prefer integer partitions

Author: YonahGoldberg

llvm/lib/Transforms/Scalar/SROA.cpp

@@ -5234,7 +5234,9 @@ AllocaInst *SROA::rewritePartition(AllocaInst &AI, AllocaSlices &AS,
       SliceTy = TypePartitionTy;
 
   // If still not, can we use the largest bitwidth integer type used?
-  if (!SliceTy && CommonUseTy.second)
+  // If SliceTy is a non-promotable aggregate, prefer to represent as an integer type
+  // because it's more likely to be promotable.
+  if ((!SliceTy || !SliceTy->isSingleValueType()) && CommonUseTy.second)
     if (DL.getTypeAllocSize(CommonUseTy.second).getFixedValue() >= P.size()) {
       SliceTy = CommonUseTy.second;
       SliceVecTy = dyn_cast<VectorType>(SliceTy);

llvm/test/Transforms/SROA/prefer-integer-partition.ll

@@ -0,0 +1,17 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt < %s -passes=sroa -S | FileCheck %s
+
+; Ensure that the [2 x half] alloca is spanned by an i32 partition.
+
+define void @test() {
+; CHECK-LABEL: @test(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[TMP0:%.*]] = bitcast i32 42 to float
+; CHECK-NEXT:    ret void
+;
+entry:
+  %alloca = alloca [2 x half]
+  store i32 42, ptr %alloca
+  %val = load float, ptr %alloca
+  ret void
+}