SROA: Only split loads on byte boundaries

r199771 accidently broke the logic that makes sure that SROA only splits
load on byte boundaries.  If such a split happens, some bits get lost
when reassembling loads of wider types, causing data corruption.

Move the width check up to reject such splits early, avoiding the
corruption.  Fixes PR19250.

Patch by: Björn Steinbrink <[email protected]>

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@211082 91177308-0d34-0410-b5e6-96231b3b80d8

Author: dexonsmith

lib/Transforms/Scalar/SROA.cpp

@@ -1032,11 +1032,6 @@ static Type *findCommonType(AllocaSlices::const_iterator B,
       UserTy = SI->getValueOperand()->getType();
     }
 
-    if (!UserTy || (Ty && Ty != UserTy))
-      TyIsCommon = false; // Give up on anything but an iN type.
-    else
-      Ty = UserTy;
-
     if (IntegerType *UserITy = dyn_cast_or_null<IntegerType>(UserTy)) {
       // If the type is larger than the partition, skip it. We only encounter
       // this for split integer operations where we want to use the type of the
@@ -1051,6 +1046,13 @@ static Type *findCommonType(AllocaSlices::const_iterator B,
       if (!ITy || ITy->getBitWidth() < UserITy->getBitWidth())
         ITy = UserITy;
     }
+
+    // To avoid depending on the order of slices, Ty and TyIsCommon must not
+    // depend on types skipped above.
+    if (!UserTy || (Ty && Ty != UserTy))
+      TyIsCommon = false; // Give up on anything but an iN type.
+    else
+      Ty = UserTy;
   }
 
   return TyIsCommon ? Ty : ITy;

test/Transforms/SROA/slice-order-independence.ll

@@ -0,0 +1,37 @@
+; RUN: opt < %s -sroa -S | FileCheck %s
+target datalayout = "e-p:64:64:64-p1:16:16:16-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:32:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-n8:16:32:64"
+
+declare void @llvm.memcpy.p0i8.p0i8.i32(i8* nocapture, i8* nocapture, i32, i32, i1) nounwind
+
+; Check that the chosen type for a split is independent from the order of
+; slices even in case of types that are skipped because their width is not a
+; byte width multiple
+define void @skipped_inttype_first({ i16*, i32 }*) {
+; CHECK-LABEL: @skipped_inttype_first
+; CHECK: alloca i8*
+  %arg = alloca { i16*, i32 }, align 8
+  %2 = bitcast { i16*, i32 }* %0 to i8*
+  %3 = bitcast { i16*, i32 }* %arg to i8*
+  call void @llvm.memcpy.p0i8.p0i8.i32(i8* %3, i8* %2, i32 16, i32 8, i1 false)
+  %b = getelementptr inbounds { i16*, i32 }* %arg, i64 0, i32 0
+  %pb0 = bitcast i16** %b to i63*
+  %b0 = load i63* %pb0
+  %pb1 = bitcast i16** %b to i8**
+  %b1 = load i8** %pb1
+  ret void
+}
+
+define void @skipped_inttype_last({ i16*, i32 }*) {
+; CHECK-LABEL: @skipped_inttype_last
+; CHECK: alloca i8*
+  %arg = alloca { i16*, i32 }, align 8
+  %2 = bitcast { i16*, i32 }* %0 to i8*
+  %3 = bitcast { i16*, i32 }* %arg to i8*
+  call void @llvm.memcpy.p0i8.p0i8.i32(i8* %3, i8* %2, i32 16, i32 8, i1 false)
+  %b = getelementptr inbounds { i16*, i32 }* %arg, i64 0, i32 0
+  %pb1 = bitcast i16** %b to i8**
+  %b1 = load i8** %pb1
+  %pb0 = bitcast i16** %b to i63*
+  %b0 = load i63* %pb0
+  ret void
+}

test/Transforms/SROA/slice-width.ll

@@ -0,0 +1,25 @@
+; RUN: opt < %s -sroa -S | FileCheck %s
+target datalayout = "e-p:64:64:64-p1:16:16:16-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:32:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-n8:16:32:64"
+
+declare void @llvm.memcpy.p0i8.p0i8.i32(i8* nocapture, i8* nocapture, i32, i32, i1) nounwind
+
+define void @no_split_on_non_byte_width(i32) {
+; This tests that allocas are not split into slices that are not byte width multiple
+  %arg = alloca i32 , align 8
+  store i32 %0, i32* %arg
+  br label %load_i32
+
+load_i32:
+; CHECK-LABEL: load_i32:
+; CHECK-NOT: bitcast {{.*}} to i1
+; CHECK-NOT: zext i1
+  %r0 = load i32* %arg
+  br label %load_i1
+
+load_i1:
+; CHECK-LABEL: load_i1:
+; CHECK: bitcast {{.*}} to i1
+  %p1 = bitcast i32* %arg to i1*
+  %t1 = load i1* %p1
+  ret void
+}