AsmWriter: Write alloca array size explicitly (and -instcombine fixup)

Write the `alloca` array size explicitly when it's non-canonical.
Previously, if the array size was `iX 1` (where X is not 32), the type
would mutate to `i32` when round-tripping through assembly.

The testcase I added fails in `verify-uselistorder` (as well as
`FileCheck`), since the use-lists for `i32 1` and `i64 1` change.
(Manman Ren came across this when running `verify-uselistorder` on some
non-trivial, optimized code as part of PR5680.)

The type mutation started with r104911, which allowed array sizes to be
something other than an `i32`.  Starting with r204945, we
"canonicalized" to `i64` on 64-bit platforms -- and then on every
round-trip through assembly, mutated back to `i32`.

I bundled a fixup for `-instcombine` to avoid r204945 on scalar
allocations.  (There wasn't a clean way to sequence this into two
commits, since the assembly change on its own caused testcase churn, and
the `-instcombine` change can't be tested without the assembly changes.)

An obvious alternative fix -- change `AllocaInst::AllocaInst()`,
`AsmWriter` and `LLParser` to treat `intptr_t` as the canonical type for
scalar allocations -- was rejected out of hand, since this required
teaching them each about the data layout.

A follow-up commit will add an `-instcombine` to canonicalize the scalar
allocation array size to `i32 1` rather than leaving `iX 1` alone.

rdar://problem/20075773

llvm-svn: 232200

1 files changed, 4 insertions, 4 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp b/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
index b19d2396585..a44a8deda1a 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
@@ -165,6 +165,10 @@ isOnlyCopiedFromConstantGlobal(AllocaInst *AI,
 }
 
 static Instruction *simplifyAllocaArraySize(InstCombiner &IC, AllocaInst &AI) {
+  // Check for array size of 1 (scalar allocation).
+  if (!AI.isArrayAllocation())
+    return nullptr;
+
   // Ensure that the alloca array size argument has type intptr_t, so that
   // any casting is exposed early.
   Type *IntPtrTy = IC.getDataLayout().getIntPtrType(AI.getType());
@@ -174,10 +178,6 @@ static Instruction *simplifyAllocaArraySize(InstCombiner &IC, AllocaInst &AI) {
     return &AI;
   }
 
-  // Check C != 1
-  if (!AI.isArrayAllocation())
-    return nullptr;
-
   // Convert: alloca Ty, C - where C is a constant != 1 into: alloca [C x Ty], 1
   if (const ConstantInt *C = dyn_cast<ConstantInt>(AI.getArraySize())) {
     Type *NewTy = ArrayType::get(AI.getAllocatedType(), C->getZExtValue());