[SROA] Fix PR24463, a crash I introduced in SROA by allowing it to

handle more allocas with loads past the end of the alloca.

I suspect there are some related crashers with slightly different
patterns, but I'll fix those and add test cases as I find them.

Thanks to David Majnemer for the excellent test case reduction here.
Made this super simple to debug and fix.

llvm-svn: 246289

2 files changed, 36 insertions, 3 deletions

diff --git a/llvm/lib/Transforms/Scalar/SROA.cpp b/llvm/lib/Transforms/Scalar/SROA.cpp
index d37d1e753eb..cd9f8bfaa68 100644
--- a/llvm/lib/Transforms/Scalar/SROA.cpp
+++ b/llvm/lib/Transforms/Scalar/SROA.cpp
@@ -2471,9 +2471,19 @@ private:
     V = convertValue(DL, IRB, V, IntTy);
     assert(NewBeginOffset >= NewAllocaBeginOffset && "Out of bounds offset");
     uint64_t Offset = NewBeginOffset - NewAllocaBeginOffset;
-    if (Offset > 0 || NewEndOffset < NewAllocaEndOffset)
-      V = extractInteger(DL, IRB, V, cast<IntegerType>(LI.getType()), Offset,
-                         "extract");
+    if (Offset > 0 || NewEndOffset < NewAllocaEndOffset) {
+      IntegerType *ExtractTy = Type::getIntNTy(LI.getContext(), SliceSize * 8);
+      V = extractInteger(DL, IRB, V, ExtractTy, Offset, "extract");
+    }
+    // It is possible that the extracted type is not the load type. This
+    // happens if there is a load past the end of the alloca, and as
+    // a consequence the slice is narrower but still a candidate for integer
+    // lowering. To handle this case, we just zero extend the extracted
+    // integer.
+    assert(cast<IntegerType>(LI.getType())->getBitWidth() >= SliceSize * 8 &&
+           "Can only handle an extract for an overly wide load");
+    if (cast<IntegerType>(LI.getType())->getBitWidth() > SliceSize * 8)
+      V = IRB.CreateZExt(V, LI.getType());
     return V;
   }
 
diff --git a/llvm/test/Transforms/SROA/basictest.ll b/llvm/test/Transforms/SROA/basictest.ll
index 009f16a80bb..25b8e8ba41f 100644
--- a/llvm/test/Transforms/SROA/basictest.ll
+++ b/llvm/test/Transforms/SROA/basictest.ll
@@ -1609,3 +1609,26 @@ entry:
   %load = load atomic volatile i64, i64* %ptr seq_cst, align 8
   ret void
 }
+
+define i16 @PR24463() {
+; Ensure we can handle a very interesting case where there is an integer-based
+; rewrite of the uses of the alloca, but where one of the integers in that is
+; a sub-integer that requires extraction *and* extends past the end of the
+; alloca. In this case, we should extract the i8 and then zext it to i16.
+;
+; CHECK-LABEL @PR24463(
+; CHECK-NOT: alloca
+; CHECK: %[[SHIFT:.*]] = lshr i16 0, 8
+; CHECK: %[[TRUNC:.*]] = trunc i16 %[[SHIFT]] to i8
+; CHECK: %[[ZEXT:.*]] = zext i8 %[[TRUNC]] to i16
+; CHECK: ret i16 %[[ZEXT]]
+entry:
+  %alloca = alloca [3 x i8]
+  %gep1 = getelementptr inbounds [3 x i8], [3 x i8]* %alloca, i64 0, i64 1
+  %bc1 = bitcast i8* %gep1 to i16*
+  store i16 0, i16* %bc1
+  %gep2 = getelementptr inbounds [3 x i8], [3 x i8]* %alloca, i64 0, i64 2
+  %bc2 = bitcast i8* %gep2 to i16*
+  %load = load i16, i16* %bc2
+  ret i16 %load
+}