91,6 +96,13 @@
     int64_t getOffset() const { return Offset; }
     void setGlobalValue(const GlobalValue *G) { GV = G; }
     const GlobalValue *getGlobalValue() const { return GV; }
+    bool isSet() const {
+      if (isRegBase()) {
+        return Base.Reg != 0;
+      } else {
+        return Base.FI != 0;
+      }
+    }
   };
 
   /// Keep a pointer to the WebAssemblySubtarget around so that we can make the
@@ -297,6 +309,9 @@
     DenseMap<const AllocaInst *, int>::iterator SI =
         FuncInfo.StaticAllocaMap.find(AI);
     if (SI != FuncInfo.StaticAllocaMap.end()) {
+      if (Addr.isSet()) {
+        return false;
+      }
       Addr.setKind(Address::FrameIndexBase);
       Addr.setFI(SI->second);
       return true;
@@ -341,6 +356,9 @@
     break;
   }
   }
+  if (Addr.isSet()) {
+    return false;
+  }
   Addr.setReg(getRegForValue(Obj));
   return Addr.getReg() != 0;
 }
Index: llvm/trunk/test/CodeGen/WebAssembly/offset-fastisel.ll
===================================================================
--- llvm/trunk/test/CodeGen/WebAssembly/offset-fastisel.ll
+++ llvm/trunk/test/CodeGen/WebAssembly/offset-fastisel.ll
@@ -0,0 +1,100 @@
+; RUN: llc < %s -asm-verbose=false -disable-wasm-explicit-locals -fast-isel -fast-isel-abort=1 | FileCheck %s
+
+; TODO: Merge this with offset.ll when fast-isel matches better.
+
+target datalayout = "e-m:e-p:32:32-i64:64-n32:64-S128"
+target triple = "wasm32-unknown-unknown-elf"
+
+; CHECK-LABEL: store_i8_with_variable_gep_offset:
+; CHECK: i32.add    $push[[L0:[0-9]+]]=, $0, $1{{$}}
+; CHECK: i32.const  $push[[L1:[0-9]+]]=, 0{{$}}
+; CHECK: i32.store8 0($pop[[L0]]), $pop[[L1]]{{$}}
+define void @store_i8_with_variable_gep_offset(i8* %p, i32 %idx) {
+  %s = getelementptr inbounds i8, i8* %p, i32 %idx
+  store i8 0, i8* %s
+  ret void
+}
+
+; CHECK-LABEL: store_i8_with_array_alloca_gep:
+; CHECK: i32.const   $push[[L0:[0-9]+]]=, 0{{$}}
+; CHECK: i32.load    $push[[L1:[0-9]+]]=, __stack_pointer($pop[[L0]]){{$}}
+; CHECK: i32.const   $push[[L2:[0-9]+]]=, 32{{$}}
+; CHECK: i32.sub     $push{{[0-9]+}}=, $pop[[L1]], $pop[[L2]]{{$}}
+; CHECK: i32.add     $push[[L4:[0-9]+]]=, $pop{{[0-9]+}}, $0{{$}}
+; CHECK: i32.const   $push[[L5:[0-9]+]]=, 0{{$}}
+; CHECK: i32.store8  0($pop[[L4]]), $pop[[L5]]{{$}}
+define hidden void @store_i8_with_array_alloca_gep(i32 %idx) {
+  %A = alloca [30 x i8], align 16
+  %s = getelementptr inbounds [30 x i8], [30 x i8]* %A, i32 0, i32 %idx
+  store i8 0, i8* %s, align 1
+  ret void
+}
+
+; CHECK-LABEL: store_i32_with_unfolded_gep_offset:
+; CHECK: i32.const $push[[L0:[0-9]+]]=, 24{{$}}
+; CHECK: i32.add   $push[[L1:[0-9]+]]=, $0, $pop[[L0]]{{$}}
+; CHECK: i32.const $push[[L2:[0-9]+]]=, 0{{$}}
+; CHECK: i32.store 0($pop[[L1]]), $pop[[L2]]{{$}}
+define void @store_i32_with_unfolded_gep_offset(i32* %p) {
+  %s = getelementptr i32, i32* %p, i32 6
+  store i32 0, i32* %s
+  ret void
+}
+
+; CHECK-LABEL: store_i32_with_folded_gep_offset:
+; CHECK: i32.store 24($0), $pop{{[0-9]+$}}
+define void @store_i32_with_folded_gep_offset(i32* %p) {
+  %s = getelementptr inbounds i32, i32* %p, i32 6
+  store i32 0, i32* %s
+  ret void
+}
+
+; CHECK-LABEL: load_i32_with_folded_gep_offset:
+; CHECK: i32.load  $push{{[0-9]+}}=, 24($0){{$}}
+define i32 @load_i32_with_folded_gep_offset(i32* %p) {
+  %s = getelementptr inbounds i32, i32* %p, i32 6
+  %t = load i32, i32* %s
+  ret i32 %t
+}
+
+; CHECK-LABEL: store_i64_with_unfolded_gep_offset:
+; CHECK: i32.const $push[[L0:[0-9]+]]=, 24{{$}}
+; CHECK: i32.add   $push[[L1:[0-9]+]]=, $0, $pop[[L0]]{{$}}
+; CHECK: i64.const $push[[L2:[0-9]+]]=, 0{{$}}
+; CHECK: i64.store 0($pop[[L1]]), $pop[[L2]]{{$}}
+define void @store_i64_with_unfolded_gep_offset(i64* %p) {
+  %s = getelementptr i64, i64* %p, i32 3
+  store i64 0, i64* %s
+  ret void
+}
+
+; CHECK-LABEL: store_i8_with_folded_gep_offset:
+; CHECK: i32.store8 24($0), $pop{{[0-9]+$}}
+define void @store_i8_with_folded_gep_offset(i8* %p) {
+  %s = getelementptr inbounds i8, i8* %p, i32 24
+  store i8 0, i8* %s
+  ret void
+}
+
+; CHECK-LABEL: load_i8_u_with_folded_offset:
+; CHECK: i32.load8_u $push{{[0-9]+}}=, 24($0){{$}}
+define i32 @load_i8_u_with_folded_offset(i8* %p) {
+  %q = ptrtoint i8* %p to i32
+  %r = add nuw i32 %q, 24
+  %s = inttoptr i32 %r to i8*
+  %t = load i8, i8* %s
+  %u = zext i8 %t to i32
+  ret i32 %u
+}
+
+; TODO: this should be load8_s, need to fold sign-/zero-extend in fast-isel
+; CHECK-LABEL: load_i8_s_with_folded_offset:
+; CHECK: i32.load8_u $push{{[0-9]+}}=, 24($0){{$}}
+define i32 @load_i8_s_with_folded_offset(i8* %p) {
+  %q = ptrtoint i8* %p to i32
+  %r = add nuw i32 %q, 24
+  %s = inttoptr i32 %r to i8*
+  %t = load i8, i8* %s
+  %u = sext i8 %t to i32
+  ret i32 %u
+}