[MemoryLocation] Handle memset_pattern{4,8,16} in getForDest.

[fhahn]

Summary

memset_pattern{4,8,16} writes to the first argument. Use getForDest
to return the corresponding MemoryLocation.

llvm/lib/Analysis/MemoryLocation.cpp

if (const IntrinsicInst *II = dyn_cast<IntrinsicInst>(CB)) {
     case Intrinsic::masked_store:
       return MemoryLocation::getForArgument(CB, 1, TLI);
     }
   }
 
   LibFunc LF;
   if (TLI.getLibFunc(*CB, LF) && TLI.has(LF)) {
     switch (LF) {
+    case LibFunc_memset_pattern4:
+    case LibFunc_memset_pattern8:
+    case LibFunc_memset_pattern16:
     case LibFunc_strncpy:
     case LibFunc_strcpy:
     case LibFunc_strcat:
     case LibFunc_strncat:
       return getForArgument(CB, 0, &TLI);
     default:
       break;
     }

llvm/test/Transforms/DeadStoreElimination/libcalls-darwin.ll

 ; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
 ; RUN: opt -mtriple=x86_64-apple-macosx10.7 -passes=inferattrs,dse -S %s | FileCheck %s
 
 ; Tests for libcalls only available on Darwin platforms.
 
 declare void @memset_pattern4(i8*, i8*, i64)
 declare void @memset_pattern8(i8*, i8*, i64)
 declare void @memset_pattern16(i8*, i8*, i64)
 
 define void @test_memset_pattern4_const_size(i8* noalias %a, i8* noalias %pattern) {
 ; CHECK-LABEL: @test_memset_pattern4_const_size(
 ; CHECK-NEXT:  entry:
-; CHECK-NEXT:    [[A_GEP_1:%.*]] = getelementptr i8, i8* [[A:%.*]], i32 1
-; CHECK-NEXT:    store i8 0, i8* [[A_GEP_1]], align 1
-; CHECK-NEXT:    [[A_GEP_17:%.*]] = getelementptr i8, i8* [[A]], i32 17
+; CHECK-NEXT:    [[A_GEP_17:%.*]] = getelementptr i8, i8* [[A:%.*]], i32 17
 ; CHECK-NEXT:    store i8 1, i8* [[A_GEP_17]], align 1
 ; CHECK-NEXT:    call void @memset_pattern4(i8* [[A]], i8* [[PATTERN:%.*]], i64 17)
 ; CHECK-NEXT:    ret void
 ;
 entry:
   %a.gep.1 = getelementptr i8, i8* %a, i32 1
   store i8 0, i8* %a.gep.1
   %a.gep.17 = getelementptr i8, i8* %a, i32 17
entry:
   store i8 1, i8* %a.gep.17
   call void @memset_pattern4(i8* %a, i8* %pattern, i64 %n)
   ret void
 }
 
 define void @test_memset_pattern8_const_size(i8* noalias %a, i8* noalias %pattern) {
 ; CHECK-LABEL: @test_memset_pattern8_const_size(
 ; CHECK-NEXT:  entry:
-; CHECK-NEXT:    [[A_GEP_1:%.*]] = getelementptr i8, i8* [[A:%.*]], i32 1
-; CHECK-NEXT:    store i8 0, i8* [[A_GEP_1]], align 1
-; CHECK-NEXT:    [[A_GEP_17:%.*]] = getelementptr i8, i8* [[A]], i32 17
+; CHECK-NEXT:    [[A_GEP_17:%.*]] = getelementptr i8, i8* [[A:%.*]], i32 17
 ; CHECK-NEXT:    store i8 1, i8* [[A_GEP_17]], align 1
 ; CHECK-NEXT:    call void @memset_pattern8(i8* [[A]], i8* [[PATTERN:%.*]], i64 17)
 ; CHECK-NEXT:    ret void
 ;
 entry:
   %a.gep.1 = getelementptr i8, i8* %a, i32 1
   store i8 0, i8* %a.gep.1
   %a.gep.17 = getelementptr i8, i8* %a, i32 17
entry:
   store i8 1, i8* %a.gep.17
   call void @memset_pattern8(i8* %a, i8* %pattern, i64 %n)
   ret void
 }
 
 define void @test_memset_pattern16_const_size(i8* noalias %a, i8* noalias %pattern) {
 ; CHECK-LABEL: @test_memset_pattern16_const_size(
 ; CHECK-NEXT:  entry:
-; CHECK-NEXT:    [[A_GEP_1:%.*]] = getelementptr i8, i8* [[A:%.*]], i32 1
-; CHECK-NEXT:    store i8 0, i8* [[A_GEP_1]], align 1
-; CHECK-NEXT:    [[A_GEP_17:%.*]] = getelementptr i8, i8* [[A]], i32 17
+; CHECK-NEXT:    [[A_GEP_17:%.*]] = getelementptr i8, i8* [[A:%.*]], i32 17
 ; CHECK-NEXT:    store i8 1, i8* [[A_GEP_17]], align 1
 ; CHECK-NEXT:    call void @memset_pattern16(i8* [[A]], i8* [[PATTERN:%.*]], i64 17)
 ; CHECK-NEXT:    ret void
 ;
 entry:
   %a.gep.1 = getelementptr i8, i8* %a, i32 1
   store i8 0, i8* %a.gep.1
   %a.gep.17 = getelementptr i8, i8* %a, i32 17